Unions and Enumerations

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A union is a user-defined data type in which all members share the same memory location.

Difference Between Structure and Union

• Structure allocates separate memory for each member

• Union allocates memory equal to the largest member only

Declaration of Union

union union_name {
    data_type member1;
    data_type member2;
};

Example of Union

union data {
    int i;
    float f;
    char c;
};

Declaring Union Variables

union data d;

Accessing Union Members

• Use dot (.) operator

d.i = 10;

Example Program (Union)

#include 

union data {
    int i;
    float f;
    char c;
};

int main() {
    union data d;

    d.i = 10;
    printf("i = %d\n", d.i);

    d.f = 5.5;
    printf("f = %.2f\n", d.f);

    return 0;
}

Applications of Union

• Memory-efficient programming

• Embedded systems

• Handling multiple data types in same memory

Enumerations in C

An enumeration (enum) is a user-defined data type that assigns names to integer constants.

Declaration of Enumeration

enum enum_name {
    constant1,
    constant2,
    constant3
};

Example of Enumeration

enum day {
    MON, TUE, WED, THU, FRI
};

Using Enumeration Variables

enum day d;
d = MON;

Example Program (Enumeration)

#include 

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

int main() {
    enum day d = MON;
    printf("%d", d);
    return 0;
}

Advantages of Enumeration

• Improves code readability

• Reduces use of numeric constants

• Easy maintenance

Summary

• Union shares memory among members

• Structure vs Union differ in memory allocation

• Enumeration represents named integer constants

• Both are user-defined data types