[SysPro] Fork, Wait, Zombie

// fork.c
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
    pid_t pid; char *msg; int n;

    printf("fork program starting\n");
    pid = fork();
    switch(pid)
    {
        case -1: exit(1);
        case 0: msg = "Child!\n"; n = 45; break;
        default: msg = "Parent!\n"; n = 3; break;
    }

    for (; n>0; n--) { puts(msg); sleep(1); }
    exit(0);
}

// wait.c
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
    pid_t pid; char *msg; int n;
    printf("fork program starting\n");
    pid = fork();
    switch(pid)
    {
        case -1: exit(1);
        case 0: msg = "Child!\n"; n = 45; break;
        default: msg = "Parent!\n"; n = 3; break;
    }
    for (; n>0; n--) { puts(msg); sleep(1); }
    if (pid)
    {
        int stat_val; pid_t child_pid;
        child_pid = wait(&stat_val);
        printf("Child has finished: PID = %d\n",
               child_pid);
        if (WIFEXITED(stat_val))
            printf("Child exited with code %d\n",
                   WEXITSTATUS(stat_val));
        else
            printf("Child terminated abnormally\n");
    }
    exit(0);
}

// zombie.c
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
    pid_t pid; char *msg; int n;
    printf("fork program starting\n");
    pid = fork();
    switch(pid)
    {
        case -1: exit(1);
        case 0: msg = "Child!\n"; n = 3; break;
        default: msg = "Parent!\n"; n = 45; break;
    }
    for (; n>0; n--) { puts(msg); sleep(1); }

    if (pid)
    {
        int stat_val; pid_t child_pid;
        child_pid = wait(&stat_val);
        printf("Child has finished: PID = %d\n", child_pid);
        if (WIFEXITED(stat_val))
            printf("Child exited with code %d\n", WEXITSTATUS(stat_val));
        else
            printf("Child terminated abnormally\n");
    }
    exit(0);
}