C - 棘手的开关盒工作..！ [英] C - Tricky Switch Case working .. !

问题描述

各位，

最近开始学习 C.
卡在一个点上.它是关于 switch-case 语句的工作.

Recently started learning C.
Stuck at a point. Its about working of switch-case statement.

代码如下:

#include<stdio.h>

int main() {
        int i=4;
        switch(i) {

                default :       
                        printf("%s","Default");
                case 0:         
                        printf("%s","Case 0");
                case 1:         
                        printf("%s","Case 1");
                case 2:         
                        printf("%s","Case 2");

        return 0;
        }
 }  

我个人认为，应该打印Default"，因为它与任何大小写值都不匹配.
但是当我在 Turbo C 中运行代码时，我观察到的是:

I personally think, "Default" should be printed, as it doesn't match with any of case value.
But when I run the code in Turbo C, what I observed was this :

Default
Case 0
Case 1
Case 2  

这里也观察到了同样的情况:http://www.ideone.com/pFh1d

Even same was observed here : http://www.ideone.com/pFh1d

有什么问题?这是编译器问题还是我的代码中的任何错误?

What is the problem ? It is the compiler problem or any mistake in my code ?

PS:如果我必须首先编写默认情况，这有什么错.有什么危害吗?

但是一旦编译器知道它必须执行default语句，为什么还要在default case语句之后放一个break语句呢?

推荐答案

switch 语句将跳转到相应的 case 或 default 然后代码将继续直到下一个 break 语句.

The switch statement will jump to the appropriate case or default and then the code will continue until the next break statement.

由于您的代码没有 break，它将从 default: 开始，然后继续执行以下所有语句.在编写类似条件时，这有时是一个有用的技巧，但通常缺少 break 语句会导致混淆.

As your code has no break it will start off at the default: and simply continue through all the following statements. This can sometimes be a useful trick when programming similar conditions, but generally the lack of break statements will cause confusion.

还有最后的 return 在 switch 语句之后的错误位置.

Also the final return is in the wrong place it should be after the switch statement.

修改如下.

        int i=4;
        switch(i) {

                default :       
                        printf("%s","Default");
                        break;
                case 0:         
                        printf("%s","Case 0");
                        break;
                case 1:         
                        printf("%s","Case 1");
                        break;
                case 2:         
                        printf("%s","Case 2");
                        break;

        }
        return 0;

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