Language: C++

#include <iostream>
using namespace
int main()
{
	int H, W, i, j;
	while(1){
		cin >> H >> W;
		if(W == 0 & H == 0)
			break;
		
		for( i = 0; i < H; i++){
			for( j = 0; j < H; j++){
				if((i + j) % 2 == 0){
					cout << "#";
				}else{
					cout << ".";
				}
				cout << endl;
			}
			cout << endl;
		}
	}
	return 0;
}

Compiler output:
a.cc:3:1: error: expected identifier before 'int'
    3 | int main()
      | ^~~
a.cc:2:16: error: expected ';' before 'int'
    2 | using namespace
      |                ^
      |                ;
    3 | int main()
      | ~~~             
a.cc: In function 'int main()':
a.cc:7:17: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |                 cin >> H >> W;
      |                 ^~~
      |                 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:14:41: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   14 |                                         cout << "#";
      |                                         ^~~~
      |                                         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:16:41: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   16 |                                         cout << ".";
      |                                         ^~~~
      |                                         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:18:33: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   18 |                                 cout << 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:18:41: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   18 |                                 cout << 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:20:25: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   20 |                         cout << 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:20:33: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   20 |                         cout << endl;
      |                                 ^~~~
      |                                 std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~