Implementation of the Queue using Array.

QueueArray.c

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

struct Queue {
  int size;
  int front;
  int rear;
  int *Q;
};

void create(struct Queue *q, int size) {
    q->size = size;
    q->front = q->rear = -1;
    q->Q = (int *) malloc(q->size*sizeof(int));
}

void enqueue(struct Queue *q, int value) {
    if (q->rear == q->size - 1)
        printf("Queue is Full");
    else {
        q->rear++;
        q->Q[q->rear] = value;
    }
}

int dequeue(struct Queue *q) {
    int x = -1;
    if (q->front == q->rear)
        printf("Queue is Empty\n");
    else
    {
        q->front++;
        x = q->Q[q->front];
    }
    return x;
}

void display(struct Queue q) {
    int i;
    for (i = q.front + 1; i <= q.rear; ++i) 
        printf("%d ", q.Q[i]);
    printf("\n");
}

int main() {
    struct Queue q;
    create(&q, 5);
    
    enqueue(&q, 10);
    enqueue(&q, 20);
    enqueue(&q, 30);
    
    display(q);
    
    printf("Dequeue: %i", dequeue(&q));
}