Program to Reverse a String using Pointers

Last Updated : 07 Aug, 2024

Given a string, the task is to reverse this String using pointers. Examples:

Input: Geeks
Output: skeeG

Input: GeeksForGeeks
Output: skeeGroFskeeG

Approach: This method involves taking two pointers, one that points at the start of the string and the other at the end of the string. The characters are then reversed one by one with the help of these two pointers. Program:

C++

#include <bits/stdc++.h>
using namespace std;

void reverseString(char* str) 
{ 
    int l, i; 
    char *begin_ptr, *end_ptr, ch; 

    // Get the length of the string 
    l = strlen(str); 

    // Set the begin_ptr
    // initially to start of string 
    begin_ptr = str;

    // Setting end_ptr initially to
    // the end of the string
    end_ptr = str + l - 1;

    // Swap the char from start and end 
    // index using begin_ptr and end_ptr 
    for (i = 0; i < l / 2; i++) { 
      
        // swap character 
        ch = *end_ptr; 
        *end_ptr = *begin_ptr; 
        *begin_ptr = ch; 

        // update pointers positions 
        begin_ptr++; 
        end_ptr--; 
    } 
} 

int main() 
{ 
    // Define a string
    char str[100] = "GeeksforGeeks";
  
  	cout << "Original String: " << str << endl;

    // Reverse the string 
    reverseString(str); 

    cout << "Reverse of the string: " << str << endl; 

    return 0; 
}

#include <stdio.h>
#include <string.h>

// Function to reverse the string
// using pointers
void reverseString(char *str)
{
    int l, i;
    char *begin_ptr, *end_ptr, ch;

    // Get the length of the string
    l = strlen(str);

    // Setting the begin_ptr
    // to start of string
    begin_ptr = str;

    // Setting the end_ptr the end of
    // the string
    end_ptr = str + l - 1;

    // Swap the char from start and end
    // index using begin_ptr and end_ptr
    for (i = 0; i < l / 2; i++)
    {

        // swap character
        ch = *end_ptr;
        *end_ptr = *begin_ptr;
        *begin_ptr = ch;

        // update pointers positions
        begin_ptr++;
        end_ptr--;
    }
}

int main()
{
    // Define the String
    char str[100] = "GeeksforGeeks";

    // Reverse the string
    reverseString(str);

    printf("Reverse of the string: %s\n", str);

    return 0;
}

Output

Enter a string: GeeksForGeeks
Reverse of the string: skeeGroFskeeG

Time Complexity: O(N), where N represents the length of the given string.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Program to reverse an array using pointers

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Program to Reverse a String using Pointers

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