foo.cc: In function 'std::vector<int> subct(std::vector<int>&, std::vector<int>&)':
foo.cc:24:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |     for(int i = 0; i < A.size(); i++){ //从低位开始相减
      |                    ~~^~~~~~~~~~
foo.cc:26:10: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   26 |      if(i<B.size()) t-=B[i];
      |         ~^~~~~~~~~

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