Data Types in C

Why Do We Need Data Types?

• To tell the compiler how much memory to reserve.
• To define the type of value stored (int, float, char, etc.).
• To prevent invalid operations.
• To improve program efficiency.

Categories of Data Types in C

1. Basic Data Types  
2. Derived Data Types  
3. User-defined Data Types

1. Basic Data Types

Integer (int)

Stores whole numbers without decimals.

int age = 25;

Float

Stores decimal numbers (single precision).

float price = 99.75;

Double

Stores large decimal numbers (double precision).

double distance = 12345.6789;

Character (char)

Stores a single character.

char grade = 'A';

2. Derived Data Types

• Arrays
• Pointers
• Functions

int marks[5];     // array  
int *ptr;         // pointer  
void test();      // function

3. User-defined Data Types

• struct (Structure)
• union (Union)
• enum (Enumeration)
• typedef (Alias)

struct Student {
    int roll;
    char name[20];
};

Size of Data Types

char      → 1 byte  
int       → 4 bytes  
float     → 4 bytes  
double    → 8 bytes  
long int  → 8 bytes  
short int → 2 bytes  

Sizes may vary depending on the compiler.

Signed & Unsigned Types

Signed → can store + and - values
Unsigned → only + values, larger range

signed int x = -10;
unsigned int y = 50;

Format Specifiers

%d → int  
%f → float  
%c → char  
%lf → double  
%u → unsigned int  
%ld → long int  

Practical Example

#include <stdio.h>

int main() {

    int age = 25;
    float salary = 45000.50;
    double distance = 98765.432;
    char grade = 'A';

    printf("Age: %d\n", age);
    printf("Salary: %.2f\n", salary);
    printf("Distance: %.3lf\n", distance);
    printf("Grade: %c\n", grade);

    return 0;
}

Practical Example 2 – Size of Data Types

#include <stdio.h>

int main() {

    printf("Size of int: %lu bytes\n", sizeof(int));
    printf("Size of float: %lu bytes\n", sizeof(float));
    printf("Size of double: %lu bytes\n", sizeof(double));
    printf("Size of char: %lu byte\n", sizeof(char));

    return 0;
}

Practical Example 3 – Signed vs Unsigned

#include <stdio.h>

int main() {

    signed int a = -20;
    unsigned int b = 20;

    printf("Signed: %d\n", a);
    printf("Unsigned: %u\n", b);

    return 0;
}

Practical Example 4 – Unsigned Overflow Behavior

#include <stdio.h>

int main() {

    unsigned int x = 0;
    x = x - 1;   // causes wrap-around

    printf("Unsigned Overflow Result: %u\n", x);

    return 0;
}

Practical Example 5 – Range Difference

#include <stdio.h>

int main() {

    signed int s = 32767;        // maximum for 16-bit (example)
    unsigned int u = 65535;      // maximum for 16-bit unsigned

    printf("Signed Max Example: %d\n", s);
    printf("Unsigned Max Example: %u\n", u);

    return 0;
}

Practical Example 6 – Negative Values in Unsigned

#include <stdio.h>

int main() {

    unsigned int num = -10;   // negative assigned to unsigned

    printf("Storing -10 in unsigned gives: %u\n", num);

    return 0;
}

Practice Questions

1. What are data types? Why are they necessary?
2. Differentiate between int, float, and double.
3. What is the size of basic data types?
4. Write a program to demonstrate signed and unsigned types.
5. Write 5 differences between structure and union.

Practice Task