Flag

Vanilla Quake-C files make ample use of binary flags for entity properties as disparate as whether the entity is touching the ground to which weapons a player possesses.

Binary flags can be thought of as a bunch of switches that are either on or off pushed up next to each other. The player weapon system is a great example of this:

item flag-constant	integer value	2	binary value
IT_SHOTGUN	1	2^0	0000 0001
IT_SUPER_SHOTGUN	2	2^1	0000 0010
IT_NAILGUN	4	2^2	0000 0100
IT_SUPER_NAILGUN	8	2^3	0000 1000
IT_GRENADE_LAUNCHER	16	2^4	0001 0000
IT_ROCKET_LAUNCHER	32	2^5	0010 0000
IT_LIGHTNING	64	2^6	0100 0000

With these constants the game code can pack the weapon inventory into just 7 bits of data.

If the logic needs to check if a player has a rocket launcher:

if(player.items & IT_ROCKET_LAUNCHER)

If the logic needs to add the rocket launcher to the player's inventory:

player.items = players.items | IT_ROCKET_LAUNCHER;

If the logic needed to remove the rocket launcher from the player's inventory(provided that they have it:

if(player.items & IT_ROCKET_LAUNCHER)

player.items = players.items - IT_ROCKET_LAUNCHER;

Quake-C makes use of floats for this.