XML Sitemap Date Format In PHP

The Luhn algorithm was created by Hans Peter Luhn and is a way of creating a simple checksum for a number. This algorithm, also known as the mod 10 algorithm, is used in a wide variety of applications but is commonly associated with credit card numbers.

If you look at the numbers on the front of your credit card the last digit on the right is the checksum. An algorithm is done on the other numbers and if the checksum is the same then the number is considered valid.

As another step up from the game of snake I created in my last post I decided to try my hand at creating a side scrolling shooter. Just like my other posts, this is an ASCII based game played on the command line.

A side scrolling shooter, if you didn't already know, moves a scene from right to left across the screen with enemies moving with the scene towards the player's ship, which is on the left hand side of the scene. The player can fire bullets towards the enemies so remove them from the scene.

Computers are not that great at creating random numbers as the methods they use are deterministic. That is, they start from a number (called a seed) and apply maths to that number to generate pseudorandom numbers. Most random numbers generated by computers programs use a seed provided by the system, which is generally the current time. If you can guess the initial value then you can start to work out what the random sequence of numbers generated is. Most random numbers, are therefore not suitable for encryption.

I was looking for a function that searched an array for another array, and after not finding one I decided to write it. What I was looking for was a function that took a smaller array and searched for that exact sequence of items in a larger array. As it happens, PHP does have a number of array search functions, but they didn't produce the correct result.

When creating regular expressions for PHP I tend to use the awesome tool PHP Live Regex.

This tool has really helped me over the last couple of years to create regular expressions for many of the projects I've been working on. Everything from validation functions to formatters that use regular expressions have had their expressions worked out using this tool. I even use it for testing one off expressions where I just need to find/replace in a file.