Chapter 1. Introduction

I regret to report that I've just recently looked again at my programs for prime factors and tic-tac-toe, and they are entirely free of any sort of comments or documentation.

—Donald E. Knuth

Software source code is the definitive medium for communicating a program's operation and for storing knowledge in an executable form. You can compile source code into an executable program, you can read it to understand what a program does and how it works, and you can modify it to change the program's function. Most programming courses and textbooks focus on how to write programs from scratch. However, 40% to 70% of the effort that goes into a software system is expended after the system is first written. That effort invariably ...

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