为什么我的代码会崩溃？ [英] Why does my code crash?

问题描述

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

void jum(int *p, int m, int n)
{
    int i;
    if(m==(n-1))
        return;
    if(n%2==0)
    {
        for(i=m;i<n/2;i++)
            (*(p+i))--;
        for(i=n/2;i<n;i++)
            (*(p+i))++;
    }
    else
    {
        for(i=m;i<n/2;i++)
            (*(p+i))--;
        for(i=(n/2)+1;i<n;i++)
            (*(p+i))++;
    }
    jum(p,0,n/2);
    jum(p,n/2,n);
    return;
}

int main()
{
    int n,i;
    printf("n = "); scanf("%d",&n);
    int v[n];
    int *p;
    p=&v[0];
    for(i=0;i<n;i++)
    {
        printf("v[%d] = ",i+1); scanf("%d",&v[i]);
    }
    jum(p,0,n);
    for(i=0;i<n;i++)
        printf("%d ",*(p+i));
    return 0;
}

没有错误/警告，但在我给出矢量值后，它会崩溃。我有一个带有n个元素的向量，然后我想将向量分成两半，左侧将其元素减少1，右侧将其元素添加为1.如果n不均匀，则该元素位于中间会保持不变。将矢量分成两半后，每半部分将再次分割，直到剩下1个元素。



例如：



n = 5;

v = {1,2,3,4,5};

最终打印：0 1 3 5 6



我的尝试：



我不知道该怎么办。我一直在修改代码，直到我到达这个阶段，从我的角度来看，它应该可行。我尝试了一种更简单的代码，使用相同的想法并且它有效，但不能确定为什么它会在这里崩溃。可能是因为我在函数中再次调用该函数。

There is no error/warning, but after I give my vector values, it crashes. I have a vector with n elements and then I wanted to split the vector in half, the left side will have its elements reduced by 1 and the right side will have its elements added by 1. If n is uneven, then the element in the middle will stay the same. After the vector is split in half, every half will be split again until 1 element remains.

For example:

n=5;
v={1 , 2 , 3 , 4 , 5};
Final print: 0 1 3 5 6

What I have tried:

I am not really sure what to try anymore. I kept modifying the code until I reached this stage, which, from my point of view, it should work. I tried a way simpler code with the same idea and it worked but not really sure why it crashes here. Probably because I call the function again in the function.

推荐答案

编译并不意味着你的代码是正确的！ ：笑：

将开发过程想象成编写电子邮件：成功编译意味着您使用正确的语言编写电子邮件 - 例如英语而不是德语 - 而不是电子邮件包含您的邮件想要发送。

所以请停止更改代码并查看会发生什么，并查看运行代码时发生的情况！



现在你进入第二阶段的开发（实际上它是第四或第五阶段的b $ b但是你将在之后的阶段进入）：测试和调试。



首先看看它做了什么，以及它与你想要的有何不同。这很重要，因为它可以为您提供有关其原因的信息。例如，如果程序旨在让用户输入一个数字并将其翻倍并打印答案，那么如果输入/输出是这样的：

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.
So stop just changing the code and seeing what happens, and look at what is happening when you run the code!

And now you enter the second stage of development (in reality it's the fourth or fifth
but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

然后很明显问题出在将它加倍的位 - 它不会将自身加到自身上，或者将它乘以2，它会将它自身相乘并返回输入的平方。

所以，你可以查看代码和很明显，它在某处：

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

private int Double(int value)
   {
   return value * value;
   }

一旦你知道可能出现的问题，就开始使用teh调试器找出原因。在你的线上设一个断点：

Once you have an idea what might be going wrong, start using teh debugger to find out why. Put a breakpoint on your line:

p=&v[0];

并运行你的应用程序。在执行代码之前，请考虑代码中的每一行应该做什么，并将其与使用Step over按钮依次执行每一行时实际执行的操作进行比较。它符合您的期望吗？如果是这样，请转到下一行。

如果没有，为什么不呢？它有何不同？



这是一项非常值得开发的技能，因为它可以帮助你在现实世界和发展中。和所有技能一样，它只能通过使用来改善！



是的，我可能会告诉你问题是什么 - 但这并不难做到，你会在同一时间学到一些非常值得的东西！

and run your app. Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?

This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Yes, I could probably tell you what "the problem" is - but it's not difficult to do this yourself, and you will learn something really worthwhile at the same time!

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