jlPsiS - Online C Compiler & Debugging Tool

#include<stdio.h>

#define SIZE 5
int queue[SIZE];
int head, tail;

void enqueue(int value);
int dequeue(void);

int main(void)
{
    head = tail = 0;
    int i;
    enqueue(1);
    enqueue(2);
    dequeue();
    enqueue(3);
    dequeue();
    enqueue(4);
    enqueue(5);
    dequeue();
    enqueue(6);

    for(i = 0; i < SIZE; i++){
        printf("queue[%d] = %d\n", i, queue[i]);
    }

    return 0;
}

void enqueue(int value)
{
    if ((tail + 1) % SIZE == head) {
        return;
    }
    queue[tail] = value;
    tail = (tail + 1) % SIZE;
}
int dequeue(void)
{
    if (head == tail) {
        return -1;
    }
    int value = queue[head];
    queue[head] = 0;
    head = (head + 1) % SIZE;
    return value;
}