Find Reverse of an Array in C Using Functions

This article will demonstrate how to create a C program that uses a function to reverse an array. For instance, if "arr" is an array of three numbers like in:

arr [ 0 ] = 1
arr [ 1 ] = 2
arr [ 2 ] = 3

Then, by reversing the array we will have:

arr [ 0 ] = 3
arr [ 1 ] = 2
arr [ 2 ] = 1

In C, you may reverse an array in four different ways: with a for loop, pointers, recursion, or by writing a function.

Example:

#include < stdio.h >
#include < stdlib >
#include < conio.h >
#include < math >
// function to reverse an Array
void reverse ( int arr [ 10 ] , int n )
{
  int i , tmp ;
  for( i = 0 ; i < n / 2 ; i + + )
  {
    tmp = arr [ i ] ;
    arr [ i ] = arr [ n - 1 - i ] ;
    arr [ n - 1 - i ] = tmp ;
  }
}
int main ( )
{
  int arr [ 100 ] , i , size ;
  printf ( " ?nter size of array : " ) ;
  scanf ( " % d " , & size ) ;
  printf ( " ?nter the elements of the array : " ) ;
  for ( i = 0 ; i < size ; i + + )
    scanf ( " % d " , & arr [ i ] ) ;
  // call reverse function 
  reverse ( arr , size ) ;
  // display reversed array 
  printf ( " After reversing the array : " ) ;
  for ( i = 0 ; i < size ; i + + )
  {
    printf ( " % d " , arr [ i ] ) ;
  }
  return 0 ;
}

Output:

?nter size of array: 3  
?nter the elements of the array: 1 2 3
After reversing the array: 3 2 1
....................................
Process executed in 1.22 seconds
Press any key to continue.

Explanation

In the above example of a program in C, we have demonstrated how we can use function to reverse an array. We have created a user defined function reverse which takes the array and the size of the array as parameter and creates a tmp variable to swap the numbers.

In-Place Implementation

#include < stdio.h >
#include < stdlib >
#include < conio.h >
#include < math >
// Function to print contents of an array
void print ( int arr [ ] , int n )
{
	for ( int i = 0 ; i < n ; i + + ) {
		printf ( " % d " , arr [ i ] ) ;
	}
}
// Function to reverse elements of an array
void reverse ( int arr [ ] , int n )
{
	for ( int low = 0 , high = n - 1 ; low < high ; low + + , high - - )
	{
		int temp = arr [ low ] ;
		arr [ low ] = arr [ high ] ;
		arr [ high ] = temp ;
	}
}
int main ( void )
{
	int arr [ ] = { 1 , 2 , 3 , 4 , 5 } ;
	int n = sizeof ( arr ) / sizeof ( arr [ 0 ] ) ; 
	reverse ( arr , n ) ;
	print ( arr , n ) ;
	return 0 ;
}

Output:

5 4 3 2 1
.............
Process executed in 2.12 seconds
Press any key to continue.

Explanation

In the above example of a program in C, reading the items from both ends of the array and swapping them can be used to build a linear in-place algorithm, as shown in the example.

Another Example:

#include <stdio.h>
// Function to print contents of an array
void print(int arr[], int n)
{
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
}
// Function to reverse elements of an array
void reverse(int arr[], int i, int n)
{
    // base case: end of an array is reached or array index out-of-bounds
    if (i >= n) {
        return;
    }
    // store the next array element
    int value = arr[i];
    // reach the end of the array using recursion
    reverse(arr, i + 1, n); 
    // put elements in the call stack back into the array
    // in the correct order
    arr[n - i - 1] = value;
}
int main(void)
{
    int arr[] = { 1, 2, 3, 4, 5 };
    int n = sizeof(arr)/sizeof(arr[0]); 
    reverse(arr, 0, n);
    print(arr, n); 
    return 0;
}

Output:

5 4 3 2 1
....................
Process executed in 1.22 seconds
Press any key to continue.

Explanation

Another is a recurring system that puts the elements in a call stack before returning them to the same members in the correct order at the end of the repetition.

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