程序代码：

#include "stdio.h"
main()
{
    int x;
    scanf("%d",&x);
    switch(x)
    {case 0<=x&&x<=59:printf("不及格\n");break;
    case 60<=x&&x<=79:printf("及格\n");break;
    case 80<=x&&<=100:printf("优秀");break;
    default:printf("请输出成绩0-100");}
}