Unions Enumerations and typedef in C Practice Questions with Solutions

Introduction

C provides several useful features for creating and organizing custom data types. A union allows different members to share the same memory location, an enumeration (enum) lets you create meaningful names for integer constants, and typedef gives an existing data type a simpler or more readable name. In this chapter, you will practice all three concepts through simple examples involving students, employees, menus, days, status values, and real-world data. Unions Enumerations and typedef in C practice questions with solutions to help you understand the concepts.

Q1. Create and Display a Union

Problem Statement

Create a union named Data containing an integer, a float, and a character. Store and display an integer value.

C Program

#include <stdio.h>

union Data
{
    int number;
    float price;
    char letter;
};

int main()
{
    union Data data;

    data.number = 100;

    printf("Number = %d", data.number);

    return 0;
}

Sample Output

Number = 100

Explanation

We create a union:

union Data
{
    int number;
    float price;
    char letter;
};

A union can contain multiple members, but all members share the same memory location.

We store:

data.number = 100;

and then display:

printf("%d", data.number);

At this point, number contains the value we stored.

Concepts Covered

union
Union members
Union variable
Accessing union members

Q2. Understand Shared Memory in a Union

Problem Statement

Create a union containing an integer and a float. Store values in both members one after another and observe the result.

C Program

#include <stdio.h>

union Data
{
    int number;
    float value;
};

int main()
{
    union Data data;

    data.number = 100;

    printf("Number = %d\n", data.number);

    data.value = 25.5;

    printf("Value = %.2f\n", data.value);

    printf("Number after storing float = %d", data.number);

    return 0;
}

Sample Output

The final integer value is implementation-dependent because the same memory is being interpreted as different data types. A typical output may look like:

Number = 100
Value = 25.50
Number after storing float = 1103626240

Explanation

Initially:

data.number = 100;

The union’s shared memory contains the representation of 100 as an integer.

Then:

data.value = 25.5;

uses the same memory location to store a floating-point value.

Therefore, you should not expect data.number to still represent the original 100.

The important idea is:

Union
 ┌───────────────┐
 │ Shared Memory │
 └───────────────┘
      ↑     ↑
    int   float

Only the member whose value was most recently stored should normally be read.

Concepts Covered

Shared memory
Union members
Memory representation
Union behavior

Q3. Find the Size of a Union

Problem Statement

Create a union containing an integer, float, and character array. Display the size of the union using sizeof().

C Program

#include <stdio.h>

union Data
{
    int number;
    float price;
    char name[20];
};

int main()
{
    union Data data;

    printf("Size of union = %zu bytes", sizeof(data));

    return 0;
}

Sample Output

The exact size depends on the C implementation, but it will be large enough to hold the largest member, subject to alignment requirements.

For example:

Size of union = 20 bytes

Explanation

The largest member is:

char name[20];

A union must have enough storage for its largest member.

Unlike a structure, union members do not generally have separate storage.

For example:

Structure:
int     → separate memory
float   → separate memory
char[]  → separate memory

Union:
int
float   → same shared memory
char[]

The exact size can also be affected by alignment requirements.

Concepts Covered

sizeof()
Union memory
Largest union member
Memory allocation

Q4. Create an Enum for Days of the Week

Problem Statement

Create an enumeration for the seven days of the week and display the value of a selected day.

C Program

#include <stdio.h>

enum Day
{
    MONDAY,
    TUESDAY,
    WEDNESDAY,
    THURSDAY,
    FRIDAY,
    SATURDAY,
    SUNDAY
};

int main()
{
    enum Day today;

    today = FRIDAY;

    printf("Day value = %d", today);

    return 0;
}

Sample Output

Day value = 4

Explanation

By default, enumeration values start from 0.

Therefore:

MONDAY     → 0
TUESDAY    → 1
WEDNESDAY  → 2
THURSDAY   → 3
FRIDAY     → 4
SATURDAY   → 5
SUNDAY     → 6

When we write:

today = FRIDAY;

the value stored in today is 4.

The names make the program easier to understand than using unexplained numbers such as 4.

Concepts Covered

enum
Enumeration constants
Default enum values
printf()

Q5. Create Custom Values Using `enum`

Problem Statement

Create an enumeration for traffic-light colors with custom integer values and display the selected value.

C Program

#include <stdio.h>

enum TrafficLight
{
    RED = 1,
    YELLOW = 2,
    GREEN = 3
};

int main()
{
    enum TrafficLight signal;

    signal = GREEN;

    printf("Traffic light value = %d", signal);

    return 0;
}

Sample Output

Traffic light value = 3

Explanation

Unlike the previous example, we assign our own values:

RED = 1,
YELLOW = 2,
GREEN = 3

Therefore:

RED    → 1
YELLOW → 2
GREEN  → 3

Now:

signal = GREEN;

stores the enumeration value 3.

Using names such as RED, YELLOW, and GREEN makes the program easier to read.

Concepts Covered

Custom enum values
Enumeration constants
enum variables
Named integer values

Q6. Use `enum` with `switch`

Problem Statement

Create an enumeration for days and use a switch statement to display the selected day.

C Program

#include <stdio.h>

enum Day
{
    MONDAY = 1,
    TUESDAY,
    WEDNESDAY,
    THURSDAY,
    FRIDAY,
    SATURDAY,
    SUNDAY
};

int main()
{
    enum Day day;

    day = FRIDAY;

    switch (day)
    {
        case MONDAY:
            printf("Monday");
            break;

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

        case WEDNESDAY:
            printf("Wednesday");
            break;

        case THURSDAY:
            printf("Thursday");
            break;

        case FRIDAY:
            printf("Friday");
            break;

        case SATURDAY:
            printf("Saturday");
            break;

        case SUNDAY:
            printf("Sunday");
            break;
    }

    return 0;
}

Sample Output

Friday

Explanation

The enumeration gives meaningful names to integer values:

MONDAY    → 1
TUESDAY   → 2
WEDNESDAY → 3
...

We set:

day = FRIDAY;

Then switch checks the value of day.

The matching case is:

case FRIDAY:
    printf("Friday");
    break;

This combination is useful for menus, states, categories, and other fixed choices.

Concepts Covered

enum
switch
Enumeration constants
break

Q7. Create a `typedef` for an Integer

Problem Statement

Use typedef to create a new name called Age for the int data type.

C Program

#include <stdio.h>

typedef int Age;

int main()
{
    Age studentAge = 15;

    printf("Student Age = %d", studentAge);

    return 0;
}

Sample Output

Student Age = 15

Explanation

This statement:

typedef int Age;

creates Age as an alias for int.

Now instead of:

int studentAge;

we can write:

Age studentAge;

typedef does not create a completely new integer type. It creates another name for an existing type.

Concepts Covered

typedef
Type aliases
Integer variables
Custom type names

Q8. Use `typedef` with a Structure

Problem Statement

Create a student structure using typedef so that the struct keyword is not required when declaring variables.

C Program

#include <stdio.h>

typedef struct
{
    int roll;
    char name[50];
    float marks;
} Student;

int main()
{
    Student student = {101, "Rahul", 88.5};

    printf("Roll = %d\n", student.roll);
    printf("Name = %s\n", student.name);
    printf("Marks = %.2f", student.marks);

    return 0;
}

Sample Output

Roll = 101
Name = Rahul
Marks = 88.50

Explanation

Without typedef, we might write:

struct Student student;

With typedef:

Student student;

The definition:

typedef struct
{
    int roll;
    char name[50];
    float marks;
} Student;

creates Student as an alias for that structure type.

This can make structure declarations shorter and easier to read.

Concepts Covered

typedef
Structures
Type aliases
Structure initialization

Q9. Use `typedef` with a Structure Pointer

Problem Statement

Create a student structure using typedef and use a pointer to modify the student’s marks.

C Program

#include <stdio.h>

typedef struct
{
    int roll;
    char name[50];
    float marks;
} Student;

int main()
{
    Student student = {101, "Aman", 75.5};

    Student *ptr = &student;

    printf("Before Update = %.2f\n", ptr->marks);

    ptr->marks = 90.0;

    printf("After Update = %.2f", ptr->marks);

    return 0;
}

Sample Output

Before Update = 75.50
After Update = 90.00

Explanation

Because Student is created using typedef, we can write:

Student student;

and:

Student *ptr;

The pointer stores the address of the structure:

Student *ptr = &student;

The marks are accessed using:

ptr->marks

and modified using:

ptr->marks = 90.0;

Concepts Covered

typedef
Structure pointer
-> operator
Modifying structure data

Q10. Combine `union`, `enum`, and `typedef`

Problem Statement

Create a simple product record using typedef, an enum for product type, and a union for product-specific information.

C Program

#include <stdio.h>

typedef enum
{
    BOOK = 1,
    ELECTRONIC = 2
} ProductType;

typedef union
{
    int pages;
    float warranty;
} ProductInfo;

typedef struct
{
    char name[50];
    ProductType type;
    ProductInfo info;
} Product;

int main()
{
    Product product;

    printf("Enter product name: ");
    scanf("%49s", product.name);

    product.type = BOOK;
    product.info.pages = 250;

    printf("\nProduct Details\n");
    printf("Name = %s\n", product.name);

    if (product.type == BOOK)
    {
        printf("Type = Book\n");
        printf("Pages = %d", product.info.pages);
    }
    else if (product.type == ELECTRONIC)
    {
        printf("Type = Electronic\n");
        printf("Warranty = %.1f years", product.info.warranty);
    }

    return 0;
}

Sample Output

Enter product name: CProgramming

Product Details
Name = CProgramming
Type = Book
Pages = 250

Explanation

This program combines all three concepts.

First:

typedef enum
{
    BOOK = 1,
    ELECTRONIC = 2
} ProductType;

creates a convenient name for the enumeration.

typedef union
{
    int pages;
    float warranty;
} ProductInfo;

creates a union for product-specific information.

Finally:

typedef struct
{
    char name[50];
    ProductType type;
    ProductInfo info;
} Product;

creates the complete product structure.

The union is useful here because a book needs:

pages

while an electronic product might need:

warranty

Both pieces of information do not need to be stored at the same time.

Concepts Covered

typedef
enum
union
Structures
Nested custom types
Structure members
switch/conditional logic

Key Takeaways

A union allows multiple members to share the same memory.
A union is useful when only one of several possible data values needs to be stored at a time.
A union’s size is sufficient for its largest member, subject to alignment requirements.
An enum gives meaningful names to integer constants.
Enumeration values start at 0 by default unless explicitly assigned.
You can assign custom values to enumeration constants.
enum is useful for fixed choices such as days, colors, status values, and menu options.
typedef creates an alias for an existing data type.
typedef is commonly used with structures and enumerations.
typedef can make structure declarations shorter and easier to read.
union, enum, and typedef can be combined in larger C programs.
These concepts become especially useful when designing organized and memory-conscious C programs.

FAQs

1. What is a union in C?

A union is a user-defined data type whose members share the same memory location. Normally, only one member’s stored value should be treated as active at a time.

2. What is the difference between a structure and a union?

A structure gives its members separate storage, allowing all members to hold values simultaneously. A union shares storage among its members, so storing one member can overwrite the representation of another.

3. What is an enum in C?

An enum is an enumeration type used to create named integer constants.

For example:

enum Color
{
    RED,
    GREEN,
    BLUE
};

4. What is the default value of the first enum constant?

The first enumeration constant has the value 0 by default.

For example:

enum Day
{
    MONDAY,
    TUESDAY,
    WEDNESDAY
};

has:

MONDAY    = 0
TUESDAY   = 1
WEDNESDAY = 2

5. What is `typedef` in C?

typedef creates an alias for an existing type.

For example:

typedef int Age;

allows:

Age age = 15;

instead of:

int age = 15;

6. Can `typedef` be used with structures?

Yes. A common pattern is:

typedef struct
{
    int id;
    char name[50];
} Student;

Then you can declare:

Student student;

7. Can `enum`, `union`, and `typedef` be used together?

Yes. They can be combined to create organized data types for larger programs. For example, typedef can give a simple name to an enum or union, while a structure can contain those types as members.

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Rishabh Kumar

Introduction

Q1. Create and Display a Union

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q2. Understand Shared Memory in a Union

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q3. Find the Size of a Union

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q4. Create an Enum for Days of the Week

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q5. Create Custom Values Using enum

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q6. Use enum with switch

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q7. Create a typedef for an Integer

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q8. Use typedef with a Structure

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q9. Use typedef with a Structure Pointer

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q10. Combine union, enum, and typedef

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Key Takeaways

FAQs

1. What is a union in C?

2. What is the difference between a structure and a union?

3. What is an enum in C?

4. What is the default value of the first enum constant?

5. What is typedef in C?

6. Can typedef be used with structures?

7. Can enum, union, and typedef be used together?

Related Posts

Q5. Create Custom Values Using `enum`

Q6. Use `enum` with `switch`

Q7. Create a `typedef` for an Integer

Q8. Use `typedef` with a Structure

Q9. Use `typedef` with a Structure Pointer

Q10. Combine `union`, `enum`, and `typedef`

5. What is `typedef` in C?

6. Can `typedef` be used with structures?

7. Can `enum`, `union`, and `typedef` be used together?