why semop() function call is not working?

Question

semop function call is not working on the linux .I am running this program on 2 terminals so what I am trying to do is that allowing one instance of program into critical section from one terminal and another instance from terminal 2 will wait before critical section till first comes out, but semop is not working so both are entering into the critical section at the same time ,so what i am missing here , can anybody resolve this issue?

#include<stdio.h>
#include<unistd.h>
#include<sys/sem.h>
#include<sys/types.h>
#include<sys/ipc.h>

int main(void)
{
int key,semid;
key=ftok(" ",'a');
struct sembuf buf={0,-1,0};
semid= semget(key,1,0);
printf("Before entering into the critical section\n");
printf("Waiting for unlock\n");
semop(semid, &buf,1);
printf("Enter the critical section\n");
printf("Enter to unlock\n");
getchar();
buf.sem_op=1;
semop(semid, &buf,1);
}```

Answer 1

I think you need to add another getchar() under the already existing one.