question about filenames

My program reads and writes external files which I have coded .mf files (mf stands for My Files). In windows explorer the files appear with a drab logo, does anyone know how to change the logo?

Also, is there anyway of making a filename of what the user inputs? The code currently is ->
mf = fopen("save.mf", "w+b");

I have tried -> mf = fopen(name.mf, "w+b"); and slight variations but I can't seem to crack it :(

To change the icon associated with a file:
go to my computer -> view -> folder options -> file types
and set it up.

What I actually meant was how do I make the Icons in my program so they come up on another computer that is running my program?
Sorry about the confusion.