/in/foo.cc: In function 'int main()':
/in/foo.cc:15:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   15 |         for(int i = 1; i <= s2.length(); i++)
      |                        ~~^~~~~~~~~~~~~~
/in/foo.cc:16:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   16 |                 for(int j = 1; j <= s1.length(); j++) c[i + j - 1] += a[j] * b[i];
      |                                ~~^~~~~~~~~~~~~~
/in/foo.cc:17:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |         for(int i = 1; i < s1.length() + s2.length(); i++)
      |                        ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
/in/foo.cc:14:13: warning: unused variable 't' [-Wunused-variable]
   14 |         int t = 0;
      |             ^