Union Types:

A union is a user-defined data type similar to a structure, except that all its
members share the same memory location. As a result, a union can store only one
value at a time, corresponding to one of its members.

The size of a union is determined by the size of its largest member. Unions are
used when a variable may hold values of different types at different times, and
memory efficiency is important.

SYNTAX:

union union_name
{
    datatype member1;
    datatype member2;
};

EXAMPLE:

#include <stdio.h>

union Slot {
    int id;
    char grade;
};

int main() {
    union Slot s;

    s.id = 101;
    printf("Value as ID: %d\n", s.id);

    s.grade = 'A'; 
    printf("Value as Grade: %c\n", s.grade);
    return 0;
}