C Structure vs Union

C Structure vs Union – Key Differences

In C programming, structures and unions are user-defined data types that group different variables under one name. While they seem similar, they differ in how they handle memory and store values.

📦 Structure

A structure allocates separate memory for each member. All members can hold values independently.

📝 Example: Structure

#include <stdio.h>

struct MyStruct {
    int i;
    float f;
    char ch;
};

int main() {
    struct MyStruct s = {10, 3.14, 'A'};

    printf("Integer: %d\n", s.i);
    printf("Float: %.2f\n", s.f);
    printf("Character: %c\n", s.ch);

    return 0;
}
  

💡 Union

A union allocates one shared memory for all members. Only one member can contain a valid value at any time, as all members overlap in memory.

📝 Example: Union

#include <stdio.h>

union MyUnion {
    int i;
    float f;
    char ch;
};

int main() {
    union MyUnion u;

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

    u.f = 3.14;
    printf("Float: %.2f\n", u.f);

    u.ch = 'A';
    printf("Character: %c\n", u.ch);

    // Notice how previous values get overwritten
    printf("After char, integer: %d\n", u.i);

    return 0;
}
  

🔍 Structure vs Union Comparison

🎯 Practice Tip

Use structures when you need all data available at once. Use unions when you need to save memory and only one variable is active at a time. Try modifying the examples to see memory behavior in action!