Mã chấm: 13669

Main.cc: In function ‘int main()’:
Main.cc:7:10: error: ‘a’ was not declared in this scope
     cin>>a>>b>>c>>x;
          ^
Main.cc:7:13: error: ‘b’ was not declared in this scope
     cin>>a>>b>>c>>x;
             ^
Main.cc:7:16: error: ‘c’ was not declared in this scope
     cin>>a>>b>>c>>x;
                ^
Main.cc:7:19: error: ‘x’ was not declared in this scope
     cin>>a>>b>>c>>x;
                   ^