Question

How to implement queue using c

Posted on March 5, 2025
C (language)
Asked by d31e5fefa98d4e7f8e972df0460ce5

how to implement queue using c

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KFSys

Site Moderator

• March 5, 2025

Heya,

In C, a queue can be implemented using:

Arrays (Fixed-size queue, easy to implement but inefficient in some cases due to shifting)
Linked Lists (Dynamic size, efficient enqueue and dequeue operations)

Queue using an Array

#include <stdio.h>
#include <stdlib.h>

#define SIZE 5  // Define queue size

typedef struct {
    int items[SIZE];
    int front, rear;
} Queue;

// Initialize queue
void initQueue(Queue *q) {
    q->front = -1;
    q->rear = -1;
}

// Check if queue is full
int isFull(Queue *q) {
    return (q->rear == SIZE - 1);
}

// Check if queue is empty
int isEmpty(Queue *q) {
    return (q->front == -1 || q->front > q->rear);
}

// Enqueue operation
void enqueue(Queue *q, int value) {
    if (isFull(q)) {
        printf("Queue is full!\n");
        return;
    }
    if (q->front == -1) q->front = 0;
    q->rear++;
    q->items[q->rear] = value;
    printf("Inserted: %d\n", value);
}

// Dequeue operation
int dequeue(Queue *q) {
    if (isEmpty(q)) {
        printf("Queue is empty!\n");
        return -1;
    }
    int item = q->items[q->front];
    q->front++;
    return item;
}

// Display queue
void display(Queue *q) {
    if (isEmpty(q)) {
        printf("Queue is empty!\n");
        return;
    }
    printf("Queue: ");
    for (int i = q->front; i <= q->rear; i++)
        printf("%d ", q->items[i]);
    printf("\n");
}

// Main function
int main() {
    Queue q;
    initQueue(&q);

    enqueue(&q, 10);
    enqueue(&q, 20);
    enqueue(&q, 30);
    display(&q);

    printf("Dequeued: %d\n", dequeue(&q));
    display(&q);

    return 0;
}