这要怎么做啊 哪位能帮帮我

int main()
{
    double num;
    scanf("%lf",&num);
    
    switch((int)num)
    {
        case 90 ... 100:
            printf("优\n");
            break;
        case 80 ... 89:
            printf("良\n");
            break;
        case 70 ... 79:
            printf("中\n");
            break;
    }
    
    return 0;
}

记得采纳哦，谢谢