Back in the day....
The defacto rule of measurement for the number of printed lines for a 8.5x11 piece of paper was 65, I think. Karen is right - it depends on what language the program is in, is it just a function, or the whole program, etc... Personally, I'd doubt COBOL would be used to control a temperature [i]thingy[/], but regardless, a function could take up as few as 3 lines and as much as several pages. There are also tools to print more than one "page" per physical page - or as Karen suggested, rotated.
Plus - it would take a long time to do the printing.
The current project I'm working on (a multi-sensored, weather related project) has around 400,000 to 450,000 lines of code (C and C++).
After all this long-winded-ness; make it as big as you want for the story. The range is so great, just about anything will work.
(Still wondering why you would want to print it out in the first place...)
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