C Program to Reverse Elements of an Array

Reverse elements of an array in C

Here, in this page we will discuss the program to reverse elements of an array in C programming language. We are given with an array and need to reverse the elements. We will discuss various algorithms to reverse the array in efficient way.

C program to reverse an array

Here, in page we will discuss various method for reversing the array. Different methods are :

Method Discussed

  • Method 1: Just print the array in reverse order
  • Method 2: Actual in-place reversing of the original array
  • Method 3: Recursive in-place reversing of the original array

 

Example :

  • Input : arr[5] = [10, 20, 30, 40, 50]
  • Output : Array after reversing, arr[5] = [50, 40, 30, 20, 10]

We will discuss all of these methods one by one below –

C program to reverse an array

Method 1

For an array: arr

  • Run an iterative loop from the last index of the array
  • Print each item one by one arr[i]

Let’s see how it works below –

Method 1 Code in C

Run
#include <stdio.h>

void printReverse(int arr[], int len){
    
    for(int i = len - 1; i >= 0; i--)
        printf("%d ", arr[i]);
}

int main()
{
    int arr[] = {10, 20, 30, 40, 50, 60};
    
    int len = sizeof(arr)/sizeof(arr[0]);
    
    printf("Array in Reverse:\n");
    printReverse(arr, len);

    return 0;
}

Output

Array in Reverse:
60 50 40 30 20 10

Method 2

For an array: arr[] with length len.

  • Call a function void reverse(int arr[], int start, int end)
    • Intial calling as reverse(arr, 0, len-1);
  • Swap items at start & end indexes
  • Do start++ & end–
  • Stop when start & end indexes overlap one another
  • Print the array

Time and Space Complexity :

  • Time – Complexity : O(n)
  • Space-Complexity : O(1)

 

C Program to Reverse elements of an array

Method 2 Code in C

Run
#include <stdio.h>

void reverse(int arr[], int start, int end)
{
    while (start < end)
    {
        // swap arr[start] & arr[end]
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
        
        start++;
        end--;
    }
}

void display(int arr[], int len){
    
    for(int i = 0; i < len; i++)
        printf("%d ", arr[i]);
}

int main()
{
    int arr[] = {10, 20, 30, 40, 50, 60};
    
    int len = sizeof(arr)/sizeof(arr[0]);
    
    reverse(arr, 0, len-1);
    
    printf("Array in Reverse:\n");
    display(arr, len);

    return 0;
}

Output

Array in Reverse:
60 50 40 30 20 10

Method 3

In this method, we will use recursion. Call function reverseRecursive(int arr[], int start, int end)

Initially pass values of start = 0, end = len – 1

  • Function gets called as reverseRecursive(arr, 0, len-1);
  • In each recursive iteration swap arr[start] & arr[end]
  • Make further recursive calls as reverseRecursive(arr, start + 1, end – 1);
  • return when (start >= end)
  • Print the array

Time and Space Complexity :

  • Time – Complexity : O(n)
  • Space-Complexity : O(n), require stack to store the recursive calls.
Reverse elements of an array in C

Method 3 Code in C

Run
#include <stdio.h>

void reverseRecursive(int arr[], int start, int end)
{
    if (start >= end)
        return;
     
    int temp = arr[start];
    arr[start] = arr[end];
    arr[end] = temp;
     
    // recursive call to swap arr[start+1] & arr[end-1]
    reverseRecursive(arr, start + 1, end - 1);
}   

void display(int arr[], int len){
    
    for(int i = 0; i < len; i++)
        printf("%d ", arr[i]);
}

int main()
{
    int arr[] = {10, 20, 30, 40, 50, 60};
    
    int len = sizeof(arr)/sizeof(arr[0]);
    
    reverseRecursive(arr, 0, len-1);
    
    printf("Array in Reverse:\n");
    display(arr, len);

    return 0;
}

Output

Array in Reverse:
60 50 40 30 20 10

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array

4 comments on “C Program to Reverse Elements of an Array”


  • Shahid

    #include

    int main()
    {
    int a[10]={1,2,3,4,5,6,7,8,9,10};
    int b[10];
    int i,j,temp;
    for(i=0,j=9;i<j;j–,i++){
    temp=a[j];
    a[j]=a[i];
    a[i]=temp;
    }
    for(i=0;i<10;i++){
    printf("%d",a[i]);
    }
    }


  • Abhishek

    #include
    int main(){
    int a[5]={1,2,3,4,5};
    for (int i = 4; i >= 0; i–)
    {
    printf(“%d “,a[i]);
    }

    return 0;
    }


    • Rashmi Sri

      #include

      int main()
      {
      int n,a[100],i;
      printf(“enter the sie:”);
      scanf(“%d”,&n);
      printf(“enter the elements: “);
      for(i=0;i=0;i–)
      {
      printf(“%d “,a[i]);
      }
      return 0;
      }


      • Rashmi Sri

        #include

        int main()
        {
        int n,a[100],i;
        printf(“enter the size:”);
        scanf(“%d”,&n);
        printf(“enter the elements: “);
        for(i=0;i=0;i–)
        {
        printf(“%d “,a[i]);
        }
        return 0;