/in/foo.cc: In function 'int main()':
/in/foo.cc:23:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0;i < s1.length();i++)
                          ^
/in/foo.cc:12:9: warning: unused variable 'm' [-Wunused-variable]
     int m = 0;
         ^