enum

Learn to define named constants with enum.

enum

An enum lists named integer constants. It's the basic way to replace magic numbers with meaningful names; it improves code readability.

Example: enum Color { RED, GREEN, BLUE };. Here RED = 0, GREEN = 1, BLUE = 2. By default the first constant is 0 and each next one increments. Usage: enum Color c = GREEN; printf("%d\n", c); prints 1. enum constants are substituted at compile time; they take no memory at runtime. That's why they're efficient and common.

Explicit values

You can give enum constants explicit values beyond the default. This is useful to define custom code lists.

Example: enum Level { LOW = 10, MEDIUM = 20, HIGH = 30 };. Now LOW is 10. Or partial explicit: enum Code { A = 1, B, C = 10, D };. Here B = 2 (increments from A), C = 10 (explicit), D = 11 (increments from C). This flexibility is handy when defining protocol codes and error numbers. Still, avoid complex value layouts to keep readability.

Exercise Pick a color with enum and print

Define enum Color with RED, GREEN, BLUE. In main, write enum Color c = GREEN; and print with printf("%d\n", c);.

Show example solution

#include <stdio.h>

enum Color { RED, GREEN, BLUE };

int main(void) {
    enum Color c = GREEN;
    printf("%d\n", c);
    return 0;
}

Test yourself

Match enum constants to values

enum Color

Enum type
RED

0 (default)
GREEN

1
BLUE

2
What's the default first value of an enum?
- 1
- -1
- 0
- Unlimited
Show answer

0 — The first enum constant defaults to 0.

Complete the enum constant

enum Color { RED, ____, BLUE };

Show answer

enum Color { RED, GREEN, BLUE };

Next lesson: Struct and union

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