An example of waitpid()

[csstudent123]

I want to modify this program using waitpid() only to output 

121 

#include <iostream>
#include <unistd.h>
using namespace std;
int main ()
{
    pid_t child_pid;
    int i=1;
    child_pid = fork ();
    if (child_pid != 0)
    {
        cout << i++<<endl;

        cout << i++<<endl;
    }
    else
        cout << i++<<endl;
        return 0;
    }


/////////////////////////////MY VERSION///////////////////////////////////

#include <iostream>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
using namespace std;
int main ()
{
    pid_t child_pid;
    int i=1;
    child_pid = fork ();
    if (child_pid != 0)
    {
        cout << i++<<endl;

        cout << i++<<endl;
    }
    else{
        waitpid(child_pid, NULL,WNOHANG);
        cout << i++<<endl;}

        return 0;
    }