Question

我是新来的而且我也很喜欢编程我正在尝试创建一个菜单界面，在我输入内容后循环回到开头这是我的代码

#include <stdio.h>
#include <stdlib.h>

int x;
int main()
{MENU:
    printf("Welcome to our menu\n");
    printf("What do you want to do ?\nSelect your option\n\n");
    printf("1. Binary to decimal converter\n");
    printf("2. Lorem ipsum\n");
    printf("3. Lorem ipsum\n");
    printf("4. About us\n");
    printf("5. Quit\n\n");

    printf("Input your option:");
    scanf("%d",&x);
    printf("\n");

    if (x==1){
        printf("This module doesn't exist yet\n\n");

        goto MENU;

    }
    else if (x==2){
        printf("This module doesn't exist yet\n\n");
        goto MENU;
    }
    else if (x==3){
        printf("This module doesn't exist yet\n\n");
        goto MENU;
    }
    else if (x==4){
        printf("About us\n\n");
        printf("Team Members");
        goto MENU;
    }
    else if (x==5){
        printf("Thank you for using this program");
        exit(0);
    }
    else{
        printf("Invalid input");
        goto MENU;
    }


}

现在的问题是，每当我输入1到5之外的其他内容时，整个程序将不停循环。这是为什么？我能做些什么呢？

Answer 1

输入字母字符时，OP会变为无限循环。为了避免这种情况，您可以获取字符串输入（可能是fgets）并检查所有输入字符是否为数字，然后使用atoi等将其转换为int。

Codewise你可以这样做： -

char numbuf[MAX_LEN];
int op,success=0;
while( fgets(numbuf,sizeof numbuf, stdin) ){
   if(sscanf(numbuf, "%d",&op) == 1){
       success=1;
       break;
   }else
     fprintf(stderr,"%s","Error in input, give right one\n");
}
if( success )
// At this point you are sure that you have an int in `op`
success = 0;

完整代码将是这样的： -

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LEN 100
int x;
int main()
{MENU:
    printf("Welcome to our menu\n");
    printf("What do you want to do ?\nSelect your option\n\n");
    printf("1. Binary to decimal converter\n");
    printf("2. Lorem ipsum\n");
    printf("3. Lorem ipsum\n");
    printf("4. About us\n");
    printf("5. Quit\n\n");

    printf("Input your option:");
    char numbuf[MAX_LEN];
    int success = 0;
    while( fgets(numbuf,sizeof numbuf, stdin) ){
       numbuf[strcspn(numbuf, "\n")] = 0;
       if(sscanf(numbuf, "%d",&x) == 1){
         success = 1;
         break;
       }
       else
         fprintf(stderr,"%s","Error in input, give right one\n");
    }
    if( success == 0){
        exit(1);
    }
    success = 0;
    if (x==1){
        printf("This module doesn't exist yet\n\n");

        goto MENU;

    }
    else if (x==2){
        printf("This module doesn't exist yet\n\n");
        goto MENU;
    }
    else if (x==3){
        printf("This module doesn't exist yet\n\n");
        goto MENU;
    }
    else if (x==4){
        printf("About us\n\n");
        printf("Team Members");
        goto MENU;
    }
    else if (x==5){
        printf("Thank you for using this program");
        exit(0);
    }
    else{
        printf("Invalid input");
        goto MENU;
    }


}

我仍然不明白为什么无限循环？

scanf如果匹配格式字符串，则会消耗输入。在这里它没有。所以scanf停止消费它。不匹配的输入仍在输入缓冲区。结果，它被跳过，你得到了提示经常。您也可以通过清除输入缓冲区来消除这种情况。

使用goto并没有错，但它会生成难以维护的代码，而且调试要困难得多。我们可以使用series of if else简单switch-case语句来更清楚地理解。看看这段代码，注意这两件事。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LEN 100

int main()
{
    int x;
    while(1){
        printf("Welcome to our menu\n");
        printf("What do you want to do ?\nSelect your option\n\n");
        printf("1. Binary to decimal converter\n");
        printf("2. Lorem ipsum\n");
        printf("3. Lorem ipsum\n");
        printf("4. About us\n");
        printf("5. Quit\n\n");

        printf("Input your option:");
        char numbuf[MAX_LEN];
        int success = 0;
        while( fgets(numbuf,sizeof numbuf, stdin) ){
           numbuf[strcspn(numbuf, "\n")] = 0;
           if(sscanf(numbuf, "%d",&x) == 1){
             success = 1;
             break;
           }
           else
             fprintf(stderr,"%s","Error in input, give right one\n");
        }
        if( success == 0){
            exit(1);
        }
        success = 0;
        switch(x){
            case 1:
            case 2:
            case 3: printf("This module doesn't exist yet\n\n");
                    continue;
            case 4: printf("About us\n\nTeam Members");
                    continue;
            case 5: printf("Thank you for using this program");
                    exit(0);
            default:printf("Invalid input"); 
        }
    }
    return 0;
}

分开笑话：

Answer 2

你可以通过使用do while循环和切换案例来简化它。

试试这个

int main()
{
int x;
do
{
    printf("Welcome to our menu\n");
    printf("What do you want to do ?\nSelect your option\n\n");
    printf("1. Binary to decimal converter\n");
    printf("2. Lorem ipsum\n");
    printf("3. Lorem ipsum\n");
    printf("4. About us\n");
    printf("5. Quit\n\n");

    printf("Input your option:");
    scanf("%d",&x);
    printf("\n");

    //Switch statement
    switch(x)
    {
    case 1: printf("This module doesn't exist yet\n\n");
            break;
    case 2: printf("This module doesn't exist yet\n\n");
            break;
    case 3: printf("This module doesn't exist yet\n\n");
            break;
    case 4: printf("About us\n\n");
            printf("Team Members");
            break;
    case 5: return 0;
    default: printf("Invalid input");
    }
}while(1);
}

C程序无限循环

2 个答案: