/in/foo.cc: In function 'std::vector<int> mul(std::vector<int>&, int)':
/in/foo.cc:19:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for( int i = 0; i < A.size() || t; i++ ){
                     ~~^~~~~~~~~~
/in/foo.cc:20:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if( i < A.size() ) t = A[i] * b + t; // 大整数每位与乘数相乘，再加上进位
             ~~^~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:67:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<ans.size();i++)cout<<ans[i];
                 ~^~~~~~~~~~~