Program to reverse an array using pointers

Last Updated : 13 Jan, 2023

Prerequisite : Pointers in C/C++ Given an array, write a program to reverse it using pointers . In this program we make use of * operator . The * (asterisk) operator denotes the value of variable . The * operator at the time of declaration denotes that this is a pointer, otherwise it denotes the value of the memory location pointed by the pointer .

reverse function : is used to reverse the array through pointers
swap function : is used to swap two memory contents
print function : will print the array

Approach : In reverse function we take two pointers one pointing at the beginning of the array, other pointing at end of the array. The contents of the memory location pointed by these two pointers are swapped and then the value of first pointer is increased and that of second pointer is decreased . Examples:

Input : array = 2, 4, -6, 5, 8, -1
Output : reverse_array = -1, 8, 5, -6, 4, 2

Input : array = 1, 4, -6, 8, -10, -12
Output : reverse_array = -12, -10, 8, -6, 4, 1

Implementation:

C++

// CPP program to reverse array 
// using pointers 
#include <iostream> 
using namespace std; 

// Function to swap two memory contents 
void swap(int* a, int* b) 
{ 
    int temp = *a; 
    *a = *b; 
    *b = temp; 
} 

// Function to reverse the array through pointers 
void reverse(int array[], int array_size) 
{ 

    // pointer1 pointing at the beginning of the array 
    int *pointer1 = array, 

        // pointer2 pointing at end of the array 
        *pointer2 = array + array_size - 1; 
    while (pointer1 < pointer2) { 
        swap(pointer1, pointer2); 
        pointer1++; 
        pointer2--; 
    } 
} 

// Function to print the array 
void print(int* array, int array_size) 
{ 

    // Length pointing at end of the array 
    int *length = array + array_size, 

        // Position pointing to the beginning of the array 
        *position = array; 
    cout << "Array = "; 
    for (position = array; position < length; position++) 
        cout << *position << " "; 
} 

// Driver function 
int main() 
{ 

    // Array to hold the values 
    int array[] = { 2, 4, -6, 5, 8, -1 }; 

    cout << "Original "; 
    print(array, 6); 

    cout << "Reverse "; 
    reverse(array, 6); 
    print(array, 6); 
    return 0; 
}

// C program to reverse array
// using pointers
#include <stdio.h>

// Function to swap two memory contents
void swap(int* a, int* b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}

// Function to reverse the array through pointers
void reverse(int array[], int array_size)
{
    // pointer1 pointing at the beginning of the array
    int *pointer1 = array,

        // pointer2 pointing at end of the array
        *pointer2 = array + array_size - 1;
    while (pointer1 < pointer2) {
        swap(pointer1, pointer2);
        pointer1++;
        pointer2--;
    }
}

// Function to print the array
void print(int* array, int array_size)
{
    // Length pointing at end of the array
    int *length = array + array_size,

        // Position pointing to the beginning of the array
        *position = array;
    printf("Array = ");
    for (position = array; position < length; position++)
        printf("%d ", *position);
}

// Driver function
int main()
{
    // Array to hold the values
    int array[] = { 2, 4, -6, 5, 8, -1 };

    printf("Original ");
    print(array, 6);

    printf("Reverse ");
    reverse(array, 6);
    print(array, 6);
    return 0;
}

//code contributed by dhanshriborse

Output

Original Array = 2 4 -6 5 8 -1 Reverse Array = -1 8 5 -6 4 2

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