What are binary semaphores?

main.c

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <semaphore.h>

#define THREAD_NUM 1

sem_t semFuel;
pthread_mutex_t mutexFuel;

int *fuel;

void* routine(void* args) {
    *fuel += 50;
    printf("Current value is %d\n", *fuel);
    sem_post(&semFuel);
}

int main(int argc, char *argv[]) {
    pthread_t th[THREAD_NUM];
    fuel = malloc(sizeof(int));
    *fuel = 50;
    pthread_mutex_init(&mutexFuel, NULL);
    sem_init(&semFuel, 0, 0);
    int i;
    for (i = 0; i < THREAD_NUM; i++) {
        if (pthread_create(&th[i], NULL, &routine, NULL) != 0) {
            perror("Failed to create thread");
        }
    }
    sem_wait(&semFuel);
    printf("Deallocating fuel\n");
    free(fuel);

    for (i = 0; i < THREAD_NUM; i++) {
        if (pthread_join(th[i], NULL) != 0) {
            perror("Failed to join thread");
        }
    }
    pthread_mutex_destroy(&mutexFuel);
    sem_destroy(&semFuel);
    return 0;
}