c 语言 限制用户的选项（菜单浏览）

1、

#include <stdio.h>

int main(void)
{
    char choice;
    
    printf("a) xxxx    b) yyyy
");
    printf("c) zzzz    q) quit.
");
    printf("input your choice: ");
    
    while((choice = getchar()) != 'q')
    {
        switch(choice)
        {
            case 'a': printf("choose a.
"); break;
            case 'b': printf("choose b.
"); break;
            case 'c': printf("choose c.
"); break;
            default: printf("input errer, the range is a b c q
"); break;    
        }
        while(getchar() != '
')
            continue;
        printf("

a) xxxx    b) yyyy
");
        printf("c) zzzz    q) quit.
");
        printf("input your choice: ");
    }    
    
    return 0;
} 

2、

#include <stdio.h>

char get_choice(void);

int main(void)
{
    char choice;
    while((choice = get_choice()) != 'q')
    {
        switch(choice)
        {
            case 'a': printf("you choose a.

"); break;
            case 'b': printf("you choose b.

"); break;
            case 'c': printf("you choose c.

"); break;
            default: printf("grogramm ereor.

"); break;    
        }    
    }    
    
    return 0;
} 

char get_choice(void)
{
    char ch;
    printf("a) xxx    b) yyyy
");
    printf("c) zzz    q) quit
");
    printf("your choice: ");
    
    ch = getchar();
    while(getchar() != '
')
        continue;
    while(ch < 'a' || ch > 'c' && ch != 'q')
    {
        printf("the range is a b c and q, try again: ");
        ch = getchar();
        while(getchar() != '
')
            continue;
    }

    return ch;
}

3、

#include <stdio.h>

char get_choice(void);

int main(void)
{
    char choice;
    while((choice = get_choice()) != 'q')
    {
        switch(choice)
        {
            case 'a': printf("you choose a.

"); break;
            case 'b': printf("you choose b.

"); break;
            case 'c': printf("you choose c.

"); break;
            default: printf("grogramm ereor.

"); break;    
        }    
    }    
    
    return 0;
} 

char first_choice(void);
char get_choice(void)
{
    char ch;
    printf("a) xxx    b) yyyy
");
    printf("c) zzz    q) quit
");
    printf("your choice: ");
    
    ch = first_choice();

    while(ch < 'a' || ch > 'c' && ch != 'q')
    {
        printf("the range is a b c and q, try again: ");
        ch = first_choice();

    }

    return ch;
}

char first_choice(void)
{
    char ch;
    
    ch = getchar();
    while(getchar() != '
')
        continue;
    
    return ch;
}