As mentioned above, you are required to present the complete source code using the literate programming style. In some cases you may find it easier to present design decisions and source code if you combine them in a single section. This is permitted.
Keep in mind the flexibility the literate programming style permits: you can present the most important parts of your code first, followed by the details, assembling the parts into an order acceptable to the compiler in an "overview" or "outline" part (which can come either before or after the other parts). You may even relegate nitty-gritty details to an appendix so they don't make the main discussion too long.