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Program source code is different from a project’s other kinds of documents. Normally, you expect requirements and design documents to eventually stabilize and remain mostly unchanged. In contrast, code changes continually, up to and sometimes even beyond the project’s official ending date.

That gives source code control systems a slightly different flavor than other kinds of document control systems. A requirements document might go through a dozen or so versions, but a code module might include hundreds or even thousands of changes. That means the tools you use to store code often don’t work particularly well with other kinds of documents and vice versa.

Source code is also generally line-oriented. Even in languages such as C# and Java, which are technically not line-oriented, programmers insert line breaks to make the code easier to read. If you change a line of source code, that change probably doesn’t affect the lines around it. Because of that, if you use a source code control system to compare two versions of a code file, it flags only that one line as changed.

In contrast, suppose you added the word “incontrovertibly” to the beginning of the preceding paragraph. That would make every line in the paragraph wrap to the following line, so every line in the paragraph would seem to have been changed. A document revision system, such as those provided by Microsoft Word or Google Docs, correctly realizes that you added only a single word. A source code control system might decide that you had modified every line in the paragraph.

What this means is that you should use separate tools to manage source code and other kinds of documents. This usually isn’t a big deal, and it’s easy to find a lot of choices online. (In fact, picking one that every developer can agree on may be the hardest part of using a source code control system.)

Ideally, a source code control system enables all the developers to use the code. If a developer needs to modify a module, the system checks out the code to that developer. Other developers can still use the most recently saved version of the code, but they can’t edit that module until the first developer releases it. (This avoids the race condition described earlier in this chapter.)

Some source code control systems are integrated into the development environment. They make code management so easy even the most advanced programmers don’t mess it up too often.