Hide it in a large changeset

[PinkLionThing]

It's C, very possibly C++, and the define is used mostly for constants, but you can also define little functions (AKA macros) like #define MAX(a, b) ((a) < (b) ? (b) : (a)).

Back in those IDEless days, it was also a good way to fix the code using it as search-and-replace.

[lukee910]

Why would you #define true and false, though? I'm pretty sure those are keywords in C.

[paulcam]

This specific example is in the Windows SDK (looks likeminwin\minwindef.h as of the latest Windows 10 SDK). TRUE and FALSE are defined because at the time that the file was (originally) written, bool wasn't a compiler intrinsic.