循环中我有问题吗？ [英] I am having problem with do while loop ?

问题描述

当用户给出数值> 0的int值时为什么不执行while循环打印n isforvever，当我在do while循环中删除scanf（）时，它会永久打印n is：？



我尝试过：

when a user give int value of number>0 why doesn't do while loop prints " n is" forvever and when i delete scanf()in do while loop it prints "n is:" forever?

What I have tried:

#include <stdio.h>
#include <stdlib.h>
 int get_negative_int( void);
int main()
{
    int i=get_negative_int();
   printf("%i is negative integer",i);

   }
    int get_negative_int( void){ int n;
       do{
        printf("n is:");
scanf("%i",&n);
       } while (n>0);
       return n;

   }

推荐答案

因为在循环内你改变了n的值：

Because inside the loop you change the value of n:

scanf("%i",&n);

scanf 函数从标准输入流中读取输入 - 通常是用户输入的控制台 - 并将值放入变量中。

因此，当 n 以固定值开始时，每次绕过循环时它会获得一个新值，因此测试时的结尾，而循环每次都会看到不同的值。



这就像一个舞台魔术师做同样的事情反过来的十个成员的卡片技巧：每次他们选择一张卡片，每次都是一张不同的卡片。当其中一个人选择黑桃王牌时，魔术师就停止了这个技巧。

The scanf function reads input from the standard input stream - normally the console, as typed by the user - and puts the value into the variable.
So while n starts as a "fixed value" it gets a new value each time you go round the loop, and so the test at the end of the while loop looks at a different value each time.

It's like a stage magician doing the same card trick on ten members of the audience in turn: each time they get to pick a card, and each time it's a different card. When one of them picks the Ace of Spades, the magician stops doing the trick.

首先，建议：Lear'n缩进你的代码，它有助于阅读。

First, advice: Lear'n to indent your code, it helps reading.

#include <stdio.h>
#include <stdlib.h>
int get_negative_int( void);
int main()
{
	int i=get_negative_int();
	printf("%i is negative integer",i);

}
int get_negative_int( void){
	int n;
	do{
		printf("n is:");
		scanf("%i",&n);
	} while (n>0);
	return n;

}

当你不明白你的代码在做什么或为什么它做它做的事情，答案是调试器。

使用调试器查看代码正在做什么。只需设置断点并查看代码执行情况，调试器允许您逐行执行第1行并在执行时检查变量，这是一个令人难以置信的学习工具。



调试器 - 维基百科，免费的百科全书 [ ^ ]

掌握Visual Studio 2010中的调试 - 初学者指南 [ ^ ]

使用Visual Studio 2010进行基本调试 - YouTube [ ^ ]



调试器在这里向您展示您的代码在做什么你的任务是与它应该做的事情进行比较。

调试器中没有魔法，它没有发现错误，它只是帮助你。当代码没有达到预期的效果时，你就会接近一个错误。

When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute, it is an incredible learning tool.

Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

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