/in/foo.cc: In function 'int main()':
/in/foo.cc:7:5: error: 'cout' is not a member of 'std'
     std::cout << "请输入第一个数: ";
     ^~~
/in/foo.cc:8:5: error: 'cin' is not a member of 'std'
     std::cin >> num1;
     ^~~
/in/foo.cc:10:5: error: 'cout' is not a member of 'std'
     std::cout << "请输入第二个数: ";
     ^~~
/in/foo.cc:11:5: error: 'cin' is not a member of 'std'
     std::cin >> num2;
     ^~~
/in/foo.cc:13:5: error: 'cout' is not a member of 'std'
     std::cout << "请输入第三个数: ";
     ^~~
/in/foo.cc:14:5: error: 'cin' is not a member of 'std'
     std::cin >> num3;
     ^~~
/in/foo.cc:33:5: error: 'cout' is not a member of 'std'
     std::cout << num1 << num2 << num3 << std::endl;
     ^~~
/in/foo.cc:33:42: error: 'endl' is not a member of 'std'
     std::cout << num1 << num2 << num3 << std::endl;
                                          ^~~