array_queue.c

#include <stdio.h>

#define CAPACITY 5

int queue[CAPACITY];
int front = 0, rear = 0;

int isEmpty(void) {
        return front == rear;
}

int isFull(void) {
    return rear == CAPACITY;
}

/* --- enqueue --- */
void enqueue(int value) {
    if(isFull()){
        return;
    }
    queue[rear] = value;
    rear++;
    printf("Added: %d\n" , value);
}

/* --- dequeue --- */
int dequeue(void) {
    if(isEmpty()){
        return 0 ;
    }
    int x = queue[front];
    front++;
    return x;
}

/* --- peek --- */
int peek(void) {
    if(isEmpty()){
        return 0;
    }
    return queue[front];
}

int main(void) {
    enqueue(10);
    enqueue(20);
    enqueue(30);
    printf("%d\n" , peek());

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


    enqueue(40);
    enqueue(50);
    enqueue(60); // false overflow
    enqueue(70); // false overflow

    return 0;
}