1. typedef (Giving Types a Nickname)

The typedef keyword allows you to create an alias for an existing data type. It doesn't create a new type; it just gives a more descriptive name to an old one.

typedef unsigned long int ulong;
ulong population = 7000000000;

typedef int score;
score math = 95;

Why use it? It makes your code "self-documenting." It's clearer to see score than just int.

2. enum (The Set of Named Constants)

An enumeration is a user-defined type that consists of a set of named integer constants. By default, the first name is assigned the value 0, the next is 1, and so on.

enum Day { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday };
enum Day today = Wednesday; // today holds the value 2

Benefits of Enums

They make your code much more readable and less prone to errors. if (today == Sunday) is much harder to mess up than if (today == 6).

Custom Values in Enums

You can override the default values:

enum Level { LOW = 10, MEDIUM = 50, HIGH = 100 };

Combining Typedef and Enum

This is the standard way to create clean, boolean-like types in C:

typedef enum { FALSE, TRUE } bool;
bool isFinished = FALSE;

Use Enums for things that have a fixed, limited set of possibilities, like Colors, Game States (Menu, Loading, Playing), or Directions (North, South, East, West).