求解，怎么写这道C语言

char fun(int score)
{
	switch (score / 10)
	{
	case10:
	case 9:
		return 'A';
	case 8:
		return 'B';
	case 7:
	case 6:
		return 'C';
	default:
		return 'D';
	}
}

#include <stdio.h>

char fun (int score)
{
   switch (score >= 90)
   {
   case 1:
       return 'A';
       break;
   case 0:
       switch (score >= 80)
       {
       case 1:
           return 'B';
           break;
       case 0:
           switch (score >= 60)
           {
           case 1:
               return 'C';
               break;
           case 0:
               return 'D';
               break;
           }
           break;
       }
       break;
   }
}

void main()
{
    int score;
    char p;
    scanf("%d", &score);
    p=fun(score);
    printf("%c\n", p);
}