Language: C

int main(void)
{
	float a, b;
	
	while (scanf("%f %f", &a, &b) != EOF){
	
		if ( a < 35.5 && b < 71){
			printf("AAA\n");
		}
		else if ( a < 37.5 && b < 77){
			printf("AA\n");
		}
		else if ( a < 40 && b < 83){
			printf("A\n");
		}
		else if ( a < 43 && b < 89){
			printf("B\n");
		}
		else if ( a < 50 && b < 105){
			printf("C\n");
		}
		else if ( a < 55 && b < 114){
			printf("D\n");
		}
		else if ( a < 70 && b < 148){
			printf("E\n");
		}
		else {
			printf("NA\n");
		}
	}
	
	return (0);
}

Compiler output:
main.c: In function 'main':
main.c:5:16: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    5 |         while (scanf("%f %f", &a, &b) != EOF){
      |                ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | int main(void)
main.c:5:16: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    5 |         while (scanf("%f %f", &a, &b) != EOF){
      |                ^~~~~
main.c:5:16: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:5:42: error: 'EOF' undeclared (first use in this function)
    5 |         while (scanf("%f %f", &a, &b) != EOF){
      |                                          ^~~
main.c:5:42: note: 'EOF' is defined in header '<stdio.h>'; this is probably fixable by adding '#include <stdio.h>'
main.c:5:42: note: each undeclared identifier is reported only once for each function it appears in
main.c:8:25: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    8 |                         printf("AAA\n");
      |                         ^~~~~~
main.c:8:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:8:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:8:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:11:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   11 |                         printf("AA\n");
      |                         ^~~~~~
main.c:11:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:14:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   14 |                         printf("A\n");
      |                         ^~~~~~
main.c:14:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:17:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   17 |                         printf("B\n");
      |                         ^~~~~~
main.c:17:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:20:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   20 |                         printf("C\n");
      |                         ^~~~~~
main.c:20:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:23:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   23 |                         printf("D\n");
      |                         ^~~~~~
main.c:23:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:26:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   26 |                         printf("E\n");
      |                         ^~~~~~
main.c:26:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:29:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   29 |                         printf("NA\n");
      |                         ^~~~~~
main.c:29:25: note: include '<stdio.h>' or provide a declaration of 'printf'