C Program: Queue implementation using structure

C programming related to structures: Exercise-7 with Solution

Write a C program that implements a simple queue using a structure. The structure should contain an array representing the queue and front and rear indices. Include functions for enqueue and dequeue operations.

Sample Solution:

C Code:

#include <stdio.h>

// Define the structure "Queue"
#define MAX_SIZE 100

struct Queue {
    int arr[MAX_SIZE];
    int front, rear;
};

// Function to initialize the queue
void initializeQueue(struct Queue *queue) {
    queue->front = -1;
    queue->rear = -1;
}

// Function to check if the queue is empty
int isEmpty(struct Queue *queue) {
    return (queue->front == -1 && queue->rear == -1);
}

// Function to check if the queue is full
int isFull(struct Queue *queue) {
    return (queue->rear == MAX_SIZE - 1);
}

// Function to enqueue an element into the queue
void enqueue(struct Queue *queue, int value) {
    if (isFull(queue)) {
        printf("Queue is full. Cannot enqueue.\n");
        return;
    }

    if (isEmpty(queue)) {
        // If the queue is empty, set front and rear to 0
        queue->front = 0;
        queue->rear = 0;
    } else {
        // Increment rear circularly
        queue->rear = (queue->rear + 1) % MAX_SIZE;
    }

    // Enqueue the value
    queue->arr[queue->rear] = value;
    printf("Enqueued: %d\n", value);
}

// Function to dequeue an element from the queue
int dequeue(struct Queue *queue) {
    int value;

    if (isEmpty(queue)) {
        printf("Queue is empty. Cannot dequeue.\n");
        return -1; // Assuming -1 represents an error or empty queue
    }

    // Dequeue the value
    value = queue->arr[queue->front];

    if (queue->front == queue->rear) {
        // If the queue has only one element, set front and rear to -1
        queue->front = -1;
        queue->rear = -1;
    } else {
        // Increment front circularly
        queue->front = (queue->front + 1) % MAX_SIZE;
    }

    printf("Dequeued: %d\n", value);
    return value;
}

int main() {
    // Declare and initialize a queue
    struct Queue myQueue;
    initializeQueue(&myQueue);

    // Enqueue some elements
    enqueue(&myQueue, 100);
    enqueue(&myQueue, 200);
    enqueue(&myQueue, 300);

    // Dequeue elements
    dequeue(&myQueue);
    dequeue(&myQueue);

    // Enqueue more elements
    enqueue(&myQueue, 400);
    enqueue(&myQueue, 500);

    // Dequeue remaining elements
    dequeue(&myQueue);
    dequeue(&myQueue);

    return 0;
}

Output:

Enqueued: 100
Enqueued: 200
Enqueued: 300
Dequeued: 100
Dequeued: 200
Enqueued: 400
Enqueued: 500
Dequeued: 300
Dequeued: 400

Explanation:

In the exercise above:

• The "Queue" structure is defined with an array '(arr)', 'front', and 'rear' indices.
• Functions like "initializeQueue()", "isEmpty()", and "isFull()" are used for queue management.
• The "enqueue()" function adds an element to the rear of the queue.
• The "dequeue()" function removes an element from the front of the queue.
• The "main()" function demonstrates the usage of the queue operations.

Flowchart:

C Programming Code Editor:

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