C program to right rotate an array

Write a C program to right rotate an array by n position. How to right rotate an array n times in C programming. Logic to rotate an array to right by n position in C program.

Required knowledge

Basic C programming, If else, c-Arrays, What is function, C Loops

Right array rotation

Logic to right rotate an array

Below is the step by step descriptive logic to rotate an array to right by N positions.

  1. Read elements in an array say arr.
  2. Read number of times to rotate in some variable say N.
  3. Right rotate the given array by 1 for N times. In real right rotation is shifting of array elements to one position right and copying last element to first.

Algorithm to right rotate an array



 
Algorithm to right rotate an array
Begin:
    read(arr)
    read(n)
    For i?1 to n do
        rotateArrayByOne(arr)
    End for
End
rotateArrayByOne(arr[], SIZE)
Begin:
    last ? arr[SIZE - 1]
    For i ? SIZE-1 to 0 do
        arr[i] ? arr[i - 1]
    End for
    arr[0] ? last
End




Program to right rotate an array



 
/**
 * C program to right rotate an array
 */

#include <stdio.h>
#define SIZE 10 /* Size of the array */

void printArray(int arr[]);
void rotateByOne(int arr[]);


int main()
{
    int i, N;
    int arr[SIZE];

    printf("Enter 10 elements array: ");
    for(i=0; i<SIZE; i++)
    {
        scanf("%d", &arr[i]);
    }
    printf("Enter number of times to right rotate: ");
    scanf("%d", &N);

    /* Actual rotation */
    N = N % SIZE;

    /* Print array before rotation */
    printf("Array before rotationn");
    printArray(arr);

    /* Rotate array n times */
    for(i=1; i<=N; i++)
    {
        rotateByOne(arr);
    }

    /* Print array after rotation */
    printf("\n\nArray after rotation\n");
    printArray(arr);

    return 0;
}


void rotateByOne(int arr[])
{
    int i, last;

    /* Store last element of array */
    last = arr[SIZE - 1];

    for(i=SIZE-1; i>0; i--)
    {
        /* Move each array element to its right */
        arr[i] = arr[i - 1];
    }

    /* Copy last element of array to first */
    arr[0] = last;
}


/**
 * Print the given array
 */
void printArray(int arr[])
{
    int i;

    for(i=0; i<SIZE; i++)
    {
        printf("%d ", arr[i]);
    }
}



Output

Enter 10 elements array: 1 2 3 4 5 6 7 8 9 10
Enter number of times to right rotate: 3
Array before rotation
1 2 3 4 5 6 7 8 9 10
Array after rotation
8 9 10 1 2 3 4 5 6 7



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