/in/foo.cc: In function 'int main()':
/in/foo.cc:21:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0;i <strlen(h1) ;i++) {
                 ~~^~~~~~~~~~~
/in/foo.cc:22:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0;j < strlen(h2);j++) {
                  ~~^~~~~~~~~~~~
/in/foo.cc:26:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0;i < strlen(h1) + strlen(h2);i++) {
                 ~~^~~~~~~~~~~~~~~~~~~~~~~~~