---

Lỗi biên dịch:

Main.cc: In function ‘int main()’:
Main.cc:9:12: error: ‘A’ was not declared in this scope
     cin << A << B << X << Y;
            ^
Main.cc:9:17: error: ‘B’ was not declared in this scope
     cin << A << B << X << Y;
                 ^
Main.cc:9:22: error: ‘X’ was not declared in this scope
     cin << A << B << X << Y;
                      ^
Main.cc:9:27: error: ‘Y’ was not declared in this scope
     cin << A << B << X << Y;
                           ^