Enums and Typedef in C

Enumeration (enum)

An enum is a user-defined data type consisting of named integer constants. It improves code readability.

Syntax:

enum enum_name { constant1, constant2, constant3, ... };

Example:

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

enum Day today = WED;
printf("Day number: %d\n", today);  /* prints 2 (starts from 0) */

Custom values:

enum Status {
    PENDING = 1,
    ACTIVE = 2,
    INACTIVE = 3
};

Enum in switch:

switch (today) {
    case MON: printf("Monday"); break;
    case FRI: printf("Friday"); break;
    default:  printf("Other day");
}

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Enum vs #define

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typedef

typedef creates an alias for an existing data type. It does not create a new type — just a new name.

Syntax:

typedef existing_type new_name;

Examples:

typedef int Integer;
typedef float Real;
typedef char* String;

Integer x = 10;
Real pi = 3.14;

typedef with struct:

/* Without typedef: */
struct Point { int x, y; };
struct Point p1;

/* With typedef: */
typedef struct {
    int x, y;
} Point;

Point p1;   /* no need to write 'struct' */

typedef with enum:

typedef enum { RED, GREEN, BLUE } Color;

Color c = GREEN;

typedef with pointer:

typedef int* IntPtr;
IntPtr p;   /* same as: int *p; */

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Combined Example

#include <stdio.h>

typedef enum { CIRCLE, RECTANGLE, TRIANGLE } ShapeType;

typedef struct {
    ShapeType type;
    float area;
} Shape;

int main() {
    Shape s;
    s.type = CIRCLE;
    s.area = 3.14 * 5 * 5;
    printf("Area = %.2f\n", s.area);
    return 0;
}