Help converting letters to number

I was woundering how i would set this up: I a a varibale that has letters and numbers, the lenght of the variable can change. I was wanting to convert the letters to a number so it is all numbers. I'm pretty sure ill have to make it a string but then im kinda lost.

$var='A7601000aFBFBEFB33528985'
LettersToNumbers()
;===============================================================================
Func LettersToNumbers()
If $var = 'A' Then $var = 1
If $var = 'B' Then $var = 2
If $var = 'C' Then $var = 3
If $var = 'D' Then $var = 4
If $var = 'E' Then $var = 5
If $var = 'F' Then $var = 6
If $var = 'G' Then $var = 7
If $var = 'H' Then $var = 8
If $var = 'I' Then $var = 9
If $var = 'J' Then $var = 10
If $var = 'K' Then $var = 11
If $var = 'L' Then $var = 12
If $var = 'M' Then $var = 13
If $var = 'N' Then $var = 14
If $var = 'O' Then $var = 15
If $var = 'P' Then $var = 16
If $var = 'Q' Then $var = 17
If $var = 'R' Then $var = 18
If $var = 'S' Then $var = 19
If $var = 'T' Then $var = 20
If $var = 'U' Then $var = 21
If $var = 'V' Then $var = 22
If $var = 'W' Then $var = 23
If $var = 'X' Then $var = 24
If $var = 'Y' Then $var = 25
If $var = 'Z' Then $var = 26
MsgBox  (0,'',$var)
EndFunc
;===============================================================================