Language: C++

#include <iostream>
using namespace cout << std;

int main(){

	int a,b;
	cin >> a >> b;
	if( a < b ){
		cout << "a < b" << endl;
    }
    else if ( a > b ){
    	cout << "a > b"  << endl;
    }
    else if ( a == b ){
    	cout << "a == b" << endl;
    }
}

Compiler output:
a.cc:2:17: error: 'cout' is not a namespace-name
    2 | using namespace cout << std;
      |                 ^~~~
a.cc:2:21: error: expected ';' before '<<' token
    2 | using namespace cout << std;
      |                     ^~~
      |                     ;
a.cc:2:22: error: expected unqualified-id before '<<' token
    2 | using namespace cout << std;
      |                      ^~
a.cc: In function 'int main()':
a.cc:7:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |         cin >> a >> b;
      |         ^~~
      |         std::cin
In file included from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:9:17: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    9 |                 cout << "a < b" << endl;
      |                 ^~~~
      |                 std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:9:36: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    9 |                 cout << "a < b" << endl;
      |                                    ^~~~
      |                                    std::endl
In file included from /usr/include/c++/14/iostream:41:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:12:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   12 |         cout << "a > b"  << endl;
      |         ^~~~
      |         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:12:29: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   12 |         cout << "a > b"  << endl;
      |                             ^~~~
      |                             std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:15:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   15 |         cout << "a == b" << endl;
      |         ^~~~
      |         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:15:29: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   15 |         cout << "a == b" << endl;
      |                             ^~~~
      |                             std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~