Reverse an Array in C++

The many approaches to reverse an array in the C++ programming language will be discussed in this section. The term "reverse of an array" refers to changing the order of the elements in a given array. This approach turns the array's final element into the first, and the first element into the last. The procedure, however, continues until all of the array's letters or components have been entirely reversed.

For example, the array has items such as 'J', 'A', 'V', 'A', and when we reverse all of the elements of an array, we get 'J', 'A', 'V', 'A'. As a result, all of the characters in the array are reversed in this manner.

In the C++ programming language, there are several techniques to retrieve the reverse array.

• Using for loop, reverse an array.
• The reverse ( ) method may be used to reverse an array.
• Using the user-defined function, reverse an array.
• Using the pointers, reverse an array.
• Using the Recursion function, reverse an array.

Using for loop to reverse an array

Let us loot at an example of a program in C++:

#include < iostream >  
#include < bits/stdc++.h >
#include < stdlib >
#include < stdio >
using namespace std ;  
int main ( )  
{  
    int arr [ 50 ] , num , temp , i , j ;  
    cout << " Please, enter the total no. you want to enter: " ;  
    cin >> num ;  
    // use for loop to enter the numbers   
    for ( i = 0 ; i < num ; i++ )  
    {  
        cout << " Enter the element " << i + 1 << ": " ;  
        cin >> arr [ i ] ;  
    }  
    for ( i = 0 , j = num - 1 ; i < num / 2 ; i++ , j-- )  
    {     
        temp = arr [ i ] ;  
        arr [ i ] = arr [ j ] ;  
        arr [ j ] = temp ;  
    }  
    cout << "\n Reverse all elements of the array: " << endl ;  
    // use for loop to print the reverse array  
    for ( i = 0 ; i < num ; i++ )  
    {  
        cout << arr [ i ] << " " ;  
    }  
    return 0 ;  
}

OUTPUT:

Please, enter the total no. you want to enter: 6
 Enter the element 1: 78
 Enter the element 2: 12
 Enter the element 3: 54
 Enter the element 4: 24
 Enter the element 5: 7
 Enter the element 6: 90


Reverse all elements of the array:
90 7 24 54 12 78
………………………………………………………………………
Process executed in 0.11 seconds
Press any key to continue.

Explanation:

In the above program in C++, we are using for loop to reverse an array of integer in which we are iterating till num and using a swap function using a temp variable to swap the numbers.

The reverse() method to reverse an array.

Let's look at an example of utilizing the reverse () function in C++ to output the reverse of an array:

#include < iostream >  
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >
#include < algorithm >  
using namespace std ;  
// declare disp ( ) function   
void disp ( int arr1 [ ] , int num )  
{  
    int i ;  
    // use for loop to iterate the characters  
    for ( i = 0 ; i < num ; i++ )  
    {  
        cout << arr1 [ i ] << " " ;  
    }  
}  
// define reverse ( ) function to reverse the array elements  
void reverse ( int arr1 [ ] , int num )  
{  
    reverse ( arr1 , arr1 + num ) ;   
}  
int main ( )  
{  
    // declare and initialize an array  
    int arr1 [ ] = { 34 , 78 , 21 , 90 , 5 , 2 } ;  
    int num = sizeof ( arr1 ) / sizeof ( arr1 [ 0 ] ) ;  
    // call reverse function and pass parameters  
    reverse ( arr1 , num ) ;  
    disp ( arr1 , num ) ; /* call disp ( ) function to print the revrse array. */  
    return 0 ;   
}

OUTPUT:

2 5 90 21 78 34
……………………..
Process executed in 0.11 seconds
Press any key to continue.

Explanation:

In the above example in C++, we are using a reverse function which takes an array of integer and a num as a parameter which performs the reverse function in C++.

The user-defined function to reverse an array

Let's look at an example of utilizing the user-defined in C++ to display the reverse of array members:

#include < iostream >  
#include < bits/stdc++.h >
#include < algorithm >
#include < stdio >
#include < stdlib >
using namespace std ;  
void ArrRev ( int [ ] , int ) ;  
int main ( )  
{  
    int arr [ 50 ] , num , i , j , temp ;  
    cout << " Number of elements to be entered: " << endl ;  
    cin >> num ;  
    cout << " Enter the array elements: " << endl ;  
    // use for loop to enter the elements  
    for ( i = 0 ; i < num ; i++ )  
    {  
        cin >> arr [ i ] ;  
    }  
    cout << " Elements are: \n" ;  
    // display entered elements in array  
    for ( i = 0 ; i < num ; i++ )  
    {  
        cout << arr [ i ] << " " ;  
    }  
    ArrRev ( arr , num ) ; // call function  
    cout << " \n The reverse of the given array is: \n" ;  
    // use for loop to print the reverse array elements  
    for ( i = 0 ; i < num ; i++ )  
    {  
        cout << arr [ i ] << " " ;  
    }  
    cout << endl ;  
    return 0 ;  
}  
void ArrRev ( int ar[], int a2)  
{  
    int i, j, temp;  
    j = a2 - 1;  
    for ( i = 0; i < j; i++, j--)  
    {  
        temp = ar[i];  
        ar[i] = ar[j];  
        ar[j] = temp;  
    }  
}

OUTPUT:

Number of elements to be entered:
7
 Enter the array elements:
45
32
89
21
78
34
65
Elements are:
45 32 89 21 78 34 65
The reverse of the given array is:
65 34 78 21 89 32 45
………………………………………………..
Proce3ss executed in 0.22 seconds
Press any key to continue.

Explanation:

In the above example of a program in C++, we used a user define function ArrRev which takes an array of type integer and the size of the array and also using for loop to display the elements of the array.

Using the pointers to reverse an array

Let's look at an example that shows how to reverse array members in C++ using pointers:

#include < iostream >  
#include < bits/stdc++ >
#include < stdlib >
#include < stdio >
using namespace std ;  
int main ( )  
{  
    // declare the size of array  
    int arr [ 50 ] , arr2 [ 50 ] ;  
    int * ptr , i , num ;  
    cout <<" No. of array elements to be entered: "<< endl ;  
    cin >> num ;     
      
    cout <<" Enter the elements: " ;  
    // use for loop to insert the array elements  
    for ( i = 0 ; i  <  num ; i++ )  
    {  
        cin >> arr [ i ] ;  
    }  
    ptr = & arr [ 0 ] ;  
    cout <<" Entered elements of the array are: \n" <<endl ;  
    for ( i = 0 ; i < num ; i++ )  
    {  
        cout << "\t" << * ptr ;  
        ptr++ ;  
    }  
    ptr-- ; // decrement ptr  
    for ( i = 0 ; i < num ; i++ )  
    {  
        arr2 [ i ] = * ptr ;  
        ptr-- ;  
    }  
    ptr = & arr2 [ 0 ] ;  
    for ( i = 0 ; i < num ; i++ )  
    {  
        arr [ i ] = * ptr ;  
        ptr++ ; // increment ptr  
    }  
    ptr = & arr [ 0 ] ; // ptr hold the base address of arr [ 0 ]  
    cout <<" \n The reversed array elements are: \n " << endl ;  
      
    // print the array elements using ptr  
    for ( i = 0 ; i < num ; i++ )  
    {  
        cout <<" \t " << * ptr << endl ;  
        ptr++ ;  
    }  
    return 0 ;  
}  

OUTPUT

No. of array elements to be entered:
6
 Enter the elements: 45
32
89
63
4
6
Entered elements of the array are: 
45      32      89      63      4       6
The reversed array elements are: 
         6
         4
         63
         89
         32
         45
…………………………………………………
Process executed in 0.11 seconds
Press any key to continue.

Explanation:

In the above example of a program in C++, we have used pointer ptr which stores the address of array at index zero and using for loop it stores all the address of the elements present in the array and incrementing ptr in each iteration.

Using the Recursion function to reverse an array

Let's use the recursion function in C++ to develop a program that reverses the array items:

#include < iostream >  
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >
#include < algorithm > 
using namespace std ;  
// initialize array  
int arr [ ] = { 20 , 34 , 5 , 8 , 1 , 78 } ;  
// size of the array  
int size = sizeof ( arr ) / sizeof ( arr [ 0 ] ) ;  
void reverseArr ( int arr [ ] , int num )  
{  
    // check the size of array  
    if ( num == size )  
        return ;  
    // extract array elements  
    int elem = arr [ num ] ;  
    // recursively calls the next element of the array  
    reverseArr ( arr , num + 1 ) ;  
    // assigning elements  
    arr [ size - num - 1 ] = elem ;  
}  
int main ( )  
{  
    int i ;  
    // call recursive function (start from first elements  
    cout << " Original elements of the arrays " << endl ;  
    for ( int i = 0 ; i < size ; i++ )  
    {  
        cout << arr [ i ] << " " ;  
    }  
    reverseArr ( arr , 0 ) ;  
    cout << " \n Reverse elements of the array are: " << endl ;  
    // display the array elements  
    for ( int i = 0 ; i < size ; i++ )  
    {  
        cout << arr [ i ] << " " ;  
    }  
    return 0 ;  
}  

OUTPUT:

Original elements of the arrays
20 34 5 8 1 78
Reverse elements of the array are:
78 1 8 5 34 20
………………………………………………
Process executed in 0.11 seconds
Press any key to continue.

Explanation:

In the above example of a program in C++, we have used the concept of recursion to reverse the elements of an array. First we are printing the original array by applying for loop and displaying it, then recursively passing arr and 0 to the function reverseArr.

Let us look at  another example to better understand:

// Recursive C++ program to reverse an array
#include < bits/stdc++.h >
#include < iostream >
#include < stdlib >
#include < stdio >
using namespace std ; 
/* Function to reverse arr [ ] from start to end*/
void rvereseArray(int arr [ ] , int start , int end )
{
	if ( start >= end )
	return ; 
	int temp = arr [ start ] ;
	arr [ start ] = arr [ end ] ;
	arr [ end ] = temp ; 
	// Recursive Function calling
	rvereseArray ( arr , start + 1 , end - 1 ) ;
}	
/* Utility function to print an array */
void printArray(int arr[], int size)
{
for ( int i = 0 ; i < size ; i++ )
cout << arr [ i ] << " " ; 
cout << endl ;
}
/* Driver function to test above functions */
int main ( )
{
	int arr [ ] = { 1 , 2 , 3 , 4 , 5 , 6 } ; 
	// To print original array
	printArray ( arr , 6 ) ; 
	// Function calling
	rvereseArray ( arr , 0 , 5 ) ; 
	cout << "Reversed array is" << endl ; 
	// To print the Reversed array
	printArray ( arr , 6 ) ; 
	return 0 ;
}

OUTPUT:

1 2 3 4 5 6 
Reversed array is 
6 5 4 3 2 1

Explanation

In the above example of a program in C++, we demonstrated another way of recursive method to find the reverse of an array. We are creating a temp variable which does our swapping then we recursively calling start plus one and end minus one which moves both of the variable iterator from left to right and visa versa.

Miscellaneous Program

Using Stack Data Structure:

#include < iostream >
#Include < bits/stdc++.h >
#include < stdlib >
#include < stdio >
#include < stack >
using namespace std ; 
// Utility function to print contents of an array
void print ( int arr [ ] , int n )
{
	for ( int i = 0 ; i < n ; i++ ) {
		cout << arr [ i ] << " " ;
	}
}
// Utility function to reverse elements of an array
void reverse ( int arr [ ] , int n )
{
	// create an empty stack of integers
	stack < int > stack ; 
	// push each array element into a stack
	for ( int i = 0 ; i < n ; i++ ) {
		stack . push ( arr [ i ] ) ;
	}
	// start from index 0
	int index = 0 ; 
	// pop values from the stack until it becomes empty
	while ( ! stack . empty ( ) )
	{
		// assign each popped item back to the original array
		arr [ index++ ] = stack.top ( ) ;
		stack . pop ( ) ;
	}
}
int main ( )
{
	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 0.11 seconds
Press any key to continue.

Explanation

In the above example of a program in C++, we have used stack data structure. We have created a stack and using the push function in stack STL we pushed our array elements in stack one by one then we bring top to the top element in our stack and popping it out one by one which gives our reversed array.