Data type issues

I can't get my head around dealing with all the magic that PHP does to my data. I'm trying to do the following (in C++): char a = 'a'; a = a + 13; The resulting value of a is 'n'. If I do the equivalent in PHP ($a = "a"; $a += 13;) the resulting value is 13. I tried (int)$a += 13;, but that doesn't make a difference. Is there some "whole different way of thinking" I should be engaged in? Is there some way to make PHP add an int to the ASCII value of a single character string (since there seems to be no char type)? Thanks, Peter