C :

#include<stdio.h>
main()
{
	int score;
	scanf("%d",&score);
	if(score>=90)
		printf("%d-A\n",score);
	else if(score>=80)
		printf("%d-B\n",score);
	else if(score>=70)
		printf("%d-C\n",score);
	else if(score>=60)
		printf("%d-D\n",score);
	else
		printf("%d-E\n",score);
}

C++ :

#include<bits/stdc++.h>
using namespace std;
int d;
int main()
{
	cin>>d;
	switch(d)
	{
		case 90 ...100:cout<<d<<"-A";break;
		case 80 ...89:cout<<d<<"-B";break;
		case 70 ...79:cout<<d<<"-C";break;
		case 60 ...69:cout<<d<<"-D";break;
		default:cout<<d<<"-E";
	}
   return 0;
}