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Last updated: Wednesday 08 October 2025 @ 06:59:44

Unions and Structs

  • Create a new folder give it the name unionsandstructs

  • Create a new file called unionsandstructs.c inside that folder

  • modify the contents to look like this:

  • Code

    #include <stdio.h>

int main(){


    return 0;
}

Exercise 1: Structs

Objective: Understand the concept of structs and their usage in C.

  1. Create a C program that defines a Person struct with the following attributes:

    • name (string)
    • age (integer)
    • height (float)

  2. Write a function printPerson that takes a Person struct as a parameter and prints its attributes.

  3. In the main function, create an instance of the Person struct,populate its attributes with your name, age and height, and use the printPerson function to display the details.

  4. Output

  5. Suppressed Code... [30 lines]

     
    #include <stdio.h>

/**
* @struct Person
* @brief Represents information about a person.
*/
struct Person {
    char name[50]; ///< Name of the person.
    int age;       ///< Age of the person.
    float height;  ///< Height of the person.
};

/**
* @brief Prints details of a person.
* @param p The person to be printed.
*/
void printPerson(struct Person p) {
    printf("Name: %s\nAge: %d\nHeight: %.2f\n", p.name, p.age, p.height);
}

/**
* @brief Main function where the program starts execution.
*/
int main() {
    // Create an instance of Person, initialize its attributes, and print details
    struct Person person1 = {"Your Name", 1, 4.0};
    printPerson(person1);

    return 0;
}

Exercise 2: Unions

Objective: Explore the concept of unions and their applications in C.

  1. Create a C program that defines a Data union with the following members:

    • integerData (integer)
    • floatData (float)
    • charData (character)

  2. Write a function printData that takes a Data union as a parameter and prints the value based on the type of data (integer, float, or character).

  3. In the main function, create an instance of the Data union, assign values to different members, and use the printData function to display the values.

  4. Output

  5. Suppressed Code... [33 lines]

     
    #include <stdio.h>

/**
* @union Data
* @brief Represents different types of data (integer, float, char).
*/
union Data {
    int integerData; ///< Integer data.
    float floatData; ///< Float data.
};

/**
* @brief Prints details of data, detecting its type.
* @param d The data to be printed.
*/
void printData(union Data d) {
    printf("Data: ");
    printf("%d (Integer)\n", d.integerData);
    printf("%f (Float)\n", d.floatData);

}

/**
* @brief Main function where the program starts execution.
*/
int main() {
    // Create an instance of Data, assign values, and print details
    union Data data1;
    data1.floatData = 123.45f;
    printData(data1);

    return 0;
}

Exercise 3: Unions Vs Structs

In this exercise we are going to explore the difference between and struct and a union:

  1. Create a struct called Person with the following attributes:

    • name (char size 50)
    • age (integer)
    • height (float)

  2. Create a union called Data with the following attributes:

    • integerData (Int)
    • floatData (float)
    • CharData (char)

  3. In main define a the struct Person as person and the union Data as data

  4. Reproduce the following code to assign person.age and data.integerData and data.floatData:

    Code

    ...
 // Accessing struct members
person.age = 25;
printf("Struct Member - Age: %d\n", person.age);

// Accessing union members
data.integerData = 42;
printf("Union Member - Integer Data: %d\n", data.integerData);

// Modify union member and access another member
data.floatData = 3.14;
printf("Union Member - Float Data: %.2f\n", data.floatData);

  5. Now we are going to compare the size of the struct and the union, reproduce the following after last printf(...) line:

    Code

    ...
// Demonstrate the size difference between struct and union
printf("Size of Struct (Person): %lu bytes\n", sizeof(struct Person));
printf("Size of Union (Data): %lu bytes\n", sizeof(union Data));

  6. Output

  7. Suppressed Code... [49 lines]

     
    #include <stdio.h>

/**
    * @struct Person
    * @brief Represents personal information about a person.
    */
struct Person {
    char name[50]; ///< Name of the person.
    int age;       ///< Age of the person.
    float height;  ///< Height of the person.
};

/**
    * @union Data
    * @brief Represents different types of data (integer, float, char).
    */
union Data {
    int integerData; ///< Integer data.
    float floatData; ///< Float data.
    char charData;   ///< Character data.
};

/**
    * @brief Main function where the program starts execution.
    * @return 0 on successful execution.
    */
int main() {
    // Create an instance of the struct and union
    struct Person person;
    union Data data;

    // Accessing struct members
    person.age = 25;
    printf("Struct Member - Age: %d\n", person.age);

    // Accessing union members
    data.integerData = 42;
    printf("Union Member - Integer Data: %d\n", data.integerData);

    // Modify union member and access another member
    data.floatData = 3.14;
    printf("Union Member - Float Data: %.2f\n", data.floatData);

    // Demonstrate the size difference between struct and union
    printf("Size of Struct (Person): %lu bytes\n", sizeof(struct Person));
    printf("Size of Union (Data): %llu bytes\n", sizeof(union Data));

    return 0;
}

    Info

    • A struct Person is defined with attributes representing personal information.

    • A union Data is defined with three members: integerData, floatData, and charData.

    • In the main function, an instance of both the struct and the union is created.

    • The program demonstrates how to access and modify members of the struct and the union.

    • It prints the size of the struct and union to highlight the memory usage difference.

    • This exercise illustrates the key differences between structs and unions:

    • Struct: Each member has its own memory space, and the size of the struct is the sum of the sizes of its members.

    • Union: All members share the same memory space, and the size of the union is determined by the largest member.

Exercise 4: Combining Structs and Unions

Objective: Understand how structs and unions can be combined for more complex data structures.

  1. Create a new struct named Employee with the following attributes:

    • personalInfo (a Person struct)
    • jobInfo (a Data union representing various job-related information)

  2. Write a function printEmployee that takes an Employee struct as a parameter and prints both personal and job-related information using the previously defined functions (printPerson and printData).

  3. In the main function, create an instance of the Employee struct, populate its attributes, and use the printEmployee function to display the details.

  4. Output

  5. Suppressed Code... [76 lines]

     
    #include <stdio.h>

/**
* @struct Person
* @brief Represents information about a person.
*/
struct Person {
    char name[50]; ///< Name of the person.
    int age;       ///< Age of the person.
    float height;  ///< Height of the person.
};

/**
* @union Data
* @brief Represents different types of data (integer, float, char).
*/
union Data {
    int integerData; ///< Integer data.
    float floatData; ///< Float data.
    char charData;   ///< Character data.
};

/**
* @struct Employee
* @brief Represents information about an employee.
*/
struct Employee {
    struct Person personalInfo; ///< Personal information of the employee.
    union Data jobInfo;         ///< Job-related information of the employee.
};

/**
* @brief Prints details of data, detecting its type.
* @param d The data to be printed.
*/
void printData(union Data d) {
    printf("Data: ");
    if (d.integerData) {
        printf("%d (Integer)\n", d.integerData);
    } else if (d.floatData) {
        printf("%.2f (Float)\n", d.floatData);
    } else {
        printf("%c (Character)\n", d.charData);
    }
}

/**
* @brief Prints details of a person.
* @param p The person to be printed.
*/
void printPerson(struct Person p) {
    printf("Name: %s\nAge: %d\nHeight: %.2f\n", p.name, p.age, p.height);
}

/**
* @brief Prints details of an employee.
* @param e The employee to be printed.
*/
void printEmployee(struct Employee e) {
    printf("Personal Information:\n");
    printPerson(e.personalInfo);
    printf("\nJob Information:\n");
    printData(e.jobInfo);
}

/**
* @brief Main function where the program starts execution.
*/
int main() {
    // Create an instance of Employee, assign values, and print details
    struct Employee employee1 = {{"Alice", 30, 5.5}, {0}};
    employee1.jobInfo.floatData = 75000.50;
    printEmployee(employee1);

    return 0;
}

Additional Challenges:

Challenge 1

Modify the Person struct to include an array of hobbies. Update the relevant functions and demonstrate the changes in the main function.

Challenge 2

Extend the Data union to include an array of integers. Modify the printData function to handle this new data type.

Conclusion:

This lab covers the basics of using structs and unions in C. It helps in understanding how to define, initialise, and manipulate data using these fundamental concepts. Additionally, provides key knowledge and skills for the assignment.