foo.cc: In function 'int main()':
foo.cc:16:30: 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 = 2, k = 0; j < a[i].size(); j++) {
      |                            ~~^~~~~~~~~~~~~
foo.cc:21:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |     for (int j = 2, k = 0; j < b[i].size(); j++) {
      |                            ~~^~~~~~~~~~~~~
foo.cc:35:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   35 |         for (int j = 1, k = 0; j < tem.size(); j++) {
      |                                ~~^~~~~~~~~~~~
foo.cc:38:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |           if (k == a[i].size()-1) {
      |               ~~^~~~~~~~~~~~~~~~
foo.cc:42:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   42 |             for (int z = 1; z < b[i].size(); z++) res += b[i][z];
      |                             ~~^~~~~~~~~~~~~
foo.cc:43:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   43 |             for (int z = j + 1; z < tem.size(); z++) res+=tem[z];
      |                                 ~~^~~~~~~~~~~~
foo.cc:56:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   56 |         for (int j = 1, k = 0; j < tem.size(); j++) {
      |                                ~~^~~~~~~~~~~~
foo.cc:59:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   59 |           if (k == b[i].size()-1) {
      |               ~~^~~~~~~~~~~~~~~~
foo.cc:63:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   63 |             for (int z = 1; z < a[i].size(); z++) res+=a[i][z];
      |                             ~~^~~~~~~~~~~~~
foo.cc:64:35: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   64 |             for (int z = j + 1; z < tem.size(); z++) res += tem[z];
      |                                 ~~^~~~~~~~~~~~

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