compare datat string char by char then.....do somthing

[gmabcc5]

i have a set of data string that i want to compare character by character to find out how they differ. if they are different find the positions in which it changed. the changed happened at position 1 then do something if the changed happened at position 13 then do something.

ex.
10200K00S
1020KK00S 'changed happened at 5th position
1020KK000 ' changed happened at 9th position