程序代码：

#include <stdio.h>
void judgeT();
void judgeS();
int main()
{
   char I;//用I来存储星期首字母
   while (~scanf("%c",&I))
   {
      switch(I)
        {
            case 'M':printf("星期一\n");break;
            case 'W':printf("星期三\n");break;
            case 'F':printf("星期五\n");break;
            case 'T':judgeT();break;
            case 'S':judgeS();break;
            default:printf("wrong letter!\n");
        }
   }
    return 0;
}
void judgeT()//通过输入第二字字母来进一步判断星期几
{
    char a;
    printf("Please input the second letter:");
    scanf("%c",&a);
    if(a=='u')printf("星期二\n");
    if(a=='h')printf("星期四\n");
}
void judgeS()//通过输入第二字字母来进一步判断星期几
{
    char a;
    printf("Please input the second letter:");
    scanf("%c",&a);
    if(a=='a')printf("星期六\n");
    if(a=='u')printf("星期天\n");
}

程序代码：

#include <stdio.h>

void judgeT();
void judgeS();

int main(void) {
    char input;
    int flag = 1;

    while(flag) {
        scanf("%c", &input);
        fflush(stdin);

        switch(input) {
            case 'm':
            case 'M':
                printf("星期一\n");
                break;

            case 'w':
            case 'W':
                printf("星期三\n");
                break;

            case 'f':
            case 'F':
                printf("星期五\n");
                break;

            case 't':
            case 'T':
                judgeT();
                break;

            case 's':
            case 'S':
                judgeS();
                break;

            case 'q':
            case 'Q': 
                flag = 0;
                break;

            default:
                printf("wrong letter!\n");
                break;
        }
    }

    return 0;
}

void judgeT() {
    char a;
    printf("Please input the second letter:\n");
    scanf("%c", &a);

    if(a == 'u' || a == 'U') printf("星期二\n");

    if(a == 'h' || a == 'H') printf("星期四\n");
}

void judgeS() {
    char a;
    printf("Please input the second letter:\n");
    scanf("%c", &a);
    fflush(stdin);

    if(a == 'a' || a == 'A') printf("星期六\n");

    if(a == 'u' || a == 'U') printf("星期天\n");
}