/in/foo.cc: In function 'int main()':
/in/foo.cc:13:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<x.size(); ++i) {
               ~^~~~~~~~~
/in/foo.cc:27:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<z.size(); ++i) printf("%c", ans[z[i]-'A'+1]);
               ~^~~~~~~~~