Converting letters to other letters

[Anon]

Hi there everyone, I've been working on a encryption program over the past few weeks which does mulitple encryption algorithms to keep a message secure, yet easily decodeable.
What I'm wondering, can someone tell me how I can have a loop which will replace all the letter a's with another variable, probably using a for loop.
What I'm unsure about is how to get it to progress through the alphabet, please help me!

thanks in advance.

[nightowl]

define an array with all the letters

$letterarray = array("a", "b", "c", "d", " A", "B"...)

for ($current_letter = each($letterarray)) {
// your replace code
}

think this should work...