Reverse array with recursion in C programming

Question

I was having some problem when trying to do a reverse array using recursion. Here is the function prototype:

void rReverseAr(int ar[ ], int size);

And here is my code:

int main()
{
    int ar[10], size, i;

    printf("Enter array size: ");
    scanf("%d", &size);
    printf("Enter %d numbers: ", size);
    for (i = 0; i<size; i++)
        scanf("%d", &ar[i]);
    rReverseAr(ar, size);
    printf("rReverseAr(): ");
    for (i = 0; i<size; i++)
        printf("%d ", ar[i]);
    return 0;
}

void rReverseAr(int ar[], int size) {
    int start = 0, end = size - 1, temp;
    if (start < end) {
        temp = ar[start];
        ar[start] = ar[end];
        ar[end] = temp;
        start++;
        end--;

        rReverseAr(ar, size - 1);
    }       
}

The expected output should be when user entered 1 2 3 and it supposed to return 3 2 1. However, with these code, the output that I am getting is 2 3 1.

Any ideas?

Sergey Kalinichenko · Accepted Answer · 2015-09-26 11:43:41Z

7

Your code is almost right. The only problem is that instead of "shrinking" the array from both sides, you shrink it only from the back.

The recursive invocation should look like this:

rReverseAr(ar + 1, size - 2);

You do not need to increment start or decrement end, because their values are not used after modification.

answered Sep 26, 2015 at 11:43

Sergey Kalinichenko

729k85 gold badges1.2k silver badges1.6k bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

QWERTY Over a year ago

Alright thanks a lot! It works! However, can I know why for each recursion, you are increasing the array element position and at the same time, you are minusing the array size by 2? I mean like how +1 and -2 restrict the array shrinking from the back only?

Sergey Kalinichenko Over a year ago

@Denise Each recursive call passes a "sub-array" to the next level. This sub-array starts one element after the initial element (i.e. at ar+1 in pointer arithmetic syntax, or &ar[1] in array index syntax). The size of the sub-array is less than the size of the original array by 2, because the initial and the last elements have already been processed.

QWERTY Over a year ago

I see I see. Thanks a lot for the help!

rashedcs · Accepted Answer · 2017-12-27 13:48:35Z

0

A Simple way :

#include<stdio.h>
using namespace std;

void revs(int i, int n, int arr[])
{
  if(i==n)
  {
    return ;
  }
  else
  {
    revs(i+1, n, arr);
    printf("%d ", arr[i]);
  }
}


int main()
{
  int i, n, arr[10];
  scanf("%d", &n);
  for(i=0; i<n; i++)
  {
      scanf("%d", &arr[i]);
  }
  revs(0, n, arr);

  return 0;
}

Iterate array with recursion in C : link

edited Dec 27, 2017 at 13:48

answered Dec 27, 2017 at 12:28

rashedcs

3,7632 gold badges43 silver badges44 bronze badges

Comments

Chris Tang · Accepted Answer · 2020-03-01 06:36:13Z

0

What you are doing is to exchange values of the 1st and last elements and do the recursion.

Every time you should move your address to the next element as the starter for the next array exchange.

A possible way:

void rReverseAr(int ar[], int size){
      int buffer=ar[0]; 
      ar[0] = ar[size-1];
      ar[size-1] = buffer;
      if ((size!=2)&&(size!=1)) rReverseAr(ar+1,size-2);
}

answered Mar 1, 2020 at 6:36

Chris Tang

5747 silver badges18 bronze badges

Collectives™ on Stack Overflow

Reverse array with recursion in C programming

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related