order n^2 is slow

-1 [optimization] redundent test for end of string
-1 [optimization] return staement has useless extra expression
-1 [security, buff overflowlike] no range check if string does not contain alpha
-? does char cache[26] ={0}; zero all elements when var is type auto
(stack storage)
-1 [warning] (tolower(str[i]-'a') is of type int assigned to smaller type char
-1 [c99] decl var i in loop is only c99 and later