Circular Queue

#include <stdio.h>

typedef struct {
    int data[4];
    int head;
    int size;
} Queue;

int push(Queue *queue, int value) {
    if (queue->size == 4) return 0;
    int tail = (queue->head + queue->size) % 4;
    queue->data[tail] = value;
    ++queue->size;
    return 1;
}

int pop(Queue *queue, int *value) {
    if (queue->size == 0) return 0;
    *value = queue->data[queue->head];
    queue->head = (queue->head + 1) % 4;
    --queue->size;
    return 1;
}

int main(void) {
    Queue queue = {{0}, 0, 0};
    int value;
    push(&queue, 7);
    push(&queue, 9);
    pop(&queue, &value);
    printf("%d\n", value);
}

#include <iostream>
#include <queue>

int main() {
    std::queue<int> values;
    values.push(7);
    values.push(9);
    std::cout << values.front() << '\n';
    values.pop();
}