#include <unistd.h>
#include <pthread.h>
#include <stdio.h>

#define THREADS 4

/* the function called for each thread */
void* f(void* idp) {
    int id = * (int*) idp;
    sleep(1);
    printf("Thread %d checking in!\n", id);
    pthread_exit(NULL);
}

int main() {
    /* an array of threads */
    pthread_t threads[THREADS];
    int ids[THREADS];

    int i;
    /* spawn the threads */
    for (i = 0; i < THREADS; i++) {
        ids[i] = i;
        pthread_create(&threads[i], NULL, f, &ids[i]);
    }

    /* wait for the threads to finish */
    for (i = 0; i < THREADS; i++) {
        pthread_join(threads[i], NULL);
    }

    printf("All threads finished!\n");

    pthread_exit(NULL);
}