Enums in C Programming

tutorial 21 July 2026 20 min read

Enums in C Programming – Complete Guide with MCQs for CDAC C-CAT

Enums are one of the most frequently tested topics in the CDAC C-CAT C Programming section. Although they appear simple, many questions combine enums with memory allocation, implicit values, typedef, switch statements, integer conversions, and compiler behavior.

This guide covers everything you need for the exam and technical interviews.

What is an Enum?

An enumeration (enum) is a user-defined data type that consists of a set of named integer constants.

Instead of writing numeric values directly in the code, enums make programs easier to read and maintain.

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

Here,

MON = 0
TUE = 1
WED = 2
THU = 3
FRI = 4
SAT = 5
SUN = 6

By default, numbering starts from 0.

Why Use Enums?

Instead of

int day = 3;

write

enum Day day = THU;

Advantages:

  • Improves readability
  • Eliminates magic numbers
  • Makes switch statements cleaner
  • Easier maintenance
  • Better self-documentation

Basic Syntax

enum Color
{
    RED,
    GREEN,
    BLUE
};

enum Color c = GREEN;

Memory Representation

Many students think enums store strings.

They do not.

Memory stores only an integer.

enum Color c = BLUE;

Memory

+--------+
|   2    |
+--------+

The identifier BLUE simply represents the integer 2.

Default Values

enum Number
{
    A,
    B,
    C,
    D
};

Values become

A = 0
B = 1
C = 2
D = 3

Assigning Explicit Values

enum Status
{
    FAIL = 0,
    PASS = 1
};

Output

FAIL = 0
PASS = 1

Mixed Explicit and Implicit Values

enum Number
{
    A = 5,
    B,
    C,
    D = 20,
    E,
    F
};

Values

A = 5
B = 6
C = 7
D = 20
E = 21
F = 22

Rule:

Every implicit value becomes

Previous value + 1

Duplicate Values are Allowed

enum Test
{
    A = 1,
    B = 1,
    C = 1
};

This is perfectly valid.

Output

A = 1
B = 1
C = 1

Names must be unique.

Values need not be.

Negative Values

enum Test
{
    A = -5,
    B,
    C
};

Values

A = -5
B = -4
C = -3

Enum Variables

enum Color
{
    RED,
    GREEN,
    BLUE
};

int main()
{
    enum Color c = GREEN;

    printf("%d", c);
}

Output

1

Enum is Basically an Integer

enum Color
{
    RED,
    GREEN,
    BLUE
};

printf("%d", RED);

Output

0

Printing Enum

enum Day
{
    MON,
    TUE,
    WED
};

printf("%d", WED);

Output

2

Enums do not automatically print names.

Enum to Integer Conversion

enum Color c = BLUE;

int x = c;

printf("%d", x);

Output

2

Integer to Enum

enum Color c;

c = 10;

printf("%d", c);

Output

10

The compiler usually allows this.

The value need not belong to the enum.

Size of Enum

enum Test
{
    A,
    B,
    C
};

printf("%zu", sizeof(enum Test));

Typical Output

4

Most compilers use the same size as int.

typedef with Enum

Instead of

enum Color c;

write

typedef enum
{
    RED,
    GREEN,
    BLUE
} Color;

Color c = GREEN;

Much cleaner.

Enum in Switch Statement

enum Day
{
    MON,
    TUE,
    WED
};

enum Day d = TUE;

switch(d)
{
case MON:
    printf("Monday");
    break;

case TUE:
    printf("Tuesday");
    break;

case WED:
    printf("Wednesday");
    break;
}

Output

Tuesday

Anonymous Enum

enum
{
    RED,
    GREEN,
    BLUE
};

printf("%d", GREEN);

Output

1

No enum type name is created.

Enum Constants are Compile-Time Constants

enum
{
    SIZE = 100
};

int arr[SIZE];

Perfectly valid.

Common Mistakes

Mistake 1

enum Color;

Color c;

Wrong.

Need

enum Color c;

unless typedef is used.

Mistake 2

printf("%s", RED);

Wrong.

Enums are integers.

Mistake 3

Thinking enums store strings.

Wrong.

Only integers are stored.

Frequently Asked Interview Questions

Can enum values repeat?

Yes.

Can enum start from any number?

Yes.

Can enum contain negative numbers?

Yes.

Are enums stored as strings?

No.

What is the default first value?

0

Can enum be used inside switch?

Yes.

What is the size of enum?

Usually the size of an int.

Can enum contain floating point values?

No.

Can we increment enum values automatically?

Yes.

enum
{
A = 100,
B,
C
};

becomes

100
101
102

CDAC C-CAT MCQs

MCQ 1

enum Test
{
A,
B,
C
};

printf("%d", B);

A. 0

B. 1

C. 2

D. Error

Answer: B

MCQ 2

enum Test
{
A=5,
B,
C
};

printf("%d %d", B, C);

A. 5 6

B. 6 7

C. 7 8

D. Error

Answer: B

MCQ 3

enum Test
{
A=-2,
B,
C
};

printf("%d", C);

A. -1

B. 0

C. 1

D. 2

Answer: B

MCQ 4

enum Test
{
A=2,
B=2,
C=2
};

printf("%d", C);

A. Error

B. 2

C. 3

D. Undefined

Answer: B

MCQ 5

enum Test
{
A,
B
};

enum Test x;

x = 100;

printf("%d", x);

A. Error

B. 100

C. Undefined

D. Compiler dependent

Answer: B

MCQ 6

typedef enum
{
RED,
GREEN,
BLUE
} Color;

Color c = BLUE;

printf("%d", c);

A. 1

B. 2

C. 3

D. Error

Answer: B

MCQ 7

enum Test
{
A=10,
B,
C=50,
D
};

printf("%d %d", B, D);

A. 10 50

B. 11 51

C. 11 50

D. 12 51

Answer: B

MCQ 8

enum Test
{
A,
B,
C
};

printf("%zu", sizeof(enum Test));

Typical Output

A. 1

B. 2

C. 4

D. 8

Answer: C (Most compilers)

Key Takeaways

  • An enum is a collection of named integer constants.
  • Default values start at 0.
  • Explicit values override automatic numbering.
  • Following values increment automatically.
  • Duplicate values are allowed.
  • Enums are stored as integers, not strings.
  • sizeof(enum) is typically the same as sizeof(int).
  • typedef enum removes the need to write the enum keyword repeatedly.
  • Enums improve readability, maintainability, and are widely used in switch statements, embedded systems, operating systems, and application development.

Next Topics

To strengthen your C programming for CDAC C-CAT, continue with:

  • Storage Classes in C
  • Typedef in C
  • Structures and Unions
  • Bit Fields
  • Arrays and Pointers
  • Dynamic Memory Allocation
  • Preprocessor Directives
  • Function Pointers
  • Command Line Arguments
  • File Handling