i am new to Linux......
Using C++. I have created a 3 Buttons. Each Button opens one Applications as a separate Process (
Say for Example Button1 opens Xterm, Button2 opens Firefox Button3 Opens Calculator
i have clicked on all 3 Buttons and all three applications are running.

i want to implement a feature like this, If i click on Button1 Again i want to make sure that Xterm that was already opened Get the Focus. i.e The I do not want to open a new Xterm But to bring the Xterm window that was previously opened on the top of all the open windows. How do i implement this?

Since the applications are started as Process i do not have a Control over them. in C++ how do i get the control of a window that is opened in linux

Check for running processes to see your application is running and then either start or switch focus. How to switch focus is dependent on what desktop environment/windows manager you use.