Complex programs
Learning programming not only teaches you how to write code, but it also helps you develop a better eye for reading code, both your own and others'. In this week, we have explored the use of lists and practiced separating the user interface (UI) from the program logic.
The following is from On the role of scientific thought by Dutch computer scientist Edsger W. Dijkstra .
Let me try to explain to you, what to my taste is characteristic for all intelligent thinking. It is, that one is willing to study in depth an aspect of one's subject matter in isolation for the sake of its own consistency, all the time knowing that one is occupying oneself only with one of the aspects. We know that a program must be correct and we can study it from that viewpoint only; we also know that it should be efficient and we can study its efficiency on another day, so to speak. In another mood we may ask ourselves whether, and if so: why, the program is desirable. But nothing is gained - on the contrary! - by tackling these various aspects simultaneously. It is what I sometimes have called "the separation of concerns", which, even if not perfectly possible, is yet the only available technique for effective ordering of one's thoughts, that I know of. This is what I mean by "focusing one's attention upon some aspect": it does not mean ignoring the other aspects, it is just doing justice to the fact that from this aspect's point of view, the other is irrelevant. It is being one- and multiple-track minded simultaneously.
The essence of Dijkstra's message is that problem areas in a program must be separated from each other. This is precisely what we have achieved through object-oriented programming and by separating the user interface (UI) from the program logic. Each problem area has been isolated into its own distinct part. This can also be viewed through the lens of program responsibilities. In his blog Robert "Uncle Bob" C. Martin describes the term "single responsibility principle":
When you write a software module, you want to make sure that when changes are requested, those changes can only originate from a single person, or rather, a single tightly coupled group of people representing a single narrowly defined business function. You want to isolate your modules from the complexities of the organization as a whole, and design your systems such that each module is responsible (responds to) the needs of just that one business function.
[..in other words..] Gather together the things that change for the same reasons. Separate those things that change for different reasons.
Maintaining proper program structure and adhering to good naming principles leads to clean code. As you gain more experience in coding, you will learn that each part of a program can be assigned a clear area of responsibility.