/in/foo.cc: In function 'int main()':
/in/foo.cc:12:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < s.length(); i++){
                    ~~^~~~~~~~~~~~
/in/foo.cc:9:14: warning: unused variable 'last' [-Wunused-variable]
     int num, last, c1, c2;
              ^~~~