Selecting font hight from within a program

[cahlucas]

Hi all,
In a new program I am making, it is necessary to have control over the font size on the screen. In home settings you can set the font size to small, medium and large. But apparently there is no variable associated with it, to set this up, at least I haven't been able to find one. I would really like to have control over this in connection with the alignment of text and lines on the screen. Does anyone know how I can set this from within a program? Sincerely, Karel.