/in/foo.cc: In function 'bool checkValid(int, int)':
/in/foo.cc:8:9: warning: statement has no effect [-Wunused-value]
   for (i; i <= j; ++i) {
         ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:20:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < src.length(); ++i) {
                   ~~^~~~~~~~~~~~~~