---

Lỗi biên dịch:

Main.cc: In function ‘int main()’:
Main.cc:8:21: error: ‘cin’ was not declared in this scope
     int a, b, x, y; cin >> a >> b >> x >> y;
                     ^~~
Main.cc:8:21: note: suggested alternative: ‘sin’
     int a, b, x, y; cin >> a >> b >> x >> y;
                     ^~~
                     sin
Main.cc:9:5: error: ‘cout’ was not declared in this scope
     cout << a * x + b * y;
     ^~~~
Main.cc:9:5: note: suggested alternative: ‘cosl’
     cout << a * x + b * y;
     ^~~~
     cosl