/in/foo.cc: In function 'int main()':
/in/foo.cc:14:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0;j<s.size();j++)
                ^
/in/foo.cc:17:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int k=j;k<s.size();k++)
                 ^