Edit: I just noticed, the author of the original writeup said "for for loops" instead of "for loops". I'll leave this writeup standing though if nobody minds, since it is a pretty good description of simple mIRC looping. Actually, mIRC has support for looping, you can use goto loops and while loops.

Example:

(goto loop)
alias onetoten {
var %x = 0
:loop
inc %x
echo -a %x
if (%x < 10) goto loop
}

(while loop)
alias onetoten {
var %x = 0
while (%x < 10) {
inc %x
echo -a %x
}
}

Both are perfectly valid loops, I heard that while loops execute faster than goto loops but I'm not sure if it's true.