Language: C

int main(void){
	int a = 0;
	int b = 0;
	int i = 0;
	int j = 0;

	while (1){
		scanf("%d %d", &a, &b);
		if (a == 0 && b == 0){
			break;
		}
		for (i = 0; i < a; i++){
			if (a % 2 == 1){
				for (j = 0; j < b; j++){
					if (j % 2 == 1){
						printf("%c", '#');
					}
					else{
						printf("%c", '.');
					}
				}
				printf("\n");
			}else if (a % 2 == 0){
				for (j = 0; j < b; j++){
					if (j % 2 == 1){
						printf("%c", '.');
					}else{
						printf("%c", '#');
					}
				}
				printf("\n");
			}
		printf("\n");
		}
	return 0;
}

Compiler output:
main.c: In function 'main':
main.c:8:17: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    8 |                 scanf("%d %d", &a, &b);
      |                 ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | int main(void){
main.c:8:17: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    8 |                 scanf("%d %d", &a, &b);
      |                 ^~~~~
main.c:8:17: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:16:49: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   16 |                                                 printf("%c", '#');
      |                                                 ^~~~~~
main.c:16:49: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:16:49: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:16:49: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:19:49: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   19 |                                                 printf("%c", '.');
      |                                                 ^~~~~~
main.c:19:49: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:22:33: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   22 |                                 printf("\n");
      |                                 ^~~~~~
main.c:22:33: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:26:49: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   26 |                                                 printf("%c", '.');
      |                                                 ^~~~~~
main.c:26:49: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:28:49: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   28 |                                                 printf("%c", '#');
      |                                                 ^~~~~~
main.c:28:49: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:31:33: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   31 |                                 printf("\n");
      |                                 ^~~~~~
main.c:31:33: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:33:17: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   33 |                 printf("\n");
      |                 ^~~~~~
main.c:33:17: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:36:1: error: expected declaration or statement at end of input
   36 | }
      | ^