C Enumerations (enum)

What is an enum?

An enum (enumeration) is a user-defined type consisting of named integer constants. Enums make code more readable by replacing magic numbers with meaningful names.

// Define an enum
enum Day { MON, TUE, WED, THU, FRI, SAT, SUN };
//         0    1    2    3    4    5    6   (default values)

// Declare a variable
enum Day today = WED;
printf("%d\n", today);  // 2

Custom Values

You can assign custom integer values to enum constants. Subsequent constants increment from the last assigned value.

enum Status {
    PENDING  = 0,
    ACTIVE   = 1,
    INACTIVE = 2,
    DELETED  = 99
};

enum Color {
    RED   = 1,
    GREEN = 2,
    BLUE  = 4   // powers of 2 for bit flags
};

typedef enum

Using typedef with enum lets you declare variables without the enum keyword each time.

typedef enum { LOW, MEDIUM, HIGH } Priority;
Priority p = HIGH;  // no need to write 'enum Priority'

Basic enum — Days of Week

#include <stdio.h>

enum Day { MON=1, TUE, WED, THU, FRI, SAT, SUN };

const char* dayName(enum Day d) {
    switch (d) {
        case MON: return "Monday";
        case TUE: return "Tuesday";
        case WED: return "Wednesday";
        case THU: return "Thursday";
        case FRI: return "Friday";
        case SAT: return "Saturday";
        case SUN: return "Sunday";
        default:  return "Unknown";
    }
}

int main() {
    enum Day today = WED;
    printf("Today is %s (value: %d)\n", dayName(today), today);

    // Iterate over all days
    printf("\nAll days:\n");
    for (enum Day d = MON; d <= SUN; d++) {
        printf("  %d: %s\n", d, dayName(d));
    }

    // Check if it's a weekend
    if (today == SAT || today == SUN) {
        printf("\nIt's the weekend!\n");
    } else {
        printf("\nIt's a weekday.\n");
    }

    return 0;
}

/*
Today is Wednesday (value: 3)

All days:
  1: Monday
  2: Tuesday
  ...
  7: Sunday

It's a weekday.
*/

enum with Custom Values, typedef enum and switch

#include <stdio.h>

// typedef enum — no need to write 'enum' when declaring variables
typedef enum {
    HTTP_OK        = 200,
    HTTP_NOT_FOUND = 404,
    HTTP_ERROR     = 500
} HttpStatus;

typedef enum {
    NORTH = 0,
    EAST  = 90,
    SOUTH = 180,
    WEST  = 270
} Direction;

void handleStatus(HttpStatus status) {
    switch (status) {
        case HTTP_OK:
            printf("200 OK — Request successful\n");
            break;
        case HTTP_NOT_FOUND:
            printf("404 Not Found — Resource missing\n");
            break;
        case HTTP_ERROR:
            printf("500 Internal Server Error\n");
            break;
        default:
            printf("Unknown status: %d\n", status);
    }
}

int main() {
    HttpStatus s = HTTP_NOT_FOUND;
    handleStatus(s);
    handleStatus(HTTP_OK);

    Direction dir = EAST;
    printf("\nHeading: %d degrees\n", dir);

    // Enum in array
    Direction path[] = {NORTH, EAST, SOUTH, WEST};
    const char *names[] = {"North", "East", "South", "West"};
    printf("Path: ");
    for (int i = 0; i < 4; i++) {
        printf("%s(%d) ", names[i], path[i]);
    }
    printf("\n");

    return 0;
}

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C Enumerations (enum)

What is an enum?

Custom Values

typedef enum

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