C ++递归函数，用于打印不起作用的标尺. [英] C++ Recursive function for printing a ruler not working.

问题描述

我一直试图从一本书中教自己C ++.以下代码是一个问题，因为我无法弄清楚自己在做什么.代码是本书中的一个示例，但不会带来相同的结果.

I've been trying to teach myself C++ from a book. The following piece of code has been a problem, as I can't figure out what I'm doing wrong.The code is an example from the book, and yet it won't bring the same result.

函数subdivide()应该使用分而治之的方法来在中点分割数组并打印字符'|'.在那里(给人一种尺子的错觉)，随后在每条新行上进行中点打印.问题是，最终的印刷品仅包含字符"|"在所有行的端点，中间没有字符.

The function subdivide() is supposed to use the divide and conquer method for dividing the array at midpoint and printing the character '|' there(creating an illusion of a ruler), with subsequent mid-point printing at every new line. The problem is, the final print contains only the character '|' at the end-points in all the lines, and no character is printed in the middle.

我试图发布图片，但是显然我不能.

I tried to post an image, but apparently I can't.

我将不胜感激.这是C ++代码:

I'll appreciate any help. Here's the C++ code:

//using recursion to subdivide a ruler
#include<iostream>
const int len=66;
const int div=6;
void subdivide(char ar[], int min,int max,int level);

int main()
{
using namespace std;
    char ruler[len];
    int i;
    for(int i=1; i<(len-2); i++)
        ruler[i]=' ';
    ruler[len-1]='\0';

    int min=0;
    int max=len-2;
    ruler[min]=ruler[max]='|';

    cout<<ruler<<endl;

    for(i=1;i<=div;i++){
        subdivide(ruler, min, max, i);
        cout<<ruler<<endl;
          for(int j=1; j<len-2; j++)
                ruler[j]=' ';
    }

return 0;
}

void subdivide(char ar[],int low,int high,int level)
{
using namespace std;
if (level==0);
    return;
int mid=(high+low)/2;
ar[mid]='|';
subdivide(ar, low, mid, level-1);
subdivide(ar, mid, high, level-1);
}

推荐答案

在您的 subdivide 函数中，if后面有分号:

In your subdivide function, you have a semicolon after the if:

if (level==0);
    return;

缩进是在欺骗，而您的代码实际在做什么

The indentation is deceiving, and what your code is actually doing is

if (level==0);  //does nothing
return; // always returns (before modifying the ruler)

将其更改为

if (level==0)    //no semicolon here
    return;

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