📊 Data Types

Primitive and User-Defined in C

🔹 1. What Are Data Types?

Data types define the kind of data a variable can hold. Think of it as labeling boxes: each box (variable) can only store certain kinds of items (data).

🔹 2. Two Main Categories of Data Types in C

Category	Description
Primitive Data Types	Basic built-in types (numbers, characters)
User-Defined Data Types	Custom types created by the programmer

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✨ Primitive Data Types

These are the basic types that come with C by default:

Data Type	Size (Typical)	Description	Example
int	4 bytes	Stores whole numbers (integers)	`int age = 20;`
float	4 bytes	Stores decimal numbers (single precision)	`float pi = 3.14;`
double	8 bytes	Stores decimal numbers (double precision)	`double price = 99.99;`
char	1 byte	Stores a single character	`char grade = 'A';`
void	0 bytes	Represents no value or empty return	`void function();`

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🔍 Example Using Primitive Types:


#include <stdio.h>


int main() {

    int age = 25;

    float temperature = 36.6;

    char initial = 'J';


    printf("Age: %d\n", age);

    printf("Temperature: %.1f\n", temperature);

    printf("Initial: %c\n", initial);


    return 0;

}


Output:

Age: 25

Temperature: 36.6

Initial: J

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🏗️ User-Defined Data Types

Sometimes, you need to create your own data types to organize data better. C allows this with:

struct (structure)
union
enum (enumeration)
typedef (aliasing types)

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1. struct — Structure

Used to group different variables under one name.


struct Person {

    char name[50];

    int age;

    float height;

};

Example:


#include <stdio.h>


struct Person {
    char name[50];
    int age;
    float height;
};


int main() {
    struct Person p1 = {"Alice", 30, 5.6};


    printf("Name: %s\n", p1.name);
    printf("Age: %d\n", p1.age);
    printf("Height: %.1f\n", p1.height);


    return 0;
}

2. union

Like struct but all members share the same memory location.

3. enum — Enumeration

Defines a set of named integer constants.


enum Day { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };

4. typedef

Creates a new name (alias) for an existing type.


typedef unsigned int uint;

uint age = 25;

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🔑 Summary Table

Data Type Category	Purpose	Example
Primitive	Basic data types	int, char, float
User-defined (struct)	Group related variables	`struct Person { ... };`
User-defined (enum)	Named constants	`enum Color {Red, Green};`
User-defined (union)	Memory-efficient data structures	`union Data { ... };`
User-defined (typedef)	Aliasing types	`typedef int MyInt;`

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🚀 Why Does This Matter?

Correct data types help manage memory efficiently.
They allow you to write clearer and more organized code.
User-defined types help model real-world objects.

Frequently Asked Questions – Data Types in C

Q: What is a data type in C?

A: A data type defines the kind of data a variable can store, like integers, floats, characters, or user-defined structures.

Q: What are the two main categories of data types in C?

A: The two main categories are Primitive Data Types and User-Defined Data Types.

Q: What are primitive data types in C?

A: Primitive types are built-in data types like int, float, char, double, and void.

Q: What is the size of an int in C?

A: Typically, an int occupies 4 bytes in most modern systems.

Q: What is the use of the void data type?

A: void represents no value and is often used as a return type for functions that do not return anything.

Q: What is a user-defined data type?

A: User-defined data types are custom types created by the programmer using struct, union, enum, or typedef.

Q: What is a struct in C?

A: A struct is used to group variables of different data types under one name for better data organization.

Q: How is a union different from a struct?

A: In a union, all members share the same memory space, so only one member can be used at a time.

Q: What is an enum in C?

A: An enum defines a set of named integer constants for better code readability.

Q: What is typedef used for?

A: typedef creates an alias for an existing data type, making the code cleaner and easier to maintain.

Q: Can I create my own data types in C?

A: Yes, using struct, union, enum, and typedef, you can define custom data types tailored to your application.

Q: Why use user-defined data types?

A: They help model real-world entities, simplify complex data, and enhance code organization.

Q: What is the default value of an uninitialized variable?

A: C does not initialize variables by default; uninitialized variables contain garbage values.

Q: How do I print values of different data types in C?

A: Use format specifiers like %d for int, %f for float, %c for char, and %s for strings in printf.

Q: Can I nest structs in C?

A: Yes, you can include one struct as a member of another struct for hierarchical data modeling.

Q: What are the advantages of using typedef?

A: It improves readability, reduces complexity, and allows easier modification of type names.

Q: How is memory managed in a union?

A: Memory is allocated based on the largest member, and all members share that memory space.

Q: What are common use cases of enum?

A: enum is commonly used for defining states, days, directions, or modes to improve code clarity.

Q: Can typedef be used with struct?

A: Yes, typedef is often used with struct to simplify declarations. Example: typedef struct { int x; } Point;

Q: Why is understanding data types important?

A: It ensures correct data usage, efficient memory management, and helps avoid logic and runtime errors.

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