C :

#include<stdio.h>
int main()
{
  int a;
  while(scanf("%d",&a)!=EOF)
  {
    if(a>=90)
      printf("A\n");
    else if(a>=80)
      printf("B\n");
    else if(a>=60)
      printf("C\n");
    else
      printf("D\n");
  }
  return 0;
}

C++ :

#include<stdio.h>
int main()
{
	int a;
	while(scanf("%d",&a)!=EOF)
	{
		if(a>=90)
			printf("A\n");
		else if(a>=80)
			printf("B\n");
		else if(a>=60)
			printf("C\n");
		else if(a<60)
			printf("D\n");

	}
	return 0;
}

Java :

import java.util.Scanner;public class Main{public static void main(String[]args){Scanner i=new Scanner(System.in);while(i.hasNext()){int s=i.nextInt();if(s>=90)System.out.println("A");else  if(s>=80)System.out.println("B");else  if(s>=60)System.out.println("C");else  System.out.println("D");}}}