foo.cc: In function 'bool cmp(std::string, std::string)':
foo.cc:11:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |     for (int i = 0; i < a.size(); i ++ )
      |                     ~~^~~~~~~~~~
foo.cc: In function 'std::string add(std::string, std::string)':
foo.cc:31:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   31 |     for (int i = 0; i < A.size(); i ++ )
      |                     ~~^~~~~~~~~~
foo.cc:34:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   34 |         if (i < B.size()) t += B[i];
      |             ~~^~~~~~~~~~
foo.cc: In function 'std::string sub(std::string, std::string)':
foo.cc:56:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   56 |     for (int i = 0, t = 0; i < A.size(); i ++ )
      |                            ~~^~~~~~~~~~
foo.cc:59:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   59 |         if (i < B.size()) t -= B[i];
      |             ~~^~~~~~~~~~
foo.cc: In function 'std::string mul(std::string, std::string)':
foo.cc:83:51: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |         for (int j = 0; j <= i; j ++ ) C[i] += (j < a.size() ? A[j] : 0) * ((i - j) < b.size() ? B[i - j] : 0);
      |                                                 ~~^~~~~~~~~~
foo.cc:83:85: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |         for (int j = 0; j <= i; j ++ ) C[i] += (j < a.size() ? A[j] : 0) * ((i - j) < b.size() ? B[i - j] : 0);
      |                                                                             ~~~~~~~~^~~~~~~~~~
foo.cc: In function 'std::string mul(std::string, int)':
foo.cc:107:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  107 |     for(int i = 0; i < A.size() || t; i ++ )
      |                    ~~^~~~~~~~~~
foo.cc:109:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  109 |         if(i < A.size()) t += A[i] * b;
      |            ~~^~~~~~~~~~

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