Server implementation for POSIX client-server program

posix_server.cpp

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

#define SIZE     2

int main() {
    int shmid;
    key_t key;
    char *shm, *s;

    key = 5678;

    shmid = shmget(key, SIZE, IPC_CREAT | 0666);
    shm = shmat(shmid, NULL, 0);

    s = shm;
    *s = '-';
    *s++;
    *s = '1';
    *s++;

    *s = NULL;


    while (1) {
        sleep(1);
        if (*shm != '7') {
            s = shm;
            *s = '-';
            *s++;
            *s = '1';
            *s++;
            *s = NULL;
        } else {
            exit(0);
        }
    }

    exit(0);
}