Reusable Code

Force SSL in VB.NET

2011-09-20T10:18:00.000-07:00

Today I'm wrapping up a project to convert an existing web site to use SSL communication only. This required adding HTTPS detection in various places to prevent mixed-content errors. I'm not entirely happy with my solution for that yet, so I'm not going to go into that right now.

What I do want to talk about is actually forcing the user over to HTTPS once your site is SSL-ready. The code I had used for many years on classic ASP sites was not working reliably; it would redirect, but to the home page instead of the page you tried to access.

ASP.NET has beefed up the Request object with some additional information we didn't have back in the old days (Request.IsSecureConnection and Request.Url). We also have a new way of including our function libraries, the App_Code folder.

NameSpace myApplication
Public Class myLibrary
Public Shared Sub ForceSSL()
If Not System.Web.HttpContext.Current.Request.IsSecureConnection Then
System.Web.HttpContext.Current.Response.Redirect(System.Web.HttpContext.Current.Request.Url.AbsoluteUri.Replace("http://", "https://"))
End If
End Sub
End Class
End NameSpace

Then from each page on the site I import my custom library and run the subroutine:

Imports myApplication.myLibrary
Sub Page_Load(sender as Object, e as EventArgs)
ForceSSL()
'Rest of code goes here...
End Sub

Supposedly there's a way to do this without code by modifying some settings in IIS, but I didn't have any success with that. The particular situation I'm dealing with has some fairly severe cohesion/coupling issues with certain pages being accessed from different subdomains.

Download the VB.NET source code for ForceSSL from Snipplr.com

Temperature Conversion Revisited

2011-05-10T17:59:00.001-07:00

I recently completed another ASP.NET project and learned about the app_code folder, which lets you share code between pages. It's slightly similar to the #include directive in Classic ASP, but a lot more structured. I couldn't find much good documentation on it, so most of what I've learned has been through experimentation.

Any files placed into the app_code folder are automatically available from any page in your web application, so you can write: myNamespace.myClass.myFunction(someVariable) and the magic will happen. Alternatively, you can add Imports myNamespace.myClass in the top of your page and call myFunction without all the prefixing.

Though I'm still not a big fan of ASP.NET, this app_code thing is pretty slick and it's inspired me to write more reusable code. I had previously written a collection of functions for temperature conversion, which I've since grown unhappy with after reading Code Complete 2.0 by Steve McConnell because I named my functions like this: CelsiusToFahrenheit, instead of like this: FahrenheitFromCelsius.

I had been planning to write more conversion functions for various units of measurement, but was never satisfied enough with how it was turning out to make it publically available. Besides learning to appreciate ASP.NET, I'm also learning to appreciate object-oriented programming. This whole namespace/class combination with app_code seems to be appropriately suited for doing unit of measurement conversion.

So here's my plan. I've defined a namespace called UOM, which is the manufacturing industry standard abbreviation for unit of measure. Each type of measurement will be a class: temperature, distance, volume, mass, etc. Each class will accept string input so that you can specify both the numeric quantity and the unit of measure simultaneously. The class will use the specified unit of measure to convert values to a common unit of measure, and be able to return values in any equivalent unit of measure.

VB.NET

Imports UOM
Dim outside as Temperature
outside = New Temperature("10 C")
Response.Write(outside.getFahrenheit) 'Displays "50"

And so I proudly announce the release of the first installment in the UOM namespace: UOM.Temperature, which handles Celsius, Delisle, Fahrenheit, Kelvin, Newton, Rankine, Réaumur, and Rømer temperature scales.

Download the VB.NET source code for UOM.Temperature from Snipplr.com

Scalable Site Structure

2010-09-14T17:01:00.000-07:00

If you've been developing web sites for a few years, you've probably developed a lot of sites with a structure similar to the following:

/css/
/images/
/scripts/
index.php
about.php
products.php

One of my colleagues likes to keep the root directory as clean as possible, so his site structures look like this:

/content/about.php
/content/products.php
/common/
/images/
index.php

Which I find slightly irritating because I prefer to keep my CSS separate from my JavaScript, and the /content/ folder is just taking the mess from one place and moving it to another.

Of course, the Holy Grail of site structures is to have clean URLs like this:

/about/
/css/
/images/
/products/
/scripts/
index.php

If you have a dynamic site, this is easily achieved using mod_rewrite, so /about/ becomes index.php?page=about, but sometimes the client doesn't want to pay for a dynamic site. In that case we use the Poor Man's Clean URLs™ wherein we actually create the /about/ and /products/ folders and put an index.php file in each with the static content. The PHP is then only really used to include a header, footer, navigation, etc.

As a site grows, performance and scalability become a (greater) concern. Popular site speed analysis tools often recommend using a content distribution network. Whether you outsource this or try to do it in-house, it sounds like a lot of work.

I hadn't had the privilege of working on a site that experienced enough traffic to be concerned about scalability until earlier this year. The company was running a national television commercial. They had hired another company to develop a micro-site on a separate server for the campaign, but viewers were being directed to the regular corporate site where a gigantic ad enticed them to visit the micro-site. If you're shaking your head right now, me too. The corporate web server was going down almost daily.

The web statistics package indicated that the most downloaded files were the product videos. I still don't know why they aren't using YouTube or Vimeo for this purpose. On a hunch, I copied the video files to the micro-site's web server and changed all the links. They experienced zero downtime after that.

This experience made me think about how to build scalability into a site from the beginning. Something in the back of my mind twigged a memory of reading something about serving static content from a cookieless domain. Cookies aside, it turns out that serving content from multiple subdomains has certain performance advantages.

Any discussion of clean URLs would not be complete without mentioning www.example.com vs. example.com. Dropping the www seems to be the "cool" thing to do, but my personal feeling is that www.example.com is more descriptive of what you will find there. The mail server is mail.example.com, so the web server should be www.example.com.

So here's the site structure I'm planning to use for future projects:

/css/ - css.example.com
/images/ - images.example.com
/images/logos/ - images.example.com/logos/
/images/products/ - images.example.com/products/
/js/ - js.example.com
/www/ - www.example.com
/www/about/ - www.example.com/about/
/www/products/ - www.example.com/products/
/www/index.php - the actual home page
/index.php - file which redirects to www.example.com

The subdomains can be hosted from the primary web server while traffic is small, and migrated to dedicated servers when the traffic increases. The URLs to the images, scripts, and stylesheets don't change, so the PHP files don't need to be updated. Use plenty of folders to keep things organized. You can see I made folders at images.example.com to keep the logos separate from product pictures. If there will be a lot of pictures for each product, I would make folders within the products folder to keep them segregated.

Roman Numerals, Part 4

2010-09-05T13:17:00.000-07:00

Keith Alexander of Albuquerque, New Mexico writes:

“I like your Roman Numeral library. I needed a function to test for Roman numerals, so I wrote this one.
// Check to see if the string is a Roman Numeral
// NOTE: this doesn't check for fractions, overbars, the Bede "N" (zero) etc.
// NOTE: It also doesn't check for a well-formed Roman Numeral.
function is_roman_numeral( $roman )
{
    // Strip every non-word character
    // - A-Z, 0-9, apostrophe and understcore are what's left
    $roman = preg_replace( "/[^A-Z0-9_']/iu", "", $roman );
    // if it contains anything other than MDCLXVI, then it's not a Roman Numeral
    $result = preg_match( "/[^MDCLXVI]/u", $roman );
    if( $result )
    {
        return FALSE;
    }
    return TRUE;
}

Who knows if blogger is going to show it properly. If not, just contact me and I'll send it you in email or something. Anyway, it's something I wrote in 5 minutes. If you want to add it to your library, modified or otherwise, please feel free.”

Thanks for writing in Keith, and sorry for the late response. There are two ways to validate a Roman number, using regular expressions like you did, and converting back to an Arabic number (if the conversion fails, it's not a Roman number).

I'm not sure about using a regular expression to remove non-word characters. My gut tells me that anything containing such characters should fail validation as a Roman number. Also, I would reverse the match and eliminate the if statement by directly returning the result of the match.

PHP

function isRoman($roman)
{
return preg_match("/[MDCLXVI]/u", $roman);
}

ASP

function isRoman(roman)
dim regEx
set regEx = new RegExp
with regEx
.IgnoreCase = true
.Global = true
.Pattern = "[MDCLXVI]"
end with
if regEx.Test(roman) then
isRoman = true
else
isRoman = false
end if
set regEx = nothing
end function

Calculating annual salary for employees paid hourly

2010-09-05T10:29:00.001-07:00

Last time I explained how to calculate the annual salary for an employee who is paid by the hour. Today I'm going to show you by writing a function for it, and we'll write one for monthly salary too.

function annualSalary(someYear, hourlyPay)
const hoursPerDay = 8
annualSalary = 0
for i = 1 to 12
annualSalary = annualSalary + WorkingDays(someYear, i) * hoursPerDay * hourlyPay
next
end function
function monthlySalary(someYear, someMonth, hourlyPay)
const hoursPerDay = 8
monthlySalary = 0
monthlySalary = monthlySalary + WorkingDays(someYear, someMonth) * hoursPerDay * hourlyPay
end function

View ASP implementation on Snipplr

Number of working days in a month

2010-09-01T14:18:00.000-07:00

I didn't realize it's been over a year since my last post. Most of the code I've written this past year has been too specialized to be considered useful to anyone outside of my present employer, but this week I was presented with a problem with our Intranet application where the annual salary of employees who are paid hourly was not being calculated correctly. I'm working with the application vendor to get this corrected in the next version, and learned some interesting things about how to calculate this correctly.

A common formula to calculate annual salary for hourly employees is hourly pay × 40 hours/week × 52 weeks/year. This is very close to accurate, but 365/366 days per year does not divide evenly by 7 days/week.

A more accurate result can be obtained by multiplying the hourly pay by the number of working hours in a year. One way to calculate this is based on the last day of the year. In a non-leap year, there are 2080 working hours if the last day of the year is a Saturday or Sunday, and 2088 working hours if the last day of the year is a weekday. In the case of a leap year, there are 2080 working hours if the last day of the year is a Sunday, 2088 working hours if the last day of the year is a Saturday or Monday, and 2096 working hours for any other weekday.

At our company, we work 8 hours each day, so we can calculate the number of working days rather than the number of working hours and multiply by 8 hours/day. Since the number of days per month is variable, I decided to calculate working days per month separately and sum them up for working days per year.

Function WorkingDays(someYear, someMonth)
WorkingDays = 0
For i = 1 To MonthDays(someYear, someMonth)
If Weekday(DateSerial(someYear, someMonth, i)) <> 1 And Weekday(DateSerial(someYear, someMonth, i)) <> 7 Then
WorkingDays = WorkingDays + 1
End If
Next
End Function

You can take the result and multiply by 8 hours/day to get the number of working hours in a month, and then multiply by the hourly pay to get the monthly salary. The annual working days can be obtained by calling the function in a for i = 1 to 12...next loop, multiplied by 8 hours/day to get the number of working hours in a year, and then multiplied by the hourly pay to get the annual salary.

We ignore holidays and vacation days since the employee is paid for those as well, though technically vacation pay is accured at 4% so you could subtract vacation days (probably either 10 or 15, depending on number of years of service) and multiply by 1.04 to get an even more accurate amount for annual salary.

View ASP implementation on Snipplr.

Publishing schedule change

2009-06-06T08:46:00.000-07:00

As I mentioned last week, I ran out of code samples that are suitable for publishing. All that remains is code in various states of partial completion. I was trying to avoid this, but have decided I need to change the publishing schedule of this blog from weekly to whenever I have something finished. I have some fairly large projects on the go right now that I need to focus on if I hope to complete them in my own lifetime. I'm not even sure that anyone is ever reading this besides myself as I type it, so I don't expect anyone will be upset by this.

Dynamic Arrays

2009-05-30T17:22:00.000-07:00

I have to shamefully admit... I didn't prepare anything for this week. I'd hate to post nothing, so instead I'll post something which I don't consider completely finished yet, but it's far enough along that it probably works just fine.

Working with arrays in classic ASP is frustrating. I wanted to make it more like working with listbox controls in Visual Basic. Note that I wrote this class before I started learning ASP.NET; I wanted to revamp it to bring it in line with the ArrayList class in VB.NET, but just haven't had time yet. More importantly, I haven't really had reason. All my current projects are in PHP or ASP.NET; I've essentially abandoned classic ASP. But I know there are people out there with classic ASP applications which they can't completely rewrite, so I intend to continue writing classic ASP functions.

Considering the enormous size of this class, there's no way I'm going to attempt posting it here, but it'll be on Snipplr as usual. Count, Item, and Items are implemented as properties. Subroutines and functions include: Remove, RemoveAll, Add, BinarySearch, Exists, Random, Reverse, Sort (calls QuickSort; also available are BubbleSort, CombSort, ExchangeSort, and SelectionSort), Shuffle, Swap, Sum, and Product.

View ASP implementation on Snipplr

Prime Numbers

2009-05-23T08:06:00.000-07:00

Once upon a time I wrote some functions for finding and checking prime numbers. In this library of functions you'll find the following:

getPrimes() - finds prime numbers up to a specified limit
isPrime() - checks if a number is prime using modular division against odd numbers
isPrime2() - checks if a number is prime using modular division against known primes
primeCount() - counts the number of primes less than or equal to the specified number
isComposite() - the opposite of prime
isPrimeSpeedTest() - races isPrime againts isPrime2

In theory, checking against known primes should be faster than checking against all odd numbers, but it turned out to be slower because I was first finding the primes with getPrimes(). If a list of prime numbers was hardcoded in an array it might be faster for smaller numbers, and then the odd number method could be used for larger numbers.

View ASP implementation on Snipplr

Chemistry Library

2009-05-16T09:36:00.000-07:00

This week's code is probably the biggest single release I've ever made. I considered splitting it up into two or three weeks, but that would be too much work. Before we get started, you'll need my proper case function.

In this function library, we have three major things going on: look up chemical element symbols by atomic number, look up chemical element names by atomic number, and figure out the electron configuration of an atom given the atomic number.

For the chemical element names and symbols, I made an array of all the named elements; currently the highest named element is atomic number 111. There are elements with higher atomic numbers that have been discovered, but not yet named. There is also the possibility that more elements may be discovered in the future. To handle both these situations, I wrote code to generate standardized names if the array lookup fails.

The function(s) for figuring out electron configuration are my favorite. I started with an array of all the subshells in the order they get filled. Then I wrote a function that knows how many electrons can fit in each type of subshell. Finally, I wrote the main function which fills the subshells, taking into account known exceptions to the rules. (e.g. palladium)

Fuel consumption

2009-05-09T07:47:00.000-07:00

Last November I was at a Service Canada office and picked up a pamphlet called Fuel Consumption Guide 2007. Although too old to be relevant (unless you're buying a used car), it contained some formulae for calculating fuel consumption which inspired me to write some code.

This library of functions is among the longest yet, so I won't be posting the code directly on the blog, but here's a list of the functions included:

lph() - Calculate fuel consumption rating in litres per 100 kilometres.
mpg() - Calculate fuel consumption rating in miles per gallon.
lph2mpg() - Convert miles per (imperial) gallon to litres per 100 kilometres.
mpg2lph() - Convert litres per 100 kilometres to miles per (imperial) gallon.
fuelConsumption() - Calculate fuel consumption in litres.
CO2emissions() - Calculate carbon dioxide emissions in kilograms.

Regular Expressions

2009-05-02T08:13:00.000-07:00

Over the past year, I've posted a lot of code that made use of regular expressions. When used appropriately, they can be very powerful. But regular expressions in ASP are a little more cumbersome than PHP. Wouldn't it be great if ASP had the simplicity of regular expression functions?

Once again, the source code is too long to post here, so it will only be available on Snipplr. This library of functions includes the following:

ereg() - case-sensitive regular expression match
eregi() - case-insensitive regular expression match
ereg_replace() - case-sensitive regular expression replacement
eregi_replace() - case-insensitive regular expression replacement
sql_regcase() - make regular expression for case insensitive match

View ASP implementation on Snipplr

Social Insurance Numbers

2009-04-25T09:14:00.000-07:00

Here in Canada, our equivalent of the Social Security Number is called Social Insurance Number. It serves the same purpose and has the same demands for privacy surrounding it.

Once again, I won't be posting the full source code on the blog, only on Snipplr, but I will discuss briefly how it works. It consists of three groups of three digits, and is validated using the Luhn algorithm. I also do a quick regular expression validation to check for numbers which invalidly begin with an eight: ^([1-79]{3})[\-\s]?(\d{3})[\-\s]?(\d{3})$.

Social Security Numbers

2009-04-18T07:50:00.000-07:00

Assuming that you have a legitimate need to capture social security numbers (human resources app?), you may want to validate and format them consistently. The actual code for both languages combined is a little bit too long to post, so I'll just talk about the algorithm.

A social security number is a nine-digit number and can be matched with the following regular expression: ^\d{3}\-?\d{2}\-?\d{4}$. If it can't pass this test, it's not a valid social security number. However, passing this simple test doesn't guarantee validity, so we need to keep checking.

No digit group can consist of only zeros, and the first group cannot be 666. We check for these errors with the following regular expression: ((000|666)\-?\d{2}\-?\d{4}|\d{3}\-?00\-?\d{4}|\d{3}\-?\d{2}\-?0000.

Numbers from 987-65-4320 to 987-65-4329 are reserved for use in advertisements, and other previously legitimate numbers have been invalidated because of use in advertisments. We check for these errors with the following regular expression: 987\-?65\-?432\d{1}|042\-?10\-?3580|062\-?36\-?0749|078\-?05\-?1120|095\-?07\-?3645|128\-?03\-?6045|135\-?01\-?6629|141\-?18\-?6941|165\-?(16|18|20|22|24)\-?7999|189\-?09\-?2294|212\-?09\-?(7694|9999|219\-?09\-?9999|306\-?30\-?2348|308\-?12\-?5070|468\-?28\-?8779|549\-?24\-?1889)

Last but not least, the first three numbers are never higher than 772 (well, not yet; this could change in the future). For this I used a simple string conversion and numeric comparison.

The complete, commented source code is available on Snipplr:

Next week we'll head north of the border to my country and see what the Canadian equivalent of the Social Security Number is, and how we can validate them.

Homeland Security Advisory System

2009-04-11T07:20:00.000-07:00

Back in 2002, a bunch of bureaucrats decided that the United States needed an advisory system so that all federal departments and agencies could communicate what the current threat condition was using the same definitions. Sounds like a good idea to me.

The average citizen can see what the current threat condition is by visiting certain government web sites. The web site for the Department of Homeland Security is a good example.

The Department of Homeland Security also provides a little-known web service which returns the threat condition in XML format so that you can do what you want with it. Let's write a function to retrieve and parse this information down to just the threat condition itself.

ASP

function getThreatLevel()

dim regEx

set regEx = new RegExp

with regEx

.Pattern = ".*\n.*CONDITION=""(.*)"" />"

.IgnoreCase = true

.Global = true

end with

dim xmlhttp

set xmlhttp = Server.CreateObject("Msxml2.ServerXMLHTTP")

xmlhttp.open "GET", "http://www.dhs.gov/dhspublic/getAdvisoryCondition", "False"

xmlhttp.send

getThreatLevel = regEx.replace(xmlhttp.responseText, "$1")

set xmlhttp = nothing

set regEx = nothing

end function

As is often the case, the PHP version requires a significantly less amount of code.

PHP

function getThreatLevel()

return eregi_replace('.*CONDITION="(.*)" />', '\1', file_get_contents("http://www.dhs.gov/dhspublic/getAdvisoryCondition"));

So now we have a string that contains just the word "ELEVATED" (or whatever the current threat level is at the moment; it's been at elevated for several years at the time of this writing). What can you do with it? Feed it into a switch statement and display an image is one possibility.

Min/Max

2009-04-04T08:08:00.001-07:00

SQL contains a number of aggregate functions that can do things like select the largest or smallest number from a set of values. This could be handy in the programming language itself.

ASP

function max(arrNumbers)
dim result
result = arrNumbers(0)
for each i in arrNumbers
if i > result then
result = i
end if
next
max = result
end function
function min(arrNumbers)
dim result
result = arrNumbers(0)
for each i in arrNumbers
if i < result then
result = i
end if
next
min = result
end function

View ASP implementation on Snipplr

getFileType

2009-03-28T08:34:00.000-07:00

Last week I showed you how to get the size of a file. This week I'm going to show you how to get the type of a file. This is useful if you want to display an icon or bit of text next to a hyperlink to indicate the file type. Some people like to use this to warn visitors when they link to a PDF file, because PDF readers can take a while to load.

ASP

function getFileType(someFile)
dim fs
set fs = Server.CreateObject("Scripting.FileSystemObject")
getFileType = fs.GetExtensionName(Server.MapPath(someFile))
set fs = nothing
end function

See you next week!

View ASP implementation on Snipplr

getFileSize

2009-03-21T08:58:00.000-07:00

When you provide a link to a file for the user to download, it's sometimes nice to provide the size of the file so that they know what they're getting themselves into.

ASP

function getFileSize(someFile)
dim fs
dim file
set fs = Server.CreateObject("Scripting.FileSystemObject")
set file = fs.GetFile(Server.MapPath(someFile))
getFileSize = FormatFileSize(file.size)
set file = nothing
set fs = nothing
end function

The size property returns the size in bytes, which could be a very large number. As you may have guessed, we're going to write a FormatFileSize function to wrap around it.

ASP

function FormatFileSize(size)
dim units
dim factor
units = Array("B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB")
factor = log(size) \ 7
FormatFileSize = Round(size / (1024 ^ factor), 2) & units(factor)
end function

I think it will be a very, very long time before we reach yottabytes, so this function should withstand the test of time. Next week I'll show you how to get the file type and why you might want that.

View ASP implementation on Snipplr

Soundex

2009-03-14T07:36:00.000-07:00

This week we're going to write a function to convert letters to their corresponding soundex codes. But wait, there's more! We'll also allow you to pass in an entire string and convert the whole thing. Here's the set up:

function soundex(someString)
if len(someString) = 1 then
' code to convert a single character
else
' loop through the whole string and convert each character
end if
end function

Inside the loop, we'll recursively call the soundex function to convert the individual character. Actually, this may not perfectly fit the definition of recursion. The only recursive aspect of it is that the function calls itself, but an entirely different execution path is being followed once inside. But that's good, because we won't have the poor performance that sometimes comes with recursion.

Once again, the full source code is a little too long to post, so you'll have to grab it from Snipplr:

Luhn Algorithm

2009-03-07T07:33:00.000-08:00

This week we're writing a function to verify credit card numbers. Credit cards have a check digit which is generated with the Luhn algorithm. The code is too long to post here, but as always it is posted on Snipplr and linked here for your dissemination.

Phonetic Alphabet

2009-02-28T06:09:00.000-08:00

It seems to me that most people have trouble remembering the phonetic alphabet (probably myself included). Unless you're a pilot or air traffic controller, it's unlikely that your job requires you to have it memorized. People get by with whatever word comes to mind ("A as in Adam"), but this seems like an opportunity to write some code.

For maximum reusability, I'm going to write my function to convert individual characters at a time. Looping through the characters of the string will occur outside the function. The function is too long to paste here in its entirety, but it will be posted on Snipplr and linked at the bottom of this entry.

PHP has key/value arrays where we can specify any keys we want, so we'll declare an array containing all the conversions and use the input to retrieve the correct string from the array. ASP's arrays don't have this flexibility; we could achieve this with a Dictionary scripting object, but I'm concerned about the overhead associated with that. I'm going to use a Select...Case statement (AKA switch statement), but there is a chance that this is actually not any better. I'll leave the determination of this as an exercise to the reader. Also left as an exercise to the reader is the writing of the looping code.

Add and strip slashes

2009-02-21T15:48:00.000-08:00

Good programmers know that they can't trust user-inputted data. We do as much as we can to validate and try to prevent bad data from getting into our applications. But there is even some perfectly valid data that can cause trouble, especially when you're dealing with databases. The single apostrophe is a common occurrence and gotcha for the newbies when they discover the tail end of their string didn't make it into the database.

Our PHP programmer friends have a few different functions at their disposal. Native to PHP are the addslashes() and stripslashes() functions, which basically do what they say. In more common usage these days is the MySQL-native function, mysql_real_escape_string(), which can handle a wider variety of situations. I'm going to go a little bit further and handle the backspace and horizontal tab characters.

The regular expression we'll be using to add slashes is ([\000\010\011\012\015\032\042\047\134\140]), and to remove slashes we'll use \\([\000\010\011\012\015\032\042\047\134\140]). The only difference is the extra pair of slashes at the beginning. These handle, respectively: null, backspace, horizontal tab, new line, carriage return, substitute, double quote, single quote, backslash, and grave accent.

htmlspecialchars()

2009-02-14T07:58:00.000-08:00

If you rigoursly validate your HTML like I do, you've probably seen many times the warning about HTML entities. Inevitably an ampersand makes its way into your code without being properly encoded. It's almost always in a hyperlink where you're trying to pass a QueryString variable or two.

somefile.asp?this=that&blah=meh

That ampersand needs to be encoded as &. Likewise, double quotation marks need to be encoded as " and the greater than and less than symbols need to be encoded as > and < respectively. If you allow users to write things on your web site, then you need a programmatic solution. Our PHP programmer friends have one in their toolbox which we can borrow.

function htmlspecialchars(someString)
' Critical that ampersand is converted first, since all entities contain them.
htmlspecialchars = replace(replace(replace(replace(someString, "&", "&"), ">", ">"), "<", "<"), """", """)
end function
function htmlspecialchars_decode(someString)
htmlspecialchars_decode = replace(replace(replace(replace(someString, "&", "&"), ">", ">"), "<", "<"), """, """")
end function

View ASP implementation on Snipplr

Difference between two stardates

2009-02-07T08:29:00.000-08:00

As promised last week, I rejigged my code to calculate the difference between two stardates into a proper function and translated it to ASP. I don't have access to an IIS server right now, so I didn't have a chance to test the ASP version yet, but I'm fairly confident that it works. Let me know if it doesn't!

I won't post the source code directly into this post like I usually do, but as usual it will be available on Snipplr. Expect to see this happen more often in the future. However, I'll talk briefly about what's going on under the hood.

The incoming stardates are just strings, and we split them up based on the official format: first two characters to calculate the years, next three characters to calculate the days, and last character to calculate the hours. The order of the stardates is not important - the code checks which is larger. The same magic numbers from last week are used to get the real values, which are then subtracted. After rounding off any decimal places, the three values are formatted into a human-readable string and returned. It should be very straight-forward.

Stardate

2009-01-31T21:10:00.000-08:00

As promised, today was to be a celebration of one year of Reusable Code. That celebration was overshadowed by a catastrophic hard drive failure early this morning, but luckily I managed to perform a successful recovery with Windows Home Server (after much trial and error).

The function I'm going to share this week is my favorite: calculating the stardate for a given Gregorian calendar date. If you're not familiar with the various Star Trek television series, you might not know what a stardate is. It's a fictional method of measuring time, which is supposed to solve the problems of relativistic time dilation caused by travelling at high velocity. In reality, it progressed at the same rate as time here on Earth.

The method of stardate calculation used here is based on Star Trek: the Next Generation, Star Trek: Deep Space Nine, and Star Trek: Voyager. It does not take the Original Series into account. Also, it is calibrated with the airdates of the television series, not with real world dates. That is to say, if you pass in today's date, it does not return the stardate corresponding to today's date in the 21st century, but today's date in the 24th century Star Trek universe. This is intended to be beneficial for roleplaying games.

ASP

function stardate(someDateTime)
dim season
dim episode
dim fractime
season = cStr(Year(someDateTime) - 1947)
episode = str_pad(Round(1000 / 366 * DatePart("y", someDateTime), 0), 3, "0", "left")
fractime = left(cStr((Hour(someDateTime) * 60 + Minute(someDateTime)) / 144), 1)
stardate = season & episode & "." & fractime
end function

It is important to note here that for the above function, you will also need my str_pad() function.

PHP

function stardate($timestamp)
{
$season = date("Y", $timestamp) - 1947;
$episode = str_pad(round(1000 / 366 * (date("z", $timestamp) + 1)), 3, "0", STR_PAD_LEFT);
$fractime = substr((date("g", $timestamp) * 60 + date("i", $timestamp)) / 144, 0, 1);
return $season . $episode . "." . $fractime;
}

I'm somewhat ashamed to admit that there are some "magic" numbers at play here. When I originally wrote this function, I had not intended to make it open source, but events over the past year have led me to the realization that if I did not, it would become lost in the sands of time.

Once upon a time I also wrote some code to calculate the difference between two stardates, but it was only written in PHP. I'll have to port it to ASP and perhaps have it ready for next Saturday's posting, but no promises.

A year of reusable code

2009-01-24T10:59:00.000-08:00

In just a few more days, it will be one year since I started this blog. Next week Saturday I plan to mark the occasion by sharing with you, one of my most favorite functions. In the weeks following that, I'll be bringing you some larger functions and function libraries which will hopefully make up for some of the less interesting things I've posted over the past year. Unfortunately I can't promise no more boring code, because eventually the good stuff will run out.

If I'm going to be completely honest, some of the functions I've posted here, I wrote specifically for here. The tag line of this blog purports "Practical examples for real-world progrmaming", and I feel that sometimes I wasn't really living up to that. However, I feel to a certain extent that I lived up to what I resolved not to do, which was post silly examples about animals and cars just to illustrate how code works.

Since this is Saturday, I owe you folks some source code. Since next week's code is going to super awesome, I'm going to shamefully post two quick snippets which might seem lackluster, but these were honestly written out of desire/need. Both are re-creations of PHP functions, requested by a PHP programmer that worked for me and had to code in ASP because that's what the existing code was written in.

First we have the echo() function. Our PHP programmer friends are spoiled with not having to type Response.Write every time they want to put something on the screen. Then again, are we not entitled to the same luxuries? Rather than merely aliasing Response.Write, you can also use \n instead of typing vbCrLf.

sub echo(someText)
Response.Write Replace(someText, "\n", vbCrLf)
end sub

Our second function for today was written for use with HTML's textarea element and SQL data types that contain text with line breaks.

function nl2br(someText)
nl2br = Replace(someText, vbCrLf, " ")
end function

Triangular Numbers

2009-01-17T07:56:00.000-08:00

A triangular number is the sum of the n natural numbers from 1 to n.

ASP

function triangularNumber(someNumber)
dim i
dim result
result = 0
for i = 1 to someNumber
result = result + i
next
triangularNumber = result
end function

PHP

function triangularNumber($number)
{
for($i = 1; $i <= $number; $i++)
{
$result += $i;
}
return $result;
}

Array Merge

2009-01-10T07:48:00.000-08:00

Did you ever have two arrays that you needed to merge together? If you were programming in PHP, you used the array_merge() function. If you were programming in ASP, you had to write a whole bunch of code because there is no array_merge() function... until now.

ASP

function array_merge(byVal firstArray, byVal secondArray)
dim totalSize
dim i
dim combinedArray
' Ensure that we're dealing with arrays.
if not isArray(firstArray) then
firstArray = Array(firstArray)
end if
if not isArray(secondArray) then
secondArray = Array(secondArray)
end if
' Set up the new array.
totalSize = uBound(firstArray) + uBound(secondArray) + 1
combinedArray = firstArray
redim preserve combinedArray(totalSize)
for i = 0 to uBound(secondArray)
combinedArray(uBound(firstArray) + 1 + i) = secondArray(i)
next
array_merge = combinedArray
end function

View ASP implementation on Snipplr

Perfect Numbers

2009-01-03T08:05:00.000-08:00

This week's function is for checking if an integer is a perfect number.

ASP

function isPerfect(someNumber)
dim i
dim arrFactors
arrFactors = Array()
' Only positive integers can be perfect.
if someNumber < 1 then
isPerfect = false
exit function
end if
' Calculate the factors for the given number.
for i = 1 to someNumber
if someNumber mod i = 0 then
redim preserve arrFactors(UBound(arrFactors) + 1)
arrFactors(UBound(arrFactors)) = i
end if
next
' A perfect number is a number that is half the sum of all of its positive divisors (including itself).
if someNumber = eval(join(arrFactors, " + ")) / 2 then
isPerfect = true
else
isPerfect = false
end if
end function

PHP

function isPerfect($number)
{
// Only positive integers can be perfect.
if ($number < 1)
{
return false;
}
// Calculate the factors for the given number.
for($i = 1; $i <= $number; $i++)
{
if ($number % $i == 0)
{
$arrFactors[] = $i;
}
}
// A perfect number is a number that is half the sum of all of its positive divisors (including itself).
return ($number == array_sum($arrFactors) / 2) ? true : false;
}

Random Integer

2008-12-27T20:54:00.000-08:00

Our PHP programmer friends have a function called randInt() which returns a random integer between two specified integers. It's time to level the playing field.

ASP

function randInt(min, max)
Randomize
randInt = Int((max - min + 1) * Rnd + min)
end function

View ASP implementation on Snipplr

strip_tags()

2008-12-20T20:17:00.000-08:00

This week we're recreating a PHP function that is extremely important for sanitizing user input. All HTML/ASP/PHP tags are stripped outright; there is no support for a whitelist of allowed tags. A whitelist can be very dangerous without much more rigorous testing to check for script-related exploits. A safer solution would be to force the user to use something like UBB code or Markdown and convert to HTML on the backend.

ASP

function strip_tags(unsafeString)
dim regEx
set regEx = new RegExp
with regEx
.Global = true
.IgnoreCase = true
.Pattern = "(\<(/?[^\>]+)\>)"
end with
strip_tags = regEx.Replace(unsafeString, "")
set regEx = nothing
end function

View ASP implementation on Snipplr

isPostBack()

2008-12-13T08:50:00.000-08:00

Today's function comes not from PHP, but ASP.NET. We're going to replicate the isPostBack() function from ASP.NET's Page object.

ASP

function isPostBack()
if uCase(Request.ServerVariables("REQUEST_METHOD")) = "POST" then
isPostBack = true
else
isPostBack = false
end if
end function

PHP

function isPostBack()
{
return ($_SERVER['REQUEST_METHOD'] == 'POST');
}

Summation

2008-12-06T08:37:00.000-08:00

This week's function is summation using the Gauss method.

ASP

function sum(x, y)
sum = (x + y) * ((y - x + 1) / 2)
end function

PHP

function sum($x, $y)
{
return ($x + $y) * (($y - $x + 1) / 2);
}

Swatch Internet Time

2008-11-29T08:19:00.000-08:00

Back in 1998, a company called Swatch decided to invent a new method of timekeeping. It didn't catch on, but some people embraced it. If you're one of those people, this is for you. We're going to write a function to convert a time value into a Swatch beat. Our PHP programmer friends already have access to this sort of thing through PHP's date() function.

The following code builds upon two other functions previously published here:

IMPORTANT: To return an accurate result, the time value passed in needs to be UTC/GMT (in other words, without offset). There are two ways to achieve this: set your server's time zone to GMT, or use my UTC time function.

ASP

function swatch(someTime)
swatch = str_pad(floor(((Hour(someTime) * 3600 * 1000) + (Minute(someTime) * 60 * 1000) + (Second(someTime) * 1000)) / 86400), 3, "0", STR_PAD_LEFT)
end function

View ASP implementation on Snipplr

Mersenne Numbers

2008-11-22T09:44:00.000-08:00

Today we're going to write a function to generate Mersenne numbers. This is useful in searching for Mersenne primes.

ASP

function mersenne(x)
mersenne = 2^x - 1
end function

PHP

function mersenne($x)
{
return 2^$x - 1;
}

UTC and Atomic Time

2008-11-15T08:13:00.000-08:00

In this special double issue, I'm going to show you how to obtain time values in the GMT timezone, as well as ultra-precise atomic clock time values.

Our PHP programmer friends have a slight advantage against us. Their language is aware of what time zone the server is located in and is capable of doing various things with that information, including returning time values without any timezone offset. ASP has no clue what time zone the server is set for, but we can use XMLHTTP to retrieve a time value from a NIST time server.

ASP

function utcnow()
dim xmlhttp
dim response
' Server to query datetime from
Const TimeServer = "http://time.nist.gov:13"
' Use XML HTTP object to request web page content
Set xmlhttp = Server.CreateObject("Microsoft.XMLHTTP")
xmlhttp.Open "GET", TimeServer, false, "", ""
xmlhttp.Send
response = xmlhttp.ResponseText
set xmlhttp = nothing
' Parse UTC date
utcnow = cDate(mid(response, 11, 2) & "/" & mid(response, 14, 2) & "/" & mid(response, 8, 2) & " " & mid(response, 16, 9))
end function

If you were to compare the value returned by this function and the value returned by the built-in Now() function, you might notice more than just the hour value is different. This could mean you live in one of those funky half-hour-offset timezones, or it could mean that your server's clock is off by a few minutes. If accurate time values are important to you, you need a better Now() function. We can build one on top of the UTCnow() function we just wrote.

ASP

function atomicnow()
dim utc
dim offset
utc = utcnow()
' The order of the dates is important here!
offset = DateDiff("h", utc, now())
atomicnow = DateAdd("h", offset, utc)
end function

There is expected to be some lag caused by this function, but the order of magnitude should only be milliseconds.

View implementation on Snipplr

Sinc function

2008-11-08T07:53:00.000-08:00

Today we're going to a Sinc function, both normalized and unnormalized. Apparently it's useful in digital signal processing.

ASP

Const M_PI = 3.14159265358979323846
' Unnormalized sinc function.
function sinc(x)
sinc = sin(x) / x
end function
' Normalized sinc function.
' REQUIRES: constant M_PI
function nsinc(x)
sinc = sin(M_PI * x) / (M_PI * x)
end function

PHP

// Unnormalized sinc function.
function sinc($x)
{
return sin($x) / $x;
}
// Normalized sinc function.
function nsinc($x)
{
return sin(M_PI * $x) / (M_PI * $x);
}

Nth Day

2008-11-01T07:55:00.000-07:00

This week I want to share with you a function that I personally got a lot of use out of. Several years ago I had a situation where there was a calendar with several hundreds recurring events. It was desired to have these events fall on roughly the same day each year. The person responsible for this was spending two or three days at the end of each year planning all the occurrences for the next year on a giant wet-eraseable calendar.

Here's what all the fuss was about: Last year, November 1 was a Thursday. This year, November 1 is a Saturday. Saturday is not a working day for most people, so these events we are scheduling need to fall on week days. Because it fell on a Thursday last year, we'd prefer to have it on a Thursday again this year. This means either pushing it back to October 30 or forward to November 6.

To make the event occur on the same day of the week, we'll store this information in our database and use it to generate the date for a given year. This is called the Nth Day. In the above example, our Nth Day is the first Thursday in November.

ASP

function nthDay(someYear, someMonth, someWeek, someWeekday)
dim firstDay
dim someDay
firstDay = weekday(dateSerial(someYear, someMonth, 1))
' Check if the week day of the first day of the month is before or after the given week day.
if (someWeekday - firstDay) >= 0 then
someDay = 1 + (someWeekday - firstDay) + ((someWeek - 1) * 7)
else
someDay = 1 + (someWeekday - firstDay) + (someWeek * 7)
end if
nthDay = dateSerial(someYear, someMonth, someDay)
end function

If developing a system around this concept like I did, it's important to know that some months have a fifth week, depending on how late in the week the first day of the month is. You can't really schedule anything recurring during the fifth week. We kept it open both to give the people conducting the events a little time off, as well as for a place to move an event from the following month in situations where the customer thought it would be too late in the year otherwise.

An idea I had to improve the system, but didn't get around to exploring, was to ignore the months entirely and use the weeks of the year. Nobody wants to schedule anything around Christmas and New Year's anyway, so you don't run into problems around the beginning/end of the year like you do at the beginning/end of a month. Under this system, first Thursday of November becomes Thursday of Week 44. Scheduling a recurring event this way is not only easier, but also more consistent from year to year.

View ASP implementation on Snipplr

Golden function

2008-10-25T07:28:00.000-07:00

The golden function is the upper branch of the hyperbola.

ASP

function gold(x)
gold = (x + sqr(x^2 + 4)) / 2
end function

PHP

function gold($x)
{
return ($x + sqrt($x^2 + 4)) / 2;
}

Sorry if this is not exciting stuff. I've got some better stuff coming, but I want to clear out some older stuff that has been waiting a while.

Levenshtein distance

2008-10-18T08:36:00.000-07:00

The Levenshtein distance between two strings is a measurement of similarity. The smaller the distance, the more similar two strings are. Our PHP programmer friends have a function to calculate this distance; we deserve one too.

ASP

function levenshtein(byVal first, byVal second)
dim distance
dim truncateLength
if first = second then
' The distance is zero if the strings are identical.
distance = 0

else
' The distance is at least the difference of the lengths of the two strings.
distance = abs(len(first) - len(second))
' Force the strings to be the same length to prevent overflows.
truncateLength = ((len(first) + len(second)) - distance) / 2
first = Left(first, truncateLength)
second = Left(second, truncateLength)
' Compare the corresponding characters in each string.
for i = 1 to truncateLength
if Mid(first, i, 1) <> Mid(second, i, 1) then
distance = distance + 1
end if
next
end if
levenshtein = distance
end function

View ASP implementation on Snipplr

WordCount

2008-10-11T07:53:00.000-07:00

PHP has a function called str_word_count() which allows you to count the number of words in a string, and an array or associative array of those words. Unfortunately for us, ASP doesn't support optional parameters, so we can't duplicate all of this functionality in a single function, so we'll just concentrate on the main feature of counting the number of words.

ASP

function WordCount(byVal someString)
dim position
dim spaces
spaces = 1
someString = trim(someString)
for position = 1 to len(someString)
if mid(someString, position, 1) = " " and not mid(someString, position - 1, 1) = " " then
spaces = spaces + 1
end if
next
WordCount = spaces
end function

View ASP implementation on Snipplr

Nth Root

2008-10-04T07:46:00.000-07:00

Both ASP and PHP have a function that allows you to calculate the square root of a number. What if we wanted the cubic root of a number, or some deeper root? Calculating the root of a number is the same as raising that number to a fractional exponent.

ASP

function root(x, y)
root = x ^ (1 / y)
end function

PHP

function root($x, $y)
{
return pow($x, 1/$y);
}

x: the number you want the root of
y: the depth you want to go (2 = square, 3 = cubic, etc.)

Format a number in scientific notation

2008-09-27T07:22:00.001-07:00

Surprisingly, neither ASP nor PHP seem to have a built-in way of formatting a number in scientific notation. Today we're going to change that.

ASP

function formatScientific(someFloat)
dim power
power = (someFloat mod 10) - 1
formatScientific = cStr(cDbl(someFloat) / 10^power) & "e" & cStr(power)
end function

PHP

function formatScientific($someFloat)
{
$power = ($someFloat % 10) - 1;
return ($someFloat / pow(10, $power)) . "e" . $power;
}

Logarithms

2008-09-21T07:43:00.000-07:00

ASP's log() function returns the natural logarithm of a number. But what if we want a different base? The same problem exists with handheld calculators, and the same trick we use to get around it there can be used here too.

ASP

function logx(number, base)
logx = log(number) / log(base)
end function

View ASP implementation on Snipplr

str_repeat

2008-09-13T07:54:00.000-07:00

This week we're duplicating another string function from PHP: str_repeat().

ASP

function str_repeat(input, multiplier)
dim output
output = ""
for i = 1 to multiplier
output = output & input
next
str_repeat = output
end function

View ASP implementation on Snipplr

str_pad

2008-09-06T06:49:00.000-07:00

PHP has a very useful function called str_pad(). It allows you to ensure that a string will conform to a specific length by adding characters of your choice on the end of your choice. A good practical example is when you want a number with leading zeros. ASP doesn't have an equivalent function out of the box, but we're going to write one today; as usual, we'll follow the same syntax to make it easy for those who are already familiar with PHP.

ASP

Const STR_PAD_LEFT = "LEFT"
Const STR_PAD_RIGHT = "RIGHT"
Const STR_PAD_BOTH = "BOTH"
' Pad a string to a certain length with another string.
function str_pad(input, pad_length, pad_string, pad_type)
dim output
dim difference
output = ""
difference = pad_length - len(input)
if difference > 0 then
select case ucase(pad_type)
case "LEFT"
for i = 1 to difference step len(pad_string)
output = output & pad_string
next
output = right(output & input, pad_length)
case "BOTH"
output = input
for i = 1 to difference step len(pad_string) * 2
output = pad_string & output & pad_string
next
' Not sure if it will step far enough when difference is an odd number, so this next block is just in case.
if len(output) < pad_length then
output = output & pad_string
end if
output = left(output, pad_length)
case else
for i = 1 to difference step len(pad_string)
output = output & pad_string
next
output = left(input & output, pad_length)
end select
else
output = input
end if
str_pad = output
end function

Thinking back to my days as a web developer, this was probably the most reused function out of all I'd ever written.

View ASP implementation on Snipplr

Roman Numerals, Part 3

2008-08-30T08:01:00.000-07:00

Back in March, we wrote a function to turn an arabic number into a Roman numeral. That function had a limitation of numbers smaller than 5000. There are ways of writing Roman numerals larger than 5000, but they are not as well accepted by purists because they evolved during later time periods. Out of respect for the purists, this new function will hinge on the old one, rather than replace it.

In the system we will be using, a bar is placed over the numeral to indicate that it is multipled by 1000:

V = 5000
X = 10,000
L = 50,000
C = 100,000
D = 500,000
M = 1 million

Since there are no Unicode characters for this purpose, we will have to cheat a little bit by using some HTML and CSS.

ASP

function bigroman(ByVal arabic)
dim thousands
thousands = Array("", "M", "MM", "MMM", "M(V)", "(V)", "(V)M", "(V)MM", "(V)MMM", "M(X)")
if arabic >= 10000 then
bigroman = "(" & roman((arabic - (arabic mod 10000)) / 1000) & ")"
arabic = arabic mod 10000
end if
bigroman = bigroman & thousands((arabic - (arabic mod 1000)) / 1000)
arabic = arabic mod 1000
bigroman = bigroman & roman(arabic)
' Convert parentheses to tags.
bigroman = replace(bigroman, "(", "")
bigroman = replace(bigroman, ")", "")
end function

PHP

function bigroman($arabic)
{
$thousands = Array("", "M", "MM", "MMM", "M(V)", "(V)", "(V)M", "(V)MM", "(V)MMM", "M(X)");
if ($arabic >= 10000)
{
$bigroman = "(" . roman(($arabic - fmod($arabic, 10000)) / 1000) . ")";
$arabic = fmod($arabic, 10000);
}
$bigroman .= $thousands[($arabic - fmod($arabic, 1000)) / 1000];
$arabic = fmod($arabic, 1000);
$bigroman .= roman($arabic);
// Convert parentheses to tags.
$bigroman = str_replace("(", "", $bigroman);
$bigroman = str_replace(")", "", $bigroman);
return $bigroman;
}

isValidPostCode

2008-08-23T07:04:00.000-07:00

In this final installment of the postal code trilogy, we turn our attention to the United Kingdom. Postal codes in the UK are called postcodes. They are similar to postal codes in Canada in that they contain both letters and numbers, but unlike Canadian postal codes, they are variable in length.

A postcode can have any of the following formats:

A9 9AA
A99 9AA
A9A 9AA
AA9 9AA
AA99 9AA
AA9A 9AA

To match all of these formats, we'll use the following regular expression: [A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\ [0-9][ABD-HJLNP-UW-Z]{2}. You may notice that, like Canadian postal codes, certain letters are only allowed in certain positions, or not at all.

There are also a few special cases that are valid postcodes but deviate from the regular format:

Girobank - (GIR\ 0AA)
Father Christmas - (SAN\ TA1)
British Forces Post Office - (BFPO\ (C\/O\ )?[0-9]{1,4})
Overseas territories - ((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ)

ASP

function isValidPostCode(postCode)
dim regEx
set regEx = new RegExp
with regEx
.IgnoreCase = true
.Global = true
.Pattern = "^([A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\ [0-9][ABD-HJLNP-UW-Z]{2}|(GIR\ 0AA)|(SAN\ TA1)|(BFPO\ (C\/O\ )?[0-9]{1,4})|((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ))$"
end with
if regEx.Test(trim(CStr(postCode))) then
isValidPostCode = true
else
isValidPostCode = false
end if
set regEx = nothing
end function

PHP

function isValidPostCode($postCode)
{
$pattern = "/^([A-PR-UWYZ]([0-9]{1,2}|([A-HK-Y][0-9]|[A-HK-Y][0-9]([0-9]|[ABEHMNPRV-Y]))|[0-9][A-HJKS-UW])\ [0-9][ABD-HJLNP-UW-Z]{2}|(GIR\ 0AA)|(SAN\ TA1)|(BFPO\ (C\/O\ )?[0-9]{1,4})|((ASCN|BBND|[BFS]IQQ|PCRN|STHL|TDCU|TKCA)\ 1ZZ))$/i";
return (preg_match($pattern, trim($postCode)) > 0) ? true : false;
}

isValidPostalCode

2008-08-16T15:47:00.000-07:00

This week we're turning our attention to my own country, Canada, and writing a function to validate postal codes. Unlike a ZIP code, a postal code contains letters too; the format is A1A 1A1. The simplest regular expression to validate this would be:

^[A-Z]{1}[\d]{1}[A-Z]{1}[ ]?[\d]{1}[A-Z]{1}[\d]{1}$

But not all letters are used, and some letters can only appear in certain positions. Taking this into account gives us a slightly more complex pattern of:

^[ABCEGHJ-NPRSTVXY]{1}[0-9]{1}[ABCEGHJ-NPRSTV-Z]{1}[ ]?[0-9]{1}[ABCEGHJ-NPRSTV-Z]{1}[0-9]{1}$

But I want to take this a step further and check the validity of the combination of the first three characters. The postal code C2B 4S3 has a valid format, but the code itself is not valid because there is no C2B postal area. I also want to check the postal code against the province to ensure that they match.

The full source code is too long to post here, but is available in its entirety from Snipplr in the language of your choice:

Alternatively, if you wanted the extended validation, but didn't care about the province matching, you could combine everything into one gigantic regular expression:

^(A(0[ABCEGHJ-NPR]|1[ABCEGHK-NSV-Y]|2[ABHNV]|5[A]|8[A])|B(0[CEHJ-NPRSTVW]|1[ABCEGHJ-NPRSTV-Y]|2[ABCEGHJNRSTV-Z]|3[ABEGHJ-NPRSTVZ]|4[ABCEGHNPRV]|5[A]|6[L]|9[A])|C(0[AB]|1[ABCEN])|E(1[ABCEGHJNVWX]|2[AEGHJ-NPRSV]|3[ABCELNVYZ]|4[ABCEGHJ-NPRSTV-Z]|5[ABCEGHJ-NPRSTV]|6[ABCEGHJKL]|7[ABCEGHJ-NP]|8[ABCEGJ-NPRST]|9[ABCEGH])|G(0[ACEGHJ-NPRSTV-Z]|1[ABCEGHJ-NPRSTV-Y]|2[ABCEGJ-N]|3[ABCEGHJ-NZ]|4[ARSTVWXZ]|5[ABCHJLMNRTVXYZ]|6[ABCEGHJKLPRSTVWXZ]|7[ABGHJKNPSTXYZ]|8[ABCEGHJ-NPTVWYZ]|9[ABCHNPRTX])|H(0[HM]|1[ABCEGHJ-NPRSTV-Z]|2[ABCEGHJ-NPRSTV-Z]|3[ABCEGHJ-NPRSTV-Z]|4[ABCEGHJ-NPRSTV-Z]|5[AB]|7[ABCEGHJ-NPRSTV-Y]|8[NPRSTYZ]|9[ABCEGHJKPRSWX])|J(0[ABCEGHJ-NPRSTV-Z]|1[ACEGHJ-NRSTXZ]|2[ABCEGHJ-NRSTWXY]|3[ABEGHLMNPRTVXYZ]|4[BGHJ-NPRSTV-Z]|5[ABCJ-MRTV-Z]|6[AEJKNRSTVWYXZ]|7[ABCEGHJ-NPRTV-Z]|8[ABCEGHLMNPRTVXYZ]|9[ABEHJLNTVXYZ])|K(0[ABCEGHJ-M]|1[ABCEGHJ-NPRSTV-Z]|2[ABCEGHJ-MPRSTVW]|4[ABCKMPR]|6[AHJKTV]|7[ACGHK-NPRSV]|8[ABHNPRV]|9[AHJKLV])|L(0[[ABCEGHJ-NPRS]]|1[ABCEGHJ-NPRSTV-Z]|2[AEGHJMNPRSTVW]|3[BCKMPRSTVXYZ]|4[ABCEGHJ-NPRSTV-Z]|5[ABCEGHJ-NPRSTVW]|6[ABCEGHJ-MPRSTV-Z]|7[ABCEGJ-NPRST]|8[EGHJ-NPRSTVW]|9[ABCGHK-NPRSTVWYZ])|M(1[BCEGHJ-NPRSTVWX]|2[HJ-NPR]|3[ABCHJ-N]|4[ABCEGHJ-NPRSTV-Y]|5[ABCEGHJ-NPRSTVWX]|6[ABCEGHJ-NPRS]|7[AY]|8[V-Z]|9[ABCLMNPRVW])|N(0[ABCEGHJ-NPR]|1[ACEGHKLMPRST]|2[ABCEGHJ-NPRTVZ]|3[ABCEHLPRSTVWY]|4[BGKLNSTVWXZ]|5[ACHLPRV-Z]|6[ABCEGHJ-NP]|7[AGLMSTVWX]|8[AHMNPRSTV-Y]|9[ABCEGHJKVY])|P(0[ABCEGHJ-NPRSTV-Y]|1[ABCHLP]|2[ABN]|3[ABCEGLNPY]|4[NPR]|5[AEN]|6[ABC]|7[ABCEGJKL]|8[NT]|9[AN])|R(0[ABCEGHJ-M]|1[ABN]|2[CEGHJ-NPRV-Y]|3[ABCEGHJ-NPRSTV-Y]|4[AHJKL]|5[AGH]|6[MW]|7[ABCN]|8[AN]|9[A])|S(0[ACEGHJ-NP]|2[V]|3[N]|4[AHLNPRSTV-Z]|6[HJKVWX]|7[HJ-NPRSTVW]|9[AHVX])|T(0[ABCEGHJ-MPV]|1[ABCGHJ-MPRSV-Y]|2[ABCEGHJ-NPRSTV-Z]|3[ABCEGHJ-NPRZ]|4[ABCEGHJLNPRSTVX]|5[ABCEGHJ-NPRSTV-Z]|6[ABCEGHJ-NPRSTVWX]|7[AENPSVXYZ]|8[ABCEGHLNRSVWX]|9[ACEGHJKMNSVWX])|V(0[ABCEGHJ-NPRSTVWX]|1[ABCEGHJ-NPRSTV-Z]|2[ABCEGHJ-NPRSTV-Z]|3[ABCEGHJ-NRSTV-Y]|4[ABCEGK-NPRSTVWXZ]|5[ABCEGHJ-NPRSTV-Z]|6[ABCEGHJ-NPRSTV-Z]|7[ABCEGHJ-NPRSTV-Y]|8[ABCGJ-NPRSTV-Z]|9[ABCEGHJ-NPRSTV-Z])|X(0[ABCGX]|1[A])|Y(0[AB]|1[A]))[ ]?[0-9]{1}[ABCEGHJ-NPRSTV-Z]{1}[0-9]{1}$

isValidZipCode

2008-08-09T07:47:00.000-07:00

Another week, another validation function. Last week was a little long, so this week we'll do a bit shorter one: validating a United States ZIP code. The pattern is simple enough that I don't think an explanation is warranted.

ASP

function isValidZIPCode(zipCode)
dim regEx
set regEx = new RegExp
with regEx
.IgnoreCase = True
.Global = True
.Pattern = "^[0-9]{5}(-[0-9]{4})?$"
end with
if regEx.Test(trim(CStr(zipCode))) then
isValidZipCode = True
else
isValidZipCode = False
end if
set regEx = nothing
end function

PHP

function isValidZIPCode($zipCode)
{
return (preg_match("/^[0-9]{5}(-[0-9]{4})?$/i", trim($zipCode)) > 0) ? true : false;
}

isValidEmail

2008-08-02T06:46:00.000-07:00

This week we're going to build on the regular expression we wrote last week to validate e-mail addresses. What do IP addresses have to do with e-mail addresses? Just like domain names map to IP addresses, so also the domain part of an e-mail address can be substituted with an IP address, so instead of person@example.com you could have person@192.168.1.1

ASP

function isValidEmail(email)
dim regEx
dim result
set regEx = new RegExp
with regEx
.IgnoreCase = True
.Global = True
.Pattern = "^[^@]{1,64}@[^@]{1,255}$"
end with
result = false
' Test length.
if regEx.Test(email) then
regEx.Pattern = "^((([\w\+\-]+)(\.[\w\+\-]+)*)|(\"[^(\\|\")]{0,62}\"))@(([a-zA-Z0-9\-]+\.)+([a-zA-Z0-9]{2,})|\[?([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}\]?)$"
' Test syntax.
if regEx.Test(email) then
result = true
end if
end if
isValidEmail = result
set regEx = nothing
end function

PHP

function isValidEmail($email)
{
$lengthPattern = "/^[^@]{1,64}@[^@]{1,255}$/";
$syntaxPattern = "/^((([\w\+\-]+)(\.[\w\+\-]+)*)|(\"[^(\\|\")]{0,62}\"))@(([a-zA-Z0-9\-]+\.)+([a-zA-Z0-9]{2,})|\[?([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}\]?)$/";
return ((preg_match($lengthPattern, $email) > 0) && (preg_match($syntaxPattern, $email) > 0)) ? true : false;
}

The validation is broken down into two steps: checking the length of each part, and checking the syntax of each part.

^[^@]{1,64}@[^@]{1,255}$

The part before the @ symbol is called the local part, and cannot exceed 64 characters. The part after the @ symbol is called the domain part, and cannot exceed 255 characters.

^((([\w\+\-]+)(\.[\w\+\-]+)*)|(\"[^(\\|\")]{0,62}\"))@(([a-zA-Z0-9\-]+\.)+([a-zA-Z0-9]{2,})|\[?([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}\]?)$

In the check for syntax, the local part is validated by ((([\w\+\-]+)(\.[\w\+\-]+)*)|(\"[^(\\|\")]{0,62}\")). This is actually two patterns separated by the pipe character. The first, (([\w\+\-]+)(\.[\w\+\-]+)*), allows letters, numbers, the plus sign, and the hyphen (or minus sign if you prefer). It also allows periods, but not as the first or last character. The second, (\"[^(\\|\")]{0,62}\"), allows just about anything, provided the local part is enclosed in quotation marks (which is valid, but you'll probably never encounter it).

The domain part is validated by (([a-zA-Z0-9\-]+\.)+([a-zA-Z0-9]{2,})|\[?([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}\]?). Once again, this is two different patterns separated by the pipe character. The second pattern is our IP address checker from last week with optional enclosure in square brackets. The first pattern, ([a-zA-Z0-9\-]+\.)+([a-zA-Z0-9]{2,}), allows a slightly smaller range of characters (no plus signs or underscores), any number of subdomains, and a top-level domain of at least 2 characters (the minimum). Some regular expressions will impose a maximum of six characters on the top-level domain (the longest at the moment is .museum), but that wouldn't allow for longer top-level domains that could be created in the future.

isValidIP

2008-07-26T07:03:00.000-07:00

As promised, more regular expression fun. This week we're going to validate IP addresses. An IP address consists of four octets separated by periods. A lazy person might be inclined to use a regular expression of \d{1,3} for each octet, but that would allow numbers larger than 255. A more complex expression is needed: ([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1}).

This expression consists of three parts separated by the pipe character "|". The first part, [1]?\d{1,2}, matches numbers between 0 and 199. The second part, 2[0-4]{1}\d{1}, matches numbers between 200 and 249. The third part, 25[0-5]{1}, matches numbers between 250 and 255. We will repeat this pattern four times, once for each octet, and separate with periods.

ASP

function isValidIP(ip)
dim regEx
set regEx = new RegExp
with regEx
.IgnoreCase = True
.Global = True
.Pattern = "^([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}$"
end with
if regEx.Test(trim(CStr(ip))) then
isValidIP = true
else
isValidIP = false
end if
set regEx = nothing
end function

PHP

function isValidIP($ip)
{
$pattern = "/^([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})(\.([1]?\d{1,2}|2[0-4]{1}\d{1}|25[0-5]{1})){3}$/";
return (preg_match($pattern, $ip) > 0) ? true : false;
}

Next week we're going to build on this pattern to validate something else. I wonder what that could be?

isAlpha(Numeric)

2008-07-19T12:58:00.000-07:00

We're going to take a break from math-related functions for a few weeks (yay!) and play with regular expressions. Regular expressions are more powerful and faster than old-fashioned string parsing.

Both ASP and PHP have a function for checking if something is numeric. How about a function for checking if something is alphabetical?

ASP

function isAlpha(someString)
dim regEx
set regEx = new RegExp
with regEx
.Global = true
.IgnoreCase = true
.Pattern = "[A-Z\s_]"
end with
if regEx.test(someString) then
isAlpha = true
else
isAlpha = false
end if
set regEx = nothing
end function

PHP

function is_alpha($someString)
{
return (preg_match("/[A-Z\s_]/i", $someString) > 0) ? true : false;
}

The test pattern we are using above will allow letters of the alphabet, the underscore character, and whitespace characters. With a small tweak to the test pattern, we can also write a function to check if a string is alphanumeric.

ASP

function isAlphaNumeric(someString)
dim regEx
set regEx = new RegExp
with regEx
.Global = true
.IgnoreCase = true
.Pattern = "[\w\s.]"
end with
if regEx.test(someString) then
isAlphaNumeric = true
else
isAlphaNumeric = false
end if
set regEx = nothing
end function

PHP

function is_alphanumeric($someString)
{
return (preg_match("/[\w\s.]/i", $someString) > 0) ? true : false;
}

The \w switch in the pattern includes the 26 letters of the alphabet plus the numbers zero through nine.

More regular expression fun next week!

Fibonacci numbers

2008-07-12T07:55:00.000-07:00

The Fibonacci numbers have many applications in computer programming. Today we're going to write a function that returns individual numbers from the Fibonacci sequence.

ASP

function fib(x)
dim fibArray()
redim fibArray(x)
fibArray(0) = 0
fibArray(1) = 1
for i = 2 to x
fibArray(i) = fibArray(i - 1) + fibArray(i - 2)
next
fib = fibArray(x)
end function

PHP

function fib($x)
{
$fibArray[0] = 0;
$fibArray[1] = 1;
for($i = 2; $i <= $x; $i++)
{
$fibArray[$i] = $fibArray[$i - 1] + $fibArray[$i - 2];
}
return $fibArray[$x];
}

So, for example, fib(8) will return 21, because the Fibonacci sequence is 1, 1, 2, 3, 5, 8, 13, 21, 34, 55...

Fermat numbers

2008-07-05T07:04:00.000-07:00

Today we're going to write a function to generate Fermat numbers. This could be useful if you want to write your own pseudo-random number generator.

ASP

function fermat(x)
fermat = 2^2^x + 1
end function

PHP

function fermat($x)
{
return 2^2^$x + 1;
}

AM/PM

2008-06-21T07:36:00.000-07:00

To those of you who have been bored by the recent string of math-related articles, I apologize. I still have a lot of math-related functions to share with you, but I do have other things to share with you as well, such as validation functions, string functions, and datetime functions. This week we'll take a look at one of those datetime functions.

In ASP, time values are normally in the format HH:MM:SS followed by AM or PM. Quite often, we don't want to include the seconds portion, so we extract the hours and minutes using the Hour() and Minute() functions respectively. Unfortunately, there is no quick function for extracting the AM/PM. Let's do something about that right now.

function ampm(someTime)
if hour(someTime) < 12 then
ampm = "AM"
else
ampm = "PM"
end if
end function

Now we can do stuff like this:
Hour(someTime) & ":" & Minute(someTime) & " " & ampm(someTime)

Those of you who are PHP programmers are hopefully aware that the same result can be achieved in PHP using the built-in date() function and specifying the letter A or a in the format string for uppercase or lowercase respectively:
date("g:i A", $timestamp)

View this code on Snipplr

Factorial

2008-06-14T06:56:00.000-07:00

This week we're going to delve into some discrete math, starting with factorial. The factorial of a number is the product of that number and all the numbers smaller than it. For example, the factorial of 3 is 1 x 2 x 3 = 6.

ASP

function factorial(x)
dim result
result = 1
if x > 1 then
for i = 2 to x
result = result * i
next
end if
factorial = result
end function

PHP

function factorial($x)
{
$result = 1;
if ($x > 1)
{
for ($i = 2; $i <= $x; $i++)
{
$result *= $i;
}
}
return $result;
}

Now that we have a function for factorial, we can also do combinatorial. Combinatorial tells us the number of combinations, without regard to order, of y items that can be made from a pool of x items.

ASP

function combinatorial(x, y)
if (x >= y) and (y > 0) then
combinatorial = factorial(x) / factorial(y) / factorial(x - y)
else
combinatorial = 0
end if
end function

PHP

function combinatorial($x, $y)
{
return (($x >= $y) && ($y > 0)) ? factorial($x) / factorial($y) / factorial($x - $y) : 0;
}

We can also get the number of permutations of y items that can be made from a pool of x items.

ASP

function permutations(x, y)
permutations = factorial(x) / factorial(x - y)
end function

PHP

function permutations($x, $y)
{
return factorial($x) / factorial($x - $y);
}

Pythagorean Theorem

2008-06-07T07:59:00.000-07:00

When you're dealing with right-angled triangles, trigonometry is not required to calculate the length of the hypotenuse. Our PHP programmers friends have a function called hypot() which solves for c in the equation: a^2 + b^2 = c^2

function hypot(a, b)
hypot = sqr(a^2 + b^2)
end function

Using the classic 3-4-5 triangle as an example, for a = 3 and b = 4, the function will return 5.

View this code on Snipplr

Degrees and Radians

2008-05-31T06:50:00.000-07:00

When you were learning trigonometry, you probably measured angles in degrees. But in calculus, angles are measured in radians (search for "degrees vs. radians" on Google for the reasons). Being able to convert between these two units might be handy. PHP provides two functions for this purpose, but no such luck in ASP. As usual, we're going to write our own.

Radians is heavily based on my favorite number, pi. We're going to need this number in our calculations, so make sure to define a constant for it.

Const M_PI = 3.14159265358979323846

And now the functions themselves...

function deg2rad(x)
deg2rad = x * M_PI / 180
end function
function rad2deg(x)
rad2deg = x * 180 / M_PI
end function

View this code on Snipplr

Euclid's Algorithm

2008-05-24T06:31:00.000-07:00

Euclid's algorithm is one of the oldest, known by ancient Greeks like Aristotle. You might remember it from elementary school when you had to find things like greatest common factor/divisor and least common multiple. Greatest common factor/divisor allowed you to reduce fractions like 4/12 to 1/3. Least common multiple allowed you to add and subtract fractions that had different denominators.

There is more than one way to implement this algorithm. The original involved iterative subtraction. This was later improved upon with iterative modulo division. Another method, the one I'll be using here, is recursion.

ASP

function gcd(byVal a, byVal b)
a = abs(a)
b = abs(b)
if a = 0 then
gcd = b
elseif b = 0 then
gcd = a
elseif a > b then
gcd = gcd(b, a mod b)
else
gcd = gcd(a, b mod a)
end if
end function
function lcm(byVal a, byVal b)
a = abs(a)
b = abs(b)
if a > b then
lcm = (b / gcd(a, b)) * a
else
lcm = (a / gcd(a, b)) * b
end if
end function

PHP

function gcd($a, $b)
{
$a = abs($a);
$b = abs($b);
if ($a == 0)
{
return $b;
}
elseif ($b == 0)
{
return $a;
}
elseif ($a > $b)
{
return gcd($b, $a % $b);
}
else
{
return gcd($a, $b % $a);
}
}
function lcm($a, $b)
{
$a = abs($a);
$b = abs($b);
if ($a > $b)
{
return ($b / gcd($a, $b)) * $a;
}
else
{
return ($a / gcd($a, $b)) * $b;
}
}

Euclid's algorithm is not always the fastest, but it is the simplest. A better algorithm was devised by 20th century mathematician Dick Lehmer. Another 20th century mathematician, Josef Stein, devised a specialized algorithm for computers which uses bit shifting. Note, however, that the performance improvement of these more modern algorithms varies depending on the CPU and size of the numbers involved. In some cases, Euclid is actually faster.

Update

2008-05-19T12:48:00.000-07:00

I've updated my Leap Years article with more elegant PHP solutions thanks to Jim Mayes.

I discovered his feedback via a web site called Snipplr, where I've been uploading all the code examples from this blog. All the previous code examples are still available here on the blog, but I'm considering posting future code examples on Snipplr only and linking to them from the blog, because it takes a ridiculous amount of time to format the code examples to display nicely on the blog. I think it will depend on the length of the example; I don't mind reformatting short examples, but I've got some longer ones that I'd rather not.

Anyways, you can view all my code snippets from my Snipplr profile. There are also some bonus things in there which are outside the scope of this blog (eg. Windows registry tweaks). I've also added this link to the sidebar so that it will be easy to find in the future when this post disappears off the front page.

Ceiling and Floor

2008-05-17T08:04:00.000-07:00

In mathematics, there are two elementary special functions called ceiling() and floor() which allow us to round up or down, respectively, to the nearest whole number. These functions exist natively in PHP, but not in ASP. They are handy in situations where you want to force a number like 15.8 to round down to 15, but the round() function rounds it up to 16 according to the standard rules for rounding.

ASP

function floor(x)
dim temp
temp = round(x)
if temp > x then
temp = temp - 1
end if
floor = temp
end function
function ceil(x)
dim temp
temp = round(x)
if temp < x then
temp = temp + 1
end if
ceil = temp
end function

Tractive Effort

2008-05-10T07:13:00.000-07:00

This week is another short, fun snippet of code. We're going to calculate the tractive effort of a steam locomotive. Useless to most people, but I've got a large project where I'll be using it myself.

ASP

function TractiveEffort(cylinderDiameter, stroke, pressure, wheelDiameter)
TractiveEffort = cylinderDiameter ^ 2 * stroke * pressure * 0.85 / wheelDiameter
end function

PHP

function $tractiveEffort($cylinderDiameter, $stroke, $pressure, $wheelDiameter)
{
return $cylinderDiameter ^ 2 * $stroke * $pressure * 0.85 / $wheelDiameter;
}

It should be noted that the formula only applies to non-compound steam locomotives. Locomotives with multiple cylinders are more complex.

Base Conversion

2008-05-03T07:47:00.000-07:00

Most of the modern world uses a base-10 number system. It's the easiest to work with. However, when it comes to computer systems, we use a few different number systems too. Base-2, or binary, is the basis of data storage and transmission; a bit is either on or off. We also use Base-8, or octal; each byte contains 8 bits. Last but not least is Base-16, or hexadecimal.

Under some circumstances, we might need to convert between these different number systems. ASP provides a pathetic two functions for this purpose: hex(), which converts from base-10 (decimal) to base-16 (hexadecimal), and oct() which converts from decimal to octal. PHP provides equivalent functions dechex() and decoct(), as well as additional functions decbin() for converting from decimal to binary, bindec() for converting from binary to decimal, hexdec() for converting from hexadecimal to decimal, and octdec() for converting from octal to decimal.

It would be nice to extend ASP to support these four additional functions. When I started doing that, I noticed a pattern in the formulae. All the functions that converted from decimal were fairly similar, and all the functions that converted to decimal were also fairly similar. So I abstracted the calculations out into their own functions and simplified my code.

ASP

' Convert from binary to decimal.
function bindec(bin)
bindec = toDecimal(bin, 2)
end function
' Convert from decimal to binary
function decbin(dec)
decbin = fromDecimal(dec, 2)
end function
' Convert from decimal to hexadecimal.
function dechex(dec)
' Assume that built-in hex() function is faster.
dechex = hex(dec)
end function
' Convert from decimal to octal.
function decoct(dec)
' Assume that built-in oct() function is faster.
decoct = oct(dec)
end function
' Convert from hexadecimal to decimal.
function hexdec(hex)
hexdec = toDecimal(hex, 16)
end function
' Convert from octal to decimal.
function octdec(oct)
octdec = toDecimal(oct, 8)
end function

Before we get into the underlying fromDecimal() and toDecimal() functions, some things need to be said. The lowest possible base is 2, so if the user tries to specify a base smaller than 2, we will change it to 2. Likewise, there is a practical upper limit of base 36. Beyond that, things get more complicated, so any base higher than 36 will be changed to 36 to prevent the function from going out of bounds and returning bad data.

ASP

function toDecimal(value, radix)
dim result
dim digit
result = 0
' Prevent radix from going out of bounds.
if radix < 2 then
radix = 2
elseif radix > 36 then
radix = 36
end if
for i = 1 to Len(value)
digit = Mid(value, i, 1)
' Convert letters to numbers.
if not isNumeric(digit) then
' The letter A in any base is equal to 10 in decimal.
' The ASCII value of A is 65, so subtract 55 from the ASCII value to obtain the decimal value.
digit = Asc(UCase(digit)) - 55
else
digit = CInt(digit)
end if
' Return zero if any digit is out of bounds for the radix.
if digit >= radix then
result = 0
exit for
end if
result = result + (digit * radix ^ (Len(value) - i))
next
toDecimal = result
end function
function fromDecimal(value, radix)
dim result
dim digit
result = 0
' Prevent radix from going out of bounds.
if radix < 2 then
radix = 2
elseif radix > 36 then
radix = 36
end if
' Check for invalid input.
if isNumeric(value) then
' Inputted value appears to be base 10. OK to proceed.
do until value = 0
digit = value Mod radix
if digit > 9 then
digit = Chr(digit + 55)
end if
result = CStr(digit) & result
value = value \ radix
loop
else
' Inputted value was NOT base 10.
result = 0
end if
fromDecimal = result
end function

It would be even better if we could easily convert between two bases where neither one is decimal. Also, it would be nice to have a unified interface. We can achieve both with one function, base_convert(), which is also present in PHP.

ASP

function base_convert(value, sourceRadix, targetRadix)
if sourceRadix = targetRadix then
' If source radix and target radix are equal, don't waste time converting.
baseConv = value
elseif sourceRadix = 10 then
' If source radix is decimal, skip converting to decimal.
baseConv = fromDecimal(value, targetRadix)
elseif targetRadix = 10 then
' If target radix is decimal, skip converting from decimal.
baseConv = toDecimal(value, sourceRadix)
else
' Convert to decimal, and then from decimal.
baseConv = fromDecimal(toDecimal(value, sourceRadix), targetRadix)
end if
end function

I leave you with the following potential exercises:

From base 37 to 62, the lowercase letters of the Latin alphabet are used, but special handling would need to be added for them. The ASCII value for Z is 90. The ASCII value for a is 97. There are six other characters in between.
Base64 encoding begins with the uppercase letters A-Z, followed by a-z, followed by 0-9, followed by + and /. If you want to add Base64 support, separate functions would be wise, but could still be tied into the base_convert() wrapper.

Immediate If

2008-04-26T10:12:00.000-07:00

Visual Basic programmers have a function at their disposal called IIf(), which is an abbreviation for Immediate If.

Example

result = IIf(2 + 2 = 5, "Correct", "Wrong")

The iif() function is sometimes more convenient than a full-blown if...then...else... control structure. Oddly enough, the function does not exist in VBScript.

Our PHP programmer friends have a superior equivalent, the ternary operator.

Example

$result = (2 + 2 = 5) ? 'Correct' : 'Wrong';

Unfortunately we can't recreate the ternary operator in ASP, but we can recreate the iif() function.

ASP

function IIf(expression, truecondition, falsecondition)
if cbool(expression) then
IIf = truecondition
else
IIf = falsecondition
end if
end function

Proper Case

2008-04-19T08:25:00.000-07:00

Both ASP and PHP have handy functions for forcing characters in a string to be all uppercase or all lowercase, but what about proper case? Proper case is used for names of people, titles of songs or movies, etc. The first letter in each word is capitalized, and the other letters are lowercase.

PHP has a built-in function for this, but the usage is slightly different and the name of the function is inconsistent, so we're going to write a facade function.

PHP

function strtoproper($someString)
{
return ucwords(strtolower($someString));
}

ASP doesn't have a function for this, though full-blown Visual Basic does. We're going to duplicate that functionality, and make a few improvements. Consider names like McDonald and O'Brien. An ordinary proper case function would not handle these properly. We're going to use a regular expression to find these situations and handle them appropriately.

ASP

function PCase(someString)
dim position
dim space
dim result
dim regEx
position = 1
set regEx = new RegExp
regEx.Pattern = "^(Mc[A-Z]{1}[A-Za-z]|O\'[A-Z]{1}[A-Za-z]|Mac[A-Z]{1}[A-Za-z])"
' Loop through the string checking for spaces.
do while InStr(position, someString, " ", 1) <> 0
' Find the position of the next space.
space = InStr(position, someString, " ", 1)
' Capitalize (and append to our output) the first character after the space which was handled by the previous run through the loop.
result = result & UCase(Mid(someString, position, 1))
' Check for situations like McDonald or O'Brien.
if not regEx.Test(Mid(someString, position, space - position)) then
' Lowercase (and append to our output) the rest of the string up to and including the current space.
result = result & LCase(Mid(someString, position + 1, space - position))
else
if Left(Mid(someString, position), 3) = "Mac" then
' Leave the next three characters intact.
result = result & Mid(someString, position + 1, 3)
' Append the rest of the string.
result = result & LCase(Mid(someString, position + 4, space - position + 4))
else
' Leave the next two characters intact.
result = result & Mid(someString, position + 1, 2)
' Append the rest of the string.
result = result & LCase(Mid(someString, position + 3, space - position + 3))
end if
end if
position = space + 1
loop
' Capitalize the first character of the last word after the final space (or the only word if there were no spaces).
result = result & UCase(Mid(someString, position, 1))
' Check for situations like McDonald or O'Brien.
if not regEx.Test(Mid(someString, position)) then
' Lowercase (and append to our output) the rest of the string up to and including the current space.
result = result & LCase(Mid(someString, position + 1))
else
if Left(Mid(someString, position), 3) = "Mac" then
' Leave the next three characters intact.
result = result & Mid(someString, position + 1, 3)
' Append the rest of the string.
result = result & LCase(Mid(someString, position + 4))
else
' Leave the next two characters intact.
result = result & Mid(someString, position + 1, 2)
' Append the rest of the string.
result = result & LCase(Mid(someString, position + 3))
end if
end if
set regEx = Nothing
PCase = result
end function

Ordinal Numbers

2008-04-12T08:52:00.000-07:00

This week we're going to write a function to turn a cardinal integer into an ordinal number (eg. 4 becomes 4th). This is mostly useful when generating a page to display to a visitor.

ASP

function ordinal(ByVal cardinal)
cardinal = CStr(cardinal)
if Right(cardinal, 1) = "1" and Right(cardinal, 2) <> "11" then
ordinal = cardinal & "st"
elseif Right(cardinal, 1) = "2" and Right(cardinal, 2) <> "12" then
ordinal = cardinal & "nd"
elseif Right(cardinal, 1) = "3" and Right(cardinal, 2) <> "13" then
ordinal = cardinal & "rd"
else
ordinal = cardinal & "th"
end if
end function

PHP

function ordinal($cardinal)
{
if (substr($cardinal, -1, 1) == 1 && substr($cardinal, -2, 2) != 11)
{
return ($cardinal . 'st');
}
elseif (substr($cardinal, -1, 1) == 2 && substr($cardinal, -2, 2) != 12)
{
return ($cardinal . 'nd');
}
elseif (substr($cardinal, -1, 1) == 3 && substr($cardinal, -2, 2) != 13)
{
return ($cardinal . 'rd');
}
else
{
return ($cardinal . 'th');
}
}

Force SSL

2008-04-05T07:48:00.000-07:00

If your web site requires visitors to enter private information, like their credit card number, or even just a username and password, you're hopefully using SSL to secure the transmission. But providing SSL is not enough, because visitors can still access your site without SSL. When a visitor navigates to a page where they are entering private information, we want to enforce that their data is protected by SSL.

Our PHP programmer friends can do this via an htaccess file:

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}

But for those of us stuck using ASP, we don't have this luxury. We can achieve the same result with some code.

sub forceSSL()
dim secureURL
if UCase(Request.ServerVariables("HTTPS")) = "OFF" then
secureURL = "https://" & Request.ServerVariables("SERVER_NAME") & Request.ServerVariables("HTTP_URL")
if Request.ServerVariables("QUERY_STRING") <> "" then
secureURL = secureURL & "?" & Request.ServerVariables("QUERY_STRING")
end if
Response.Redirect secureURL
end if
end sub

There are some things here worth noting. In both the htaccess example and the ASP example, we are checking if HTTPS is off. Some people will instead check if traffic is coming from port 80, the standard HTTP port, or not coming from 443, the standard HTTPS port. Checking port numbers is not the best solution because the server administrator can set up HTTP and HTTPS to run on different ports. It's also worth noting that the above ASP example preserves QueryString variables, if any are being passed. Most other examples I've seen on the Internet ignore the QueryString variables, which leads to navigation problems.

With this subroutine in your arsenal, just call it at the top of any page you want to secure.

Finding your Star Wars name

2008-03-29T08:05:00.000-07:00

It's high time we did something fun. We're going to write a function that determines a person's Star Wars name.

ASP

function starwarsname(firstName, lastName, maidenName, city)
starwarsname = Left(firstName, 3) & LCase(Left(lastName, 2)) & " " & Left(maidenName, 2) & LCase(Left(city, 3))
end function

PHP

function starwarsname($firstName, $lastName, $maidenName, $city)
{
return substr($firstName, 0, 3) . strtolower(substr($lastName, 0, 2)) . " " . substr($maidenName, 0, 2) . strtolower(substr($city, 0, 3));
}

Calculating Easter

2008-03-22T08:31:00.000-07:00

It's Easter weekend, and as promised we're going to write a function to calculate when Easter occurs for a given year. Easter is a strange holiday in that it jumps around the calendar between March and April. This is because it is tied to the lunar cycle. Easter occurs on the first Sunday after the Paschal full moon.

ASP

function dateEaster(someYear)
Dim goldenNumber
Dim solarCorrection
Dim lunarCorrection
Dim paschalFullMoon
Dim dominicalNumber
Dim difference
Dim dayEaster
goldenNumber = (someYear Mod 19) + 1
if someYear <= 1752 then
' Julian calendar
dominicalNumber = (someYear + (someYear / 4) + 5) Mod 7
paschalFullMoon = (3 - (11 * goldenNumber) - 7) Mod 30
else
' Gregorian calendar
dominicalNumber = (someYear + (someYear / 4) - (someYear / 100) + (someYear / 400)) Mod 7
solarCorrection = (someYear - 1600) / 100 - (someYear - 1600) / 400
lunarCorrection = (((someYear - 1400) / 100) * 8) / 25
paschalFullMoon = (3 - 11 * goldenNumber + solarCorrection - lunarCorrection) Mod 30
end if
do until dominicalNumber > 0
dominicalNumber = dominicalNumber + 7
loop
do until paschalFullMoon > 0
paschalFullMoon = paschalFullMoon + 30
loop
if paschalFullMoon = 29 or (paschalFullMoon = 28 and goldenNumber > 11) then
paschalFullMoon = paschalFullMoon - 1
end if
difference = (4 - paschalFullMoon - dominicalNumber) Mod 7
if difference < 0 then
difference = difference + 7
end if
dayEaster = paschalFullMoon + difference + 1
if dayEaster < 11 then
' Easter occurs in March.
dateEaster = DateSerial(someYear, 3, dayEaster + 21)
else
' Easter occurs in April.
dateEaster = DateSerial(someYear, 4, dayEaster - 10)
end if
end function

PHP

function dateEaster($someYear)
{
$goldenNumber = fmod($someYear, 19) + 1;
if ($someYear <= 1752)
{
// Julian calendar
$dominicalNumber = fmod($someYear + ($someYear / 4) + 5, 7);
$paschalFullMoon = fmod(3 - (11 * $goldenNumber) - 7, 30);
}
else
{
// Gregorian calendar
$dominicalNumber = fmod($someYear + ($someYear / 4) - ($someYear / 100) + ($someYear / 400), 7);
$solarCorrection = ($someYear - 1600) / 100 - ($someYear - 1600) / 400;
$lunarCorrection = ((($someYear - 1400) / 100) * 8) / 25;
$paschalFullMoon = fmod(3 - 11 * $goldenNumber + $solarCorrection - $lunarCorrection, 30);
}
while ($dominicalNumber < 0)
{
$dominicalNumber += 7;
}
while ($paschalFullMoon < 0)
{
$paschalFullMoon += 30;
}
if ($paschalFullMoon == 29 || ($paschalFullMoon == 28 && $goldenNumber > 11))
{
$paschalFullMoon--;
}
$difference = fmod(4 - $paschalFullMoon - $dominicalNumber, 7);
if ($difference < 0)
{
$difference += 7;
}
$dayEaster = $paschalFullMoon + $difference + 1;
if ($dayEaster < 11)
{
// Easter occurs in March.
$dateEaster = mktime(0, 0, 0, 3, $dayEaster + 21, $someYear);
}
else
{
// Easter occurs in April.
$dateEaster = mktime(0, 0, 0, 4, $dayEaster - 10, $someYear);
}
return $dateEaster;
}

We can calculate the other ecclesiastical holidays by offsetting the date of Easter with the number of days between Easter and the holiday we're looking for.

ASP

function dateGoodFriday(someYear)
dateGoodFriday = DateAdd("d", -2, dateEaster(someYear))
end function
function datePalmSunday(someYear)
datePalmSunday = DateAdd("d", -7, dateEaster(someYear))
end function
function dateAshWednesday(someYear)
dateAshWednesday = DateAdd("d", -46, dateEaster(someYear))
end function
function dateAscensionDay(someYear)
dateAscensionDay = DateAdd("d", 39, dateEaster(someYear))
end function
function datePentecost(someYear)
datePentecost = DateAdd("d", 49, dateEaster(someYear))
end function

PHP

function dateGoodFriday($someYear)
{
$easter = getDate(dateEaster($someYear));
return mktime(0, 0, 0, $easter[mon], $easter[mday] - 2, $easter[year]);
}
function datePalmSunday($someYear)
{
$easter = getDate(dateEaster($someYear));
return mktime(0, 0, 0, $easter[mon], $easter[mday] - 7, $easter[year]);
}
function dateAshWednesday($someYear)
{
$easter = getDate(dateEaster($someYear));
return mktime(0, 0, 0, $easter[mon], $easter[mday] - 46, $easter[year]);
}
function dateAscensionDay($someYear)
{
$easter = getDate(dateEaster($someYear));
return mktime(0, 0, 0, $easter[mon], $easter[mday] + 39, $easter[year]);
}
function datePentecost($someYear)
{
$easter = getDate(dateEaster($someYear));
return mktime(0, 0, 0, $easter[mon], $easter[mday] + 49, $easter[year]);
}

Roman Numerals, Part 2

2008-03-15T12:08:00.000-07:00

Last week we converted integers into Roman numerals, and I promised this week we would write a function to do the opposite. Part of the difficulty in working with Roman numerals is the subtractive notation. The number four can be written as IV or IIII; writing it as IV is the subtractive notation. When I precedes V, it means one less than five; if you reverse the two (VI), it means one more than five.

To make our life easier, we want to expand the subtractive notation so that each numeral is equal to its value. While we're at it, we'll also write a function to compress Roman numerals back in subtractive notation.

ASP

function roman_expand(ByVal roman)
roman = replace(roman, "CM", "DCCCC")
roman = replace(roman, "CD", "CCCC")
roman = replace(roman, "XC", "LXXXX")
roman = replace(roman, "XL", "XXXX")
roman = replace(roman, "IX", "VIIII")
roman = replace(roman, "IV", "IIII")
roman_expand = roman
end function
function roman_compress(ByVal roman)
roman = replace(roman, "DCCCC", "CM")
roman = replace(roman, "CCCC", "CD")
roman = replace(roman, "LXXXX", "XC")
roman = replace(roman, "XXXX", "XL")
roman = replace(roman, "VIIII", "IX")
roman = replace(roman, "IIII", "IV")
roman_compress = roman
end function

PHP

function roman_expand($roman)
{
$roman = str_replace("CM", "DCCCC", $roman);
$roman = str_replace("CD", "CCCC", $roman);
$roman = str_replace("XC", "LXXXX", $roman);
$roman = str_replace("XL", "XXXX", $roman);
$roman = str_replace("IX", "VIIII", $roman);
$roman = str_replace("IV", "IIII", $roman);
return $roman;
}
function roman_compress($roman)
{
$roman = str_replace("DCCCC", "CM", $roman);
$roman = str_replace("CCCC", "CD", $roman);
$roman = str_replace("LXXXX", "XC", $roman);
$roman = str_replace("XXXX", "XL", $roman);
$roman = str_replace("VIIII", "IX", $roman);
$roman = str_replace("IIII", "IV", $roman);
return $roman;
}

These expand and compress functions would be essential if you wanted to write some functions to actually perform arithmetic on Roman numerals, and although on paper Roman addition is fairly straightforward, an implementation of it in code performs more poorly than simply converting the Roman numeral back into an integer and using the built-in math operators.

The following ASP function requires the InstrCount function from my previous post.

ASP

function arabic(ByVal roman)
Dim result
result = 0
' Remove subtractive notation.
roman = roman_expand(roman)
' Calculate for each numeral.
result = result + InstrCount(roman, "M") * 1000
result = result + InstrCount(roman, "D") * 500
result = result + InstrCount(roman, "C") * 100
result = result + InstrCount(roman, "L") * 50
result = result + InstrCount(roman, "X") * 10
result = result + InstrCount(roman, "V") * 5
result = result + InstrCount(roman, "I")
end function

PHP

function arabic($roman)
{
$result = 0;
// Remove subtractive notation.
$roman = roman_expand($roman);
// Calculate for each numeral.
$result += substr_count($roman, 'M') * 1000;
$result += substr_count($roman, 'D') * 500;
$result += substr_count($roman, 'C') * 100;
$result += substr_count($roman, 'L') * 50;
$result += substr_count($roman, 'X') * 10;
$result += substr_count($roman, 'V') * 5;
$result += substr_count($roman, 'I');
return $result;
}

Although I don't have code for you to actually add two Roman numerals together, I will tell you how to do it. For this example, we will add the numerals XIV and VII. First we must remove the subtractive notation, so XIV becomes XIIII and VII stays as it is. On paper we would then concatenate the two together and sort them.

XIIII + VII = XIIIIVII = XVIIIIII

We already have a concatenation operator, but we would need to write a custom sorting function for Roman numerals. If we're going to go that much trouble, it might be better to just build a new string by counting the number of each numeral in the two strings we are given. This would allow us to handle the situation above where we now have six I's. Our next step is to combine similar numerals that are equal to the next larger numeral.

XVIIIIII = XVVI = XXI

In code, it would be best to start with the smallest numeral, I, and work our way towards the largest numeral.

Subtraction of Roman numerals involves expanding and cancelling until there is only one number left.

XIV - VI = XIIII - VI = XIII - V = VVIII - V = VIII

I leave it up to you to research how to perform multiplication and division of Roman numerals, and whether or not you want to write functions for Roman arithmetic. Such functions would not be useful in production code, but writing them would be a good exercise, and it would be interesting to compare the runtimes with conversion back to Arabic followed by a conversion to Roman again.

Next weekend is Easter, so we'll be writing code to calculate when Easter and its related holidays (Good Friday, Pentecost, etc.) occur for any given year.

InstrCount()

2008-03-12T12:01:00.000-07:00

This is a special mid-week edition of Reusable Code. While preparing this weekend's edition, I discovered that for the ASP examples we would need another utility function that is useful outside of working with Roman numerals. I feel it important enough to have it's own post, but I don't want to delay the upcoming posts.

ASP programmers are probably familiar with the Instr() function. It returns the location of one string within another. Sometimes you want to know how many times one string occurs within another. PHP programmers have a built-in function called substr_count() which can do this. We're going to write our own function in ASP to duplicate some of this functionality.

function InstrCount(haystack, needle)
if needle <> "" then
InstrCount = UBound(Split(haystack, needle))
end if
end function

It's fairly self-explanatory, but just in case you're not familiar with the Split() function... We are splitting the string into an array, using the search string (needle) as our delimiter. The upper bound of the array gives us the number of needles in our haystack.

Why didn't I call the function substr_count() to match PHP? Normally I do like to have things consistent between languages because it makes it easier for people to go from one to the other, but in this particular case, the PHP function substr_count has two optional arguments. Since ASP does not support optional arguments (at least not the way you would expect), I went with a name more similar to the complementary Instr() function.

Roman Numerals, Part 1

2008-03-08T13:55:00.000-08:00

This weekend we're going to write a function to convert an integer into a Roman numeral, because storing Roman numerals in a database as strings is not cool.

ASP

function roman(ByVal arabic)
Dim ones
Dim tens
Dim hundreds
Dim thousands
ones = Array("", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX")
tens = Array("", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC")
hundreds = Array("", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM")
thousands = Array("", "M", "MM", "MMM", "MMMM")
if arabic > 4999 then
' For large numbers (five thousand and above), a bar is placed above a base numeral to indicate multiplication by 1000.
' Since it is not possible to illustrate this in plain ASCII, this function will refuse to convert numbers above 4999.
Err.Clear
Err.Raise 9
elseif arabic = 0 then
' About 725, Bede or one of his colleagues used the letter N, the initial of nullae,
' in a table of epacts, all written in Roman numerals, to indicate zero.
roman = "N"

else
roman = thousands((arabic - (arabic mod 1000)) / 1000)
arabic = arabic mod 1000
roman = roman & hundreds((arabic - (arabic mod 100)) / 100)
arabic = arabic mod 100
roman = roman & tens((arabic - (arabic mod 10)) / 10)
arabic = arabic mod 10
roman = roman & ones((arabic - (arabic mod 1)) / 1)
arabic = arabic mod 1
end if
end function

PHP

function roman($arabic)
{
$ones = Array("", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX");
$tens = Array("", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC");
$hundreds = Array("", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM");
$thousands = Array("", "M", "MM", "MMM", "MMMM");
if ($arabic > 4999)
{
// For large numbers (five thousand and above), a bar is placed above a base numeral to indicate multiplication by 1000.
// Since it is not possible to illustrate this in plain ASCII, this function will refuse to convert numbers above 4999.
die("Cannot represent numbers larger than 4999 in plain ASCII.");
}
elseif ($arabic == 0)
{
// About 725, Bede or one of his colleagues used the letter N, the initial of nullae,
// in a table of epacts, all written in Roman numerals, to indicate zero.
return "N";
}
else
{
$roman = $thousands[($arabic - fmod($arabic, 1000)) / 1000];
$arabic = fmod($arabic, 1000);
$roman .= $hundreds[($arabic - fmod($arabic, 100)) / 100];
$arabic = fmod($arabic, 100);
$roman .= $tens[($arabic - fmod($arabic, 10)) / 10];
$arabic = fmod($arabic, 10);
$roman .= $ones[($arabic - fmod($arabic, 1)) / 1];
$arabic = fmod($arabic, 1);
return $roman;
}
}

You may have noticed in the PHP example that I used the fmod() function instead of the % operator. That was a clue that you might want to add support for floating point integers. You can learn how to represent fractions from the Wikipedia article on Roman numerals. Here's a couple of hints to get you started:

You will need another array to hold the numerals for the fractional values.
The fractional portion should be handled after the whole number portion has been converted and modularly divided out.
However, pre-check the rounding of the fraction before you start the conversion. If it rounds to a whole number, round it off before the conversion to prevent problems.

Next weekend, we're going to write some utility functions that will be useful for turning Roman numerals back into integers, or if you're feeling particularly crazy, performing mathematical calculations on Roman numerals. The weekend after that is Easter weekend, so we'll write a function to calculate Easter and the related holidays surrounding it.

Leap Years

2008-03-02T07:41:00.000-08:00

This year (2008) is a leap year, and this past week contained February 29. It seems only fitting that we talk about calculating leap years and what we can do with that information.

A leap year is always divisible by four, but not by one hundred unless it is also divisible by four hundred.

ASP

function isLeapYear(someYear)
if someYear Mod 4 = 0 and (someYear Mod 100 <> 0 or (someYear Mod 100 = 0 and someYear Mod 400 = 0)) then
isLeapYear = True
else
isLeapYear = False
end if
end function

PHP

function isLeapYear($someYear)
{
return date("L", strtotime($someYear . "-01-01"));
}

Now let's write a function to build on this which returns the number of days in a given month.

ASP

function MonthDays(someMonth, someYear)
select case someMonth
case 1, 3, 5, 7, 8, 10, 12
MonthDays = 31
case 4, 6, 9, 11
MonthDays = 30
case 2
if isLeapYear(someYear) then
MonthDays = 29
else
MonthDays = 28
end if
end select
end function

PHP

function MonthDays($someMonth, $someYear)
{
return date("t", strtotime($someYear . "-" . $someMonth . "-01"));
}

UPDATE: Thanks to Jim Mayes for showing me more elegant PHP solutions.

Temperature Conversion

2008-02-23T10:15:00.000-08:00

I promised we'd do something different this week, and that something different is temperature conversion. We're going to write some code to convert between Celsius, Fahrenheit, and Kelvin - the three most popular units of measurement for temperature.

ASP

function CelsiusToFahrenheit(temperature)
CelsiusToFahrenheit = (temperature * 9 / 5) + 32
end function
function CelsiusToKelvin(temperature)
CelsiusToKelvin = temperature + 273.15
end function
function FahrenheitToCelsius(temperature)
FahrenheitToCelsius = (temperature - 32) * 5 / 9
end function
function FahrenheitToKelvin(temperature)
FahrenheitToKelvin = (temperature - 32) * 5 / 9 + 273.15
end function
function KelvinToCelsius(temperature)
KelvinToCelsius = temperature - 273.15
end function
function KelvinToFahrenheit(temperature)
KelvinToFahrenheit = (temperature - 273.15) * 9 / 5 + 32
end function

PHP

function CelsiusToFahrenheit($temperature)
{
return ($temperature * 9 / 5) + 32;
}
function CelsiusToKelvin($temperature)
{
return $temperature + 273.15;
}
function FahrenheitToCelsius($temperature)
{
return ($temperature - 32) * 5 / 9;
}
function FahrenheitToKelvin($temperature)
{
return ($temperature - 32) * 5 / 9 + 273.15;
}
function KelvinToCelsius($temperature)
{
return $temperature - 273.15;
}
function KelvinToFahrenheit($temperature)
{
return ($temperature - 273.15) * 9 / 5 + 32;
}

You may have noticed that the conversion between Celsius and Kelvin is a simple addition or subtraction. I could have written the code such that some functions make use of other functions, but I decided to write each function to be self-sufficient in performing it's calculations. The reason for this is speed; calling an extra function would give a small performance hit. You could consider this contrary to how I wrote the trigonometry functions, but in those cases, the calculations were more complicated.

Ok, so now what? Let's write a facade function to make it easier to call the individual conversion functions.

ASP

function convertTemperature(temperature, originScale, targetScale)
' Return the input value for temperature if both scales are identical.
if UCase(originScale) = UCase(targetScale) then
convertTemperature = temperature
exit function
end if
Select Case UCase(originScale)
Case "CELSIUS"
Select Case UCase(targetScale)
Case "FAHRENHEIT"
convertTemperature = CelsiusToFahrenheit(temperature)
Case "KELVIN"
convertTemperature = CelsiusToKelvin(temperature)
End Select
Case "FAHRENHEIT"
Select Case UCase(targetScale)
Case "CELSIUS"
convertTemperature = FahrenheitToCelsius(temperature)
Case "KELVIN"
convertTemperature = FahrenheitToKelvin(temperature)
End Select
Case "KELVIN"
Select Case UCase(targetScale)
Case "CELSIUS"
convertTemperature = KelvinToCelsius(temperature)
Case "FAHRENHEIT"
convertTemperature = KelvinToFahrenheit(temperature)
End Select
End Select
end function

PHP

function convertTemperature($temperature, $originScale, $targetScale)
{
// Return the input value for temperature if both scales are identical.
if (strtoupper($originScale) == strtoupper($targetScale))
{
return $temperature;
}
else
{
switch (strtoupper($originScale))
{
case "CELSIUS":
switch (strtoupper($targetScale))
{
case "FAHRENHEIT":
return CelsiusToFahrenheit($temperature);
break;
case "KELVIN":
return CelsiusToKelvin($temperature);
break;
}
break;
case "FAHRENHEIT":
switch (strtoupper($targetScale))
{
case "CELSIUS":
return FahrenheitToCelsius($temperature);
break;
case "KELVIN":
return FahrenheitToKelvin($temperature);
break;
}
break;
case "KELVIN":
switch (strtoupper($targetScale))
{
case "CELSIUS":
return KelvinToCelsius($temperature);
break;
case "FAHRENHEIT":
return KelvinToFahrenheit($temperature);
break;
}
break;
}
}
}

Whew! The line wrapping makes it look uglier than it is, but you can copy-paste it into your code editor of choice and it will be formatted correctly there.

That's it for this week and for this topic. If you want to expand on this, you can add conversion functions for other temperature scales: Delisle, Newton, Rankine, Reaumur, and Romer. The formulas and information about each scale are available on Wikipedia.

Trigonometry, Part 3

2008-02-18T08:26:00.000-08:00

I was hoping to publish every Saturday, but this past Saturday I got sidetracked. So without further ado, I bring you the next installment in the trigonometry series of articles.

Each of the six basic trigonometric functions has an inverse function. The inverse functions for sine, cosine, and tangent (arcsine, arcosine, and arctangent, respectively) are already defined natively in PHP. In ASP, only the inverse function for tangent (arctangent) is defined, but we will create an adapter for it to be consistent with the abbreviation in PHP. We also need to define some constants that are already present in PHP but not in ASP.

ASP

Const M_PI = 3.14159265358979323846
Const M_PI_2 = M_PI / 2
function asin(x)
asin = atn(x / sqr(1 - x ^ 2))
end function
function acos(x)
acos = M_PI_2 - asin(x)
end function
function atan(x)
atan = atn(x)
end function

As you can probably guess, the inverse functions for cosecant, secant, and cotangent are arccosecant, arcsecant, and arccotangent.

ASP

function acsc(x)
acsc = asin(1 / x)
end function
function asec(x)
asec = M_PI_2 - acsc(x)
end function
function acot(x)
acot = M_PI_2 - atn(x)
end function

PHP

function acsc($x)
{
return asin(1 / $x);
}
function asec($x)
{
return (M_PI_2 - acsc($x));
}
function acot($x)
{
return (M_PI_2 - atan($x));
}

Next time we'll do something different for a change. I promise.

Trigonometry, Part 2

2008-02-09T08:55:00.000-08:00

As promised, this week we're building some special trigonometry functions using the functions we wrote last week: versed sine (or versine), coversed sine (or coversine), haversed sine (or haversine), hacoversed sine (or hacoversine), exsecant, and excosecant. Actually, to be honest, only two of those build on the functions from last week.

ASP

function versin(x)
versin = 1 - cos(x)
end function
function coversin(x)
coversin = 1 - sin(x)
end function
function haversin(x)
haversin = versin(x) / 2
end function
function hacoversin(x)
hacoversin = coversin(x) / 2
end function
function exsec(x)
exsec = sec(x) - 1
end function
function excsc(x)
excsc = csc(x) - 1
end function

PHP

function versin($x)
{
return (1 - cos($x));
}
function coversin($x)
{
return (1 - sin($x));
}
function haversin($x)
{
return (versin($x) / 2);
}
function hacoversin($x)
{
return (coversin($x) / 2);
}
function exsec($x)
{
return (sec($x) - 1);
}
function excsc($x)
{
return (csc($x) - 1);
}

Next week, the fun continues with inverse trigonometric functions.

Trigonometry, Part 1

2008-02-02T21:33:00.000-08:00

Both ASP and PHP contain three basic trigonometry functions: sin(), cos(), and tan(). You may remember from school that there are three more basic trigonometry functions: cosecant, secant, and cotangent. It might be handy to have some functions for these too.

ASP

function csc(x)
csc = 1 / sin(x)
end function
function sec(x)
sec = 1 / cos(x)
end function
function cot(x)
cot = 1 / tan(x)
end function

PHP

function csc($x)
{
return (1 / sin($x));
}
function sec($x)
{
return (1 / cos($x));
}
function cot($x)
{
return (1 / tan($x));
}

Next week we'll build off some of these basic functions to make some special functions.

A brief introduction

2008-01-29T20:10:00.000-08:00

I thought it would be appropriate in my first post to talk a little bit about myself and why I started this blog. My name is Scott, and I used to be a web developer. I still dabble in code for fun, but professionally I've transitioned to the hardware side of things.

Sad to say, most of my experience has been with ASP, but I am in the process of learning PHP. There are a lot of things in PHP that are missing in ASP, and in some future posts we will bridge this gap a little bit. As I'm learning PHP, there are some things from ASP that I'm finding to be more difficult. Perhaps some reusable code can help to bridge that gap as well.

When I was working on my post-secondary education, the instructors in my programming classes often talked about how we would be writing lots of reusable code over our careers, but they never really offered any practical examples. It took a few years, but eventually I found myself needing to do certain things over and over in different places.

There seems to be a lack of high-quality reusable code available on the Internet, so I thought I would do my part to help change that. My goal is to provide working, practical examples that you can take and use in your own work, even commercially. It's my way of giving back a little bit for all the great blog posts that I learned from.