If the current character of the second string is not an alphanumeric character , increase the pointer j
while ( j < len2 && ( ! ( ( str2 [ j ] >= ' a ' && str2 [ j ] <= ' z ' ) || ( str2 [ j ] >= ' A ' && str2 [ j ] <= ' Z ' ) || ( str2 [ j ] >= '0' && str2 [ j ] <= '9' ) ) ) ) { j ++ ; }