foo.cc: In function ‘int main()’:
foo.cc:6:9: error: ‘cin’ was not declared in this scope
    6 |         cin>>a>>b>>c;
      |         ^~~
foo.cc:13:9: error: ‘cout’ was not declared in this scope
   13 |         cout<<b<<a<<endl;
      |         ^~~~
foo.cc:13:21: error: ‘endl’ was not declared in this scope
   13 |         cout<<b<<a<<endl;
      |                     ^~~~