If the current character of the first string is not an alphanumeric character , increase the pointer i
while ( i < len1 && ( ! ( ( str1 [ i ] >= ' a ' && str1 [ i ] <= ' z ' ) || ( str1 [ i ] >= ' A ' && str1 [ i ] <= ' Z ' ) || ( str1 [ i ] >= '0' && str1 [ i ] <= '9' ) ) ) ) { i ++ ; }