Data Types in C

A variable stores data, but what kind of data can it store?

Can it store numbers?

Can it store decimal values?

Can it store characters?

The answer depends on its data type.

A data type tells the compiler what type of value a variable can hold, how much memory it requires, and what operations can be performed on it.

🎯 Learning Objectives

After completing this lesson, you will be able to:

• Understand what data types are.
• Learn the built-in data types in C.
• Understand memory allocation.
• Learn data type modifiers.
• Use format specifiers correctly.
• Write programs using different data types.

📖 What is a Data Type?

A Data Type specifies the type of data that a variable can store.

For example,

• Age → Integer
• Salary → Decimal
• Grade → Character

Every variable must have a data type.

Example

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int age;

float salary;

char grade;

Why Are Data Types Important?

Data types help the compiler:

• Allocate memory.
• Perform calculations correctly.
• Prevent invalid operations.
• Improve program performance.

Categories of Data Types

C provides four major categories.

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Data Types
│
├── Basic Data Types
│     ├── int
│     ├── char
│     ├── float
│     └── double
│
├── Derived Data Types
│     ├── Arrays
│     ├── Pointers
│     └── Functions
│
├── Enumeration
│
└── Void

For now, we will focus on the basic data types.

Integer (int)

The int data type stores whole numbers.

Examples

• 10
• 25
• -40
• 1000

Example

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#include <stdio.h>

int main()
{
    int age = 20;

    printf("%d", age);

    return 0;
}

Output

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20

Character (char)

The char data type stores a single character.

Example

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#include <stdio.h>

int main()
{
    char grade = 'A';

    printf("%c", grade);

    return 0;
}

Output

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A

Float

The float data type stores decimal numbers.

Example

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#include <stdio.h>

int main()
{
    float cgpa = 8.75;

    printf("%.2f", cgpa);

    return 0;
}

Output

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8.75

Double

The double data type stores large decimal numbers with greater precision.

Example

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#include <stdio.h>

int main()
{
    double pi = 3.1415926535;

    printf("%.10lf", pi);

    return 0;
}

Output

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3.1415926535

Memory Size

Checking Size Using sizeof()

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#include <stdio.h>

int main()
{
    printf("Size of int = %zu\n", sizeof(int));
    printf("Size of char = %zu\n", sizeof(char));
    printf("Size of float = %zu\n", sizeof(float));
    printf("Size of double = %zu\n", sizeof(double));

    return 0;
}

Format Specifiers

Example

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printf("%d", age);

printf("%c", grade);

printf("%f", salary);

printf("%lf", pi);

Data Type Modifiers

Modifiers change the size or range of a data type.

Common modifiers are:

• short
• long
• signed
• unsigned

Example

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short int a;

long int b;

unsigned int c;

long long int d;

Real-Life Example

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#include <stdio.h>

int main()
{
    char platform[] = "KauraX";

    int students = 500;

    float rating = 4.9;

    printf("Platform : %s\n", platform);

    printf("Students : %d\n", students);

    printf("Rating   : %.1f", rating);

    return 0;
}

Output

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Platform : KauraX
Students : 500
Rating   : 4.9

Choosing the Correct Data Type

Common Beginner Mistakes

❌ Using %d for float

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float x = 10.5;

printf("%d", x);

Correct

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printf("%f", x);

❌ Using double with %f

Correct

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printf("%lf", value);

❌ Writing characters using double quotes

Wrong

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char grade = "A";

Correct

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char grade = 'A';

Best Practices

• Use int for whole numbers.
• Use float for decimal values.
• Use double when higher precision is required.
• Use char for single characters.
• Use meaningful variable names.

🧠 Interview Questions

1. What is a data type?
2. Why are data types necessary?
3. Differentiate between float and double.
4. What is the purpose of sizeof()?
5. What are data type modifiers?
6. Explain format specifiers.

✍ Practice Questions

1. Declare variables of different data types.
2. Print the size of each data type.
3. Display your name, age, CGPA, and grade.
4. Write a program using sizeof().
5. Differentiate between float and double.

📚 Lesson Summary

In this lesson, you learned:

• What data types are.
• Basic data types in C.
• Memory size of each data type.
• Format specifiers.
• Data type modifiers.
• Using sizeof().
• Common mistakes and best practices.

Understanding data types helps you write efficient and memory-friendly programs.

🚀 What's Next?

In the next lesson, Constants and Literals, you will learn:

• What constants are.
• Different types of literals.
• The const keyword.
• #define constants.
• Symbolic constants.
• Practical examples.

Happy Coding with KauraX 💙