程序代码：

#include<stdio.h>
int main()
{
    char day;
    printf("请输入星期首字母：");
    day=getchar();
    switch(day)
    {
    case 'M':printf("Monday\n");break;
    case 'S':printf("输入第二个字母：");scanf("%c",&day);
        if(day=='A') printf("Saturday\n");
        else if(day=='U') printf("Sunday\n");
             else printf("error\n");
        break;
    }
    return 0;
}