foo.cc: In function 'void mul(int, int)':
foo.cc:22:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |                 for (int j = 0;j < ans.size();j++)//执行乘法运算
      |                                ~~^~~~~~~~~~~~
foo.cc:29:42: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   29 |                         for (int j = 0;j < ans.size();j++)
      |                                        ~~^~~~~~~~~~~~
foo.cc:36:51: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   36 |                                         if (j + 1 > ans.size() - 1)//判断是否超出范围
      |                                             ~~~~~~^~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务