Control one C program from another C program

ex.c

#include <stdio.h>
#include <bits/stdc++.h>
#include <unistd.h>

int main(){
    for(int i=0;;i++){
        printf("Ex.c : %d\n",i);
        sleep(1);
    }  
}
// Prints integers in intervals of 1 second

ex1.c

#include <stdio.h>
#include <bits/stdc++.h>
#include <unistd.h>

int main(){
    for(int i=0;;i++){
        printf("Ex2.c : %d\n",i);
        sleep(1);

        if(i == 3){
            return 5; // return status
        }
    }
}
// Prints integers in intervals of 1 second

Master_script.sh

#!/bin/sh

g++ ex1.c -o simp
g++ ex.c

./a.out & # Run the two C programs simultaneously
./simp

A=$? # Store return status of ex1.c
PID=$! # Store Process ID of the program going on
if [ $A -eq 5 ]; then
  kill $PID # Kill the continuing program
fi

# Run ./Master_script.sh
# What the program does is that if ex1.c terminates, it terminates ex.c as  well.