---

Lỗi biên dịch:

Main.cc: In function ‘int main()’:
Main.cc:9:8: error: ‘cin’ was not declared in this scope
        cin >> a >> b >> x >> y;
        ^~~
Main.cc:9:8: note: suggested alternative: ‘sin’
        cin >> a >> b >> x >> y;
        ^~~
        sin
Main.cc:10:8: error: ‘cout’ was not declared in this scope
        cout << a*x+b*y;
        ^~~~
Main.cc:10:8: note: suggested alternative: ‘cosl’
        cout << a*x+b*y;
        ^~~~
        cosl