Setting password for file?

Hello All,
I want set password for my file using C programming.
Before opening file i should get pop up saying 'enter the password'

Any suggestions would be great help.

Regards,
Siddu

well if you know how to open and close files this should be easy for you, what have you tried already? is it the actual password verifying and actions that is your problem or the fact you want a pop up box, which would make this a graphics as opposed to a logic problem for you, so which one is it?