C

Variables and Data Types in C

C 148 views Dec 22, 2025 2 min read

A variable is a named memory location used to store data that can be changed during program execution.

Rules for Naming Variables

  • Must begin with a letter or underscore _

  • Can contain letters, digits, and underscores

  • Cannot start with a digit

  • Cannot use C keywords

  • Case-sensitive

Valid: count, _total, sum1
Invalid: 1num, float, total-value

Declaration of Variables

int a;
float b;
char c;

Initialization of Variables

int a = 10;
float b = 5.5;
char c = 'A';

Types of Variables

  • Local Variables – Declared inside a function

  • Global Variables – Declared outside all functions

  • Static Variables – Retain value between function calls

  • Automatic Variables – Default local variables

Data Types in C

Data types specify the type of data a variable can store.

Classification of Data Types

1. Basic (Primary) Data Types

Data TypeDescription
intInteger values
floatDecimal values
doubleDouble precision decimals
charSingle character

2. Derived Data Types

  • Arrays

  • Pointers

  • Structures

  • Unions

3. Enumeration Data Type

enum day {Mon, Tue, Wed};

4. Void Data Type

  • Represents no value

void display();

Size of Data Types (Typical)

Data TypeSize
char1 byte
int2 or 4 bytes
float4 bytes
double8 bytes

Example Program

#include 

int main() {
    int age = 20;
    float salary = 25000.50;
    char grade = 'A';

    printf("%d %.2f %c", age, salary, grade);
    return 0;
}

Summary

  • Variables store data values

  • Data types define the kind of data

  • C supports multiple data types

  • Proper declaration is mandatory

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