Enumerated Data Type

Enumeration (enum) in C

📌 Definition

Enumeration (or enum) is a user-defined data type in C.

• Used to assign names to integral constants

• Makes programs easier to read and maintain

• Each symbolic name represents an integer constant

• Declared using the keyword enum

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📌 General Syntax

enum tag_name {member1, member2, member3, ..., memberN} variable1, variable2, ..., variableN;

Notes:

• Either tag_name or variables may be omitted

• Both can also be present

• But at least one must exist

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📌 Default Values of Enum Members

• Members are assigned integer values automatically

• First member → 0

• Second → 1

• Third → 2

• And so on…

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📌 Example Declaration

enum week {Mon, Tue, Wed, Thu, Fri, Sat};
enum week day;

OR

enum week {Mon, Tue, Wed, Thu, Fri, Sat} day;

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📌 Example Program (Default Values)

#include <stdio.h>

enum day {sunday, monday, tuesday, wednesday, thursday, friday, saturday};

int main()
{
    enum day d = thursday;
    printf("The day number stored in d is %d", d);
    return 0;
}

Output

The day number stored in d is 4

(Counting starts from 0)

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📌 Assigning Explicit Values

We can manually assign integer values to enum members.

✔ Example

#include <stdio.h>

enum State {Working = 1, Failed = 0, Freezed = 0};

int main()
{
   printf("%d, %d, %d", Working, Failed, Freezed);
   return 0;
}

Output

1, 0, 0

👉 Two enum names can share the same value.

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📌 Mixed Assignment of Values

• You may assign values to some members

• Remaining members automatically get:

(previous value + 1)

✔ Example

#include <stdio.h>

enum day {sunday = 1, monday, tuesday = 5, wednesday, thursday = 10, friday, saturday};

int main()
{
    printf("%d %d %d %d %d %d %d",
        sunday, monday, tuesday, wednesday, thursday, friday, saturday);
    return 0;
}

Output

1 2 5 6 10 11 12

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📌 Important Rules for Enum

✅ Enum values must be integral constants
✅ Must lie within integer range
✅ Enum constants must be unique within the same scope

❌ Invalid Example

enum state  {working, failed};
enum result {failed, passed};   // Error: duplicate name 'failed'

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📌 Enum vs Macro

We can also define named constants using macros:

#define Working 0
#define Failed 1
#define Freezed 2

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✔ Advantages of enum Over Macros

1. Enums follow scope rules (macros do not)

2. Enum values are automatically assigned

3. Cleaner and easier for related constants

✔ Simpler Using Enum

enum state {Working, Failed, Freezed};