C++ :: Give Output To Child Process

I'm trying to build a basic shell for Unix. This is the code I use to create a new process:

Code:
pid = fork();
if (pid == 0) {
setpgrp();
complexCommand(argv, isComplex);

[code] .....

Where complexCommand is a function that handles the command (uses execvp after generating the correct string out of argv). My problem is that after if while in the shell I use a program that needs to print to the screen and handle input, it doesn't work as expected. To test this, I built this small program:

Code:
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
int main() {
int x1, x2;

[code] ....

And when I use the shell I built to run it, the output is only "Enter 2 numbers" for one time. It doesn't print the result, or anything else. Is there anything I need to do in the parent process (my shell in this case) to give the child the output?