Start up program

How do I make my program start up when I switch windows on using c code.

You can't make your program start itself up, you have to make Windows start your program up by placing it in Window's /startup directory. There might be other ways to do it but i can't think of them right at this moment in eternity. You could try searching if you hav'nt already or even consider using Google.

You can also install your code as a "service" which will be started as a part of the OS when the system boots, this is, however, NT cored system specific - i.e. it won't work with Windows 9x/ME systems.