A union is a user-defined data type that allows you to store different data types in the same memory location. Unlike structures, which allocate memory for each member separately, unions allocate enough memory to hold the largest member. This means that all members share the same memory space.

Examples :

Program.c

#include <stdio.h> // Define a union named MyUnion union MyUnion { int intValue; float floatValue; char stringValue[20]; }; int main() { // Declare a variable of type union MyUnion union MyUnion myData; // Assign values to different members of the union myData.intValue = 42; printf("Value of intValue: %d\n", myData.intValue); myData.floatValue = 3.14f; printf("Value of floatValue: %f\n", myData.floatValue); // Assign a string to the char array member snprintf(myData.stringValue, sizeof(myData.stringValue), "Hello, Union!"); printf("Value of stringValue: %s\n", myData.stringValue); // Print the sizes of the union and its members printf("Size of MyUnion: %u bytes\n", sizeof(union MyUnion)); printf("Size of intValue: %u bytes\n", sizeof(myData.intValue)); printf("Size of floatValue: %u bytes\n", sizeof(myData.floatValue)); printf("Size of stringValue: %u bytes\n", sizeof(myData.stringValue)); return 0; }

Output:

        Value of intValue: 42
        Value of floatValue: 3.140000
        Value of stringValue: Hello, Union!
        Size of MyUnion: 20 bytes
        Size of intValue: 4 bytes
        Size of floatValue: 4 bytes
        Size of stringValue: 20 bytes