C :

#include<stdio.h>
int main()
{
    int x;
    char grade;
    scanf("%d",&x);
    if(x>=90)   grade='A';
    else if(x>79) grade='B';
    else if(x>69) grade='C';
    else if(x>59) grade='D';
    else grade='E';
    printf("%c\n",grade);
    return 0;
}

C++ :

#include<iostream>
using namespace std;
int main()
{
  int a;
  cin>>a;
  if(a>=0&&a<=100)
  {
    if(a>=90)
   cout<<'A'<<endl;
    else if(a>=80)
      cout<<'B'<<endl;
      else if(a>=70)
     cout<<'C'<<endl;
      else if(a>=60)
     cout<<'D'<<endl;
      else
      cout<<'E'<<endl;
      }
 return 0; 
}