Assuming c++ program is compiled already you will have to use the php system() function to execude system commands. You can also use php's exec() function as well. For both of them php's installation must allow you this. As an example. You can take as example a single script to execute xmms player on linux from php using exec() or system() variables:
echo ' Executing XMMS ';
// note you could use system too!
//echo system( '/usr/bin/xmms --play icould.wav', $retval );
exec ('/usr/bin/xmms --play icould.wav');
system() variable doesnt return by default the executed command output so that's the $retval purpose.
Hope it helps