Programming

pid_t pid=fork();

if(pid > 0)
{
        fprintf(stderr, "I am in the parent\n");
}
else if(pid == 0)
{
        fprintf(stderr, "I am the child so should not fork again\n");
}
else
{
        perror("could not fork");
}

 #include <iostream>
  #include <stdio.h>
  #include <stdlib.h>
  #include <sys/types.h>
  #include <unistd.h>
  #include <sys/wait.h>
  using namespace std;
  int main(void)
  {
    pid_t pId;
    int status;
    int child1;
    int child2;
    int child3;
   
    if(pId = fork() > 0)
      {
        cout<<"This is the parent process, My PID is: "<<getpid()<<endl;
        pId = fork();
        wait(&status);
        
      }
    if(pId > 0)
      {
        pId = fork();
        wait(&status);
        exit(1);
      }
    else if(pId == 0)
  {
        child1 = getpid();
        cout<<"This is the first child process, My PID is: "<<getpid()<<endl;
        execl("/bin/ls", "ls", "-1", 0);
        exit(1);
      }
    else if(pId == 0)
      {
        child2 = getpid();
        cout<<"This is the second child process, My PID is: "<<getpid()<<endl;
        execl("/bin/ps", "-1f", 0);
       exit(1);
      }
    else if(pId == 0)
      {
        child3 = getpid();
        cout<<"This is the third child process, My PID is: "<<getpid()<<endl;
        exit(1);
      }
    exit(1);
  }
   child1 = getpid();
        cout<<"This is the first child process, My PID is: "<<getpid()<<endl;
        execl("/bin/ls", "ls", "-1", 0);
        exit(1);
      }
    else if(pId == 0)
      {
        child2 = getpid();
        cout<<"This is the second child process, My PID is: "<<getpid()<<endl;
        execl("/bin/ps", "-1f", 0);
        exit(1);
      }
    else if(pId == 0)
      {
        child3 = getpid();
        cout<<"This is the third child process, My PID is: "<<getpid()<<endl;
        exit(1);
      }
    exit(1);
  }

if(in_the_child)
{
        // runs in the child
        command1();
        command2();
        command3();
        // child quits so it doesn't run parent_stuff();
        exit(0);
}

// Only the parent will run this stuff
parent_stuff();
parent_stuff();
parent_stuff();

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

int main(void)
{
        pid_t pid[3];
        int n;

        for(n=0; n<3; n++)
        {
                pid[n]=fork();

                if(pid[n] == 0) // if we are the child, exit immediately
                {       exit(0);        }
        }

        printf("Parent pid: %d\n", (int)getpid());

        for(n=0; n<3; n++)
        {
                int status;
                printf("Child %d pid: %d\n", n, pid[n]);
                // We must wait for the child
                waitpid(pid[n], &status, 0);
        }
}