C Program to Reverse an Array using Pointers

In this article, we will write a C program to reverse an array using pointers. The program walks through the given array, reverses it, and prints the reversed array on the output screen.

Sample Example:

Original Array: 1 2 3 4 5
Reversed Array: 5 4 3 2 1

Before we write the actual program, let’s have a look at pointers in C programming language.

In C programming, a pointer is a variable that stores the memory address of another variable. It is declared by the * symbol.

For example, int *ptr declares a pointer of type int. This means that the pointer *ptr can hold the memory address of an integer type of variable.

To reverse an array using pointers in C, we can use the following algorithm:

1. Initialize two pointers *start and *end of the same data type as of the array.
2. Initially, assign the array itself to the pointer *start so that it can point to the first element of the array.
3. Add the (size of the array – 1) to the array and assign it to the pointer *end so that it can point to the last element of the array.
4. Run a while loop until the pointers *start and *end point to the same address.
5. Inside the while loop, swap the elements pointed to by *start and *end.
6. Increment *start by 1 so that it can point to the next element of the array and decrement *end by 1 so that it can point to the previous element of the array in each iteration of the while loop.
7. Continue the while loop until *start becomes equal to *end.

Here is the implementation of the above algorithm:

// C Program to reverse an array using pointers

#include <stdio.h>

int main() {
	
	// Initialize the array
	int arr[] = {1, 2, 3, 4, 5};
	int *start, *end, temp;
	
	// Calculate the size of the array
	int length = sizeof(arr)/sizeof(arr[0]);
	
	printf("Original Array: ");
	for(int i = 0; i < length; i++){
		printf("%d ", arr[i]);
	}
	
	start = arr;  // Points to first element of array
	end = arr + (length - 1);  // Points to last element of array
	
	// Reverse the array
	while(start < end){
		
		// Swap items stored at *start and *end
		temp = *start;
		*start = *end;
		*end = temp;
		
		start++;  // Move to next address
		end--;	// Move to previous address
	}
	
	printf("\nReversed Array: ");
	for(int i = 0; i < length; i++){
		printf("%d ", arr[i]);
	}
	
	return 0;

}

Output:

Original Array: 1 2 3 4 5
Reversed Array: 5 4 3 2 1

You have to make sure that the data type of the pointers should also be same as the array itself. For example, if you have an array of char type, the pointers should also be of char data type.

I hope you will find this article helpful. Thanks for reading!