C/C++ :: Grep Hanging For Standard Input

So I'm working on an assignment that is roughly about implementing the grep utility, only it has to be programmed in C. The weird nuance of the assignment is that while we are implementing the utility, we can use grep only we cannot pass grep a filename to search through(we are supposed to pipe a line from the file to standard input so that grep can examine it there.) Anyways, when I reach execlp, it will print out what is in stdin from the terminal, but it hangs at that point and I have to press Ctrl+Z to exit. I probably have the most difficulty with using this function, so I came up with a smaller scale model to get the basics down. Anyways, here's my code:

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main(int argc, char* argv[]){

[Code] ....