C Program to Rotate an Array Left and Right

Introduction

Array rotation involves shifting the elements of an array either to the left or to the right by a specified number of positions. This guide will show you how to write a C program to rotate an array to the left and to the right.

Problem Statement

Create a C program that:

• Takes the size of the array as input from the user.
• Takes the elements of the array as input.
• Takes the number of positions to rotate the array.
• Rotates the array to the left and displays the result.
• Rotates the array to the right and displays the result.

Example:

• Input: Array = [1, 2, 3, 4, 5], Rotate by 2 positions
• Output: Left Rotation = [3, 4, 5, 1, 2], Right Rotation = [4, 5, 1, 2, 3]

Solution Steps

1. Include the Standard Input-Output Library: Use #include <stdio.h> to include the standard input-output library, which is necessary for using printf and scanf functions.
2. Write the Main Function: Define the main function, which is the entry point of every C program.
3. Declare Variables: Declare variables to store the array size, the array elements, and the number of positions to rotate.
4. Input the Array Size: Use scanf to take input from the user for the size of the array.
5. Input the Array Elements: Use a loop to take input from the user for the elements of the array.
6. Input the Number of Positions to Rotate: Use scanf to take input from the user for the number of positions to rotate.
7. Rotate the Array to the Left: Use a function or loop to perform the left rotation and display the result.
8. Rotate the Array to the Right: Use a function or loop to perform the right rotation and display the result.

C Program

#include <stdio.h>

/**
 * C Program to Rotate an Array Left and Right
 * Author: https://www.javaguides.net/
 */

// Function to rotate the array to the left by d positions
void rotateLeft(int arr[], int n, int d) {
    int temp[d];
    for (int i = 0; i < d; i++) {
        temp[i] = arr[i];
    }
    for (int i = 0; i < n - d; i++) {
        arr[i] = arr[i + d];
    }
    for (int i = 0; i < d; i++) {
        arr[n - d + i] = temp[i];
    }
}

// Function to rotate the array to the right by d positions
void rotateRight(int arr[], int n, int d) {
    int temp[d];
    for (int i = 0; i < d; i++) {
        temp[i] = arr[n - d + i];
    }
    for (int i = n - 1; i >= d; i--) {
        arr[i] = arr[i - d];
    }
    for (int i = 0; i < d; i++) {
        arr[i] = temp[i];
    }
}

// Function to print the array
void printArray(int arr[], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    // Step 1: Declare variables to hold the array size, elements, and rotation positions
    int n, d;

    // Step 2: Prompt the user to enter the size of the array
    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);

    // Step 3: Declare an array to hold the elements
    int arr[n];

    // Step 4: Input the array elements
    printf("Enter %d elements:\n", n);
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    // Step 5: Prompt the user to enter the number of positions to rotate
    printf("Enter the number of positions to rotate: ");
    scanf("%d", &d);

    // Step 6: Rotate the array to the left
    rotateLeft(arr, n, d % n);
    printf("Array after left rotation: ");
    printArray(arr, n);

    // Step 7: Rotate the array to the right
    rotateRight(arr, n, d % n);
    printf("Array after right rotation: ");
    printArray(arr, n);

    return 0;  // Step 8: Return 0 to indicate successful execution
}

Explanation

Step 1: Declare Variables

• The variable n is declared to store the size of the array. The variable d is used to store the number of positions to rotate the array.

Step 2: Input the Array Size

• The program prompts the user to enter the size of the array using printf. The scanf function reads the input and stores it in the variable n.

Step 3: Declare the Array

• The program declares an array arr of size n to hold the elements provided by the user.

Step 4: Input the Array Elements

• The program uses a for loop to take input for each element of the array. The loop iterates from 0 to n-1, reading the elements using scanf.

Step 5: Input the Number of Positions to Rotate

• The program prompts the user to enter the number of positions to rotate the array using printf. The scanf function reads the input and stores it in the variable d.

Step 6: Rotate the Array to the Left

• The function rotateLeft is used to rotate the array to the left by d positions:
  • The first d elements are temporarily stored in an array temp.
  • The remaining elements are shifted left by d positions.
  • The elements in temp are then placed at the end of the array.

Step 7: Rotate the Array to the Right

• The function rotateRight is used to rotate the array to the right by d positions:
  • The last d elements are temporarily stored in an array temp.
  • The remaining elements are shifted right by d positions.
  • The elements in temp are then placed at the beginning of the array.

Step 8: Display the Array

• The function printArray is used to print the elements of the array after the rotation.

Step 9: Return 0

• The return 0; statement indicates that the program executed successfully.

Output Example

Example:

Enter the number of elements in the array: 5
Enter 5 elements:
1
2
3
4
5
Enter the number of positions to rotate: 2
Array after left rotation: 3 4 5 1 2
Array after right rotation: 1 2 3 4 5

Example (Right Rotation):

Enter the number of elements in the array: 4
Enter 4 elements:
10
20
30
40
Enter the number of positions to rotate: 1
Array after left rotation: 20 30 40 10
Array after right rotation: 40 10 20 30

Conclusion

This C program demonstrates how to rotate an array to the left and right by a specified number of positions. It covers basic concepts such as arrays, loops, and array manipulation, making it a useful example for beginners learning C programming.