If you want to access program files folder dynamically than .NET framework provide you special variable to access Program Files folder Dynamically called Environment variable. And its easy also along with Program files you also can access other special windows folder like My Docuemnt, My Music etc.
Lets see an example
// to access program files folder
Environment.SpecialFolder.ProgramFiles
//To acess MyMusic folder
Environment
.SpecialFolder.MyMusic
Similarly you can access other folders also