foo.cc: In function 'void colsort(std::vector<std::vector<int> >&)':
foo.cc:11:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |  for (int i = 0; i < M[0].size(); i++) {
      |                  ~~^~~~~~~~~~~~~
foo.cc:12:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |   for (int j = 0; j < M.size(); j++) {
      |                   ~~^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:37:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   37 |  for (int i = 0; i < M.size(); i++) {
      |                  ~~^~~~~~~~~~
foo.cc:38:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |   for (int j = 0; j < M[i].size(); j++) {
      |                   ~~^~~~~~~~~~~~~
foo.cc:40:10: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   40 |    if (i != M.size() - 1) {
      |        ~~^~~~~~~~~~~~~~~

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