/in/foo.cc: In function 'int main()':
/in/foo.cc:11:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < s1.length(); ++i) {
                    ^
/in/foo.cc:12:13: warning: array subscript has type 'char' [-Wchar-subscripts]
    sum[s1[i]][0]++;
             ^
/in/foo.cc:14:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < s2.length(); ++i) {
                    ^
/in/foo.cc:15:13: warning: array subscript has type 'char' [-Wchar-subscripts]
    sum[s2[i]][1]++;
             ^