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Lỗi biên dịch:

Main.cc: In function ‘int main()’:
Main.cc:13:5: error: ‘cout’ was not declared in this scope
     cout << "a-b= " << a - b << endl;
     ^~~~
Main.cc:13:5: note: suggested alternative: ‘cosl’
     cout << "a-b= " << a - b << endl;
     ^~~~
     cosl
Main.cc:13:24: error: ‘a’ was not declared in this scope
     cout << "a-b= " << a - b << endl;
                        ^
Main.cc:13:24: note: suggested alternative: ‘ba’
     cout << "a-b= " << a - b << endl;
                        ^
                        ba
Main.cc:13:28: error: ‘b’ was not declared in this scope
     cout << "a-b= " << a - b << endl;
                            ^
Main.cc:13:28: note: suggested alternative: ‘ba’
     cout << "a-b= " << a - b << endl;
                            ^
                            ba
Main.cc:13:33: error: ‘endl’ was not declared in this scope
     cout << "a-b= " << a - b << endl;
                                 ^~~~
Main.cc:13:33: note: suggested alternative: ‘ynl’
     cout << "a-b= " << a - b << endl;
                                 ^~~~
                                 ynl
Main.cc:8:9: warning: unused variable ‘aa’ [-Wunused-variable]
     int aa = 0;
         ^~
Main.cc:9:9: warning: unused variable ‘ab’ [-Wunused-variable]
     int ab = 1;
         ^~
Main.cc:10:9: warning: unused variable ‘bb’ [-Wunused-variable]
     int bb = 0;
         ^~
Main.cc:11:9: warning: unused variable ‘ba’ [-Wunused-variable]
     int ba = -1;
         ^~