A variable is a named location in the computer's memory used to store data. Think of it as a labeled container where you can put information, retrieve it later, and change it as needed while the program is running.

Variables are the fundamental building blocks for storing and manipulating data in any C program.

Declaring and Initializing Variables

Before you can use a variable, you must declare it. A declaration tells the compiler the variable's name and the type of data it will hold.

Syntax for Declaration

data_type variable_name;

·         data_type: Specifies the type of data the variable can store (e.g., int for integers, float for floating-point numbers, char for characters).

·         variable_name: The unique name you give to the variable.

Example Declaration:

C

int studentId;    // Declares a variable to hold an integer

float temperature;  // Declares a variable to hold a floating-point number

char grade;         // Declares a variable to hold a single character

Syntax for Initialization

Initialization means assigning an initial value to a variable at the time of its declaration. It's a good practice to initialize variables to avoid them holding unpredictable "garbage" values.

data_type variable_name = value;

Example Initialization:

C

int studentId = 101;

float temperature = 98.6;

char grade = 'A';

Rules for Naming Variables (Identifiers)

The name you give to a variable (also known as an identifier) must follow these rules:

·         It can only contain letters (a-z, A-Z), digits (0-9), and the underscore (_) character.

·         It must begin with a letter or an underscore. It cannot start with a digit.

·         It cannot be a keyword. For example, you cannot name a variable int or for.

·         C is case-sensitive, which means age and Age are two different variables.

Example of Variables in a Program

This program demonstrates how to declare, initialize, use, and modify variables of different types.

C

#include <stdio.h>

int main() {

    // 1. Declare and initialize variables of different types

    int age = 25;

    float weight = 65.5;

    char initial = 'R';

    // 2. Print the initial values of the variables

    // %d, %f, and %c are format specifiers for int, float, and char

    printf("Initial age: %d\n", age);

    printf("Initial weight: %f kg\n", weight);

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

    // 3. Modify the value of the 'age' variable

    age = age + 1; // Increment the age by 1

    // 4. Print the updated value

    printf("Age next year will be: %d\n", age);

    return 0;

}

Code Breakdown:

1.   We declare three variables: age as an integer, weight as a floating-point number, and initial as a character, assigning them initial values.

2.   The printf() function is used to display the stored values. We use format specifiers (%d, %f, %c) to tell printf what type of data to expect.

3.   The value of the age variable is changed. This demonstrates that variables are "variable" and their contents can be modified.

4.   The new value of age is printed to show the change.