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:9:17: error: ‘swap’ was not declared in this scope
    9 |                 swap(a,b);
      |                 ^~~~
foo.cc:11:17: error: ‘swap’ was not declared in this scope
   11 |                 swap(b,c);
      |                 ^~~~
foo.cc:13:17: error: ‘swap’ was not declared in this scope
   13 |                 swap(a,c);
      |                 ^~~~
foo.cc:15:9: error: ‘cout’ was not declared in this scope
   15 |         cout<<a<<""<<b<<""<<c<<endl;
      |         ^~~~
foo.cc:15:32: error: ‘endl’ was not declared in this scope
   15 |         cout<<a<<""<<b<<""<<c<<endl;
      |                                ^~~~
foo.cc:17:17: error: expected ‘;’ before ‘}’ token
   17 |         return 0
      |                 ^
      |                 ;
   18 | }
      | ~