Variables in C: A Beginner's Guide to Storing and Using Data

Day-5

1. What Is a Variable in C?

A variable is a named storage space in the computer's memory where you can store data. Think of it as a labeled box where you can keep your data safe and access it when needed.

Real-World Example:
Imagine you are organizing a bookshelf. Each book has a title, and you can find it easily by its name. In programming, a variable works the same way; it holds a piece of data you can reference by its name.

2. Why Do We Use Variables?

Variables make your program flexible. You can store information, change it when needed, and use it throughout your code. This makes your code easier to read and manage.

3. How to Declare and Initialize Variables

Declaration: You tell the program you want to create a variable and specify what type of data it will hold.
Initialization: You give the variable an initial value.

Syntax:

data_type variable_name = value; 
 or 
data_type variable_name; // First Declare variable name 
variable_name = 20; // Next initialize value 

Example:

int age = 25;     // Declares an int variable named age and sets it to 25
float temperature = 36.5; // Declares a float variable named temperature and sets it to 36.5
char initial = 'A'; // Declares a char variable named initial and sets it to 'A'
    

4. Value Types and How to Print Them

In C, we use format specifiers to print the values of variables.

Examples:

• %d for integers (int)
• %f for floating-point numbers (float)
• %c for characters (char)

Example Code:

#include <stdio.h>

int main() {
    // Declaring and initializing variables
    int age = 25;
    float temperature = 36.5;
    char initial = 'A';

    // Printing the values using format specifiers 
    printf("Age: %d\n", age); // Prints an integer value  ( \n ) is called an escape sequence, change its position to the beginning of the next line on the screen.
    printf("Temperature: %.1f\n", temperature); // Prints a float value with 1 decimal place
    printf("Initial: %c\n", initial); // Prints a character value

    return 0;
}
    

Explanation:
The printf function is used to display values on the screen.
The format specifiers (%d, %f, %c) tell the program what type of data you are printing.
%.1f is used for float to show one decimal place.

Important Points About Variables

Naming Rules:

• Start with a letter (a-z, A-Z) or an underscore (_).
• Can include letters, numbers (0-9), and underscores but cannot start with a number.
• Cannot use C keywords (e.g., int, return, char).

Best Practices:

• Use descriptive names for clarity (e.g., totalScore instead of ts).
• Keep your variable names consistent (e.g., snake_case or camelCase).

5. Memory Storage of Variables

How Variables Are Stored:

• Variables in C are stored in memory, but how they are stored depends on the type and scope of the variable.
• Local variables are stored in the stack, which is a part of memory used for short-term storage.
• Global variables are stored in a different part of memory called the data segment , which is accessible by all functions.

7. Do’s and Don’ts for Variables

Do:

• Initialize variables before using them to avoid errors.
• Use comments to explain what each variable represents, especially if it’s not obvious.
• Choose meaningful names for better code readability.

Don’t:

• Use reserved keywords as variable names.
• Leave variables uninitialized (undefined behavior may occur).
• Use overly short or unclear variable names.

Recap:

• Variables are named containers that hold data in memory.
• Always choose the appropriate data type and give meaningful names to your variables.
• Variables are stored in memory differently depending on whether they are local or global.
• Follow good practices to make your code easy to read and maintain.