# Variables in C – How Programs Store Data >

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I recently started teaching a course on C programming and as part of my preparation for class, I usually write out lesson notes that I will be teaching from. I have therefore decided to make these into blog posts so anyone else learning C can also benefit from them. Therefore, this lesson is part of the series I am calling: C Programming for Absolute Beginners. I hope you enjoy it. Ask any questions or leave comments if you need further clarification or want to make a suggestion.

If programs were people, variables would be their memory. Every program needs a way to store information. Numbers. Letters. Results. That’s where variables come in. In this lesson, you’ll learn: * What a variable is * The basic data types in C * How to declare and initialize variables * How to print them Let’s keep it simple. ## 1\. What Is a Variable? A variable is a **named container that stores data in memory**. Think of it like a labeled box. If you write “age” on a box and put the number 20 inside, that box now stores 20. Later, you can open the box and use that number. In C, we create that “box” by declaring a variable. ## 2\. Data Types in C Unlike some other languages, C needs to know **what type of data** you want to store. Why? Because different data types take up different amounts of memory. Here are the most common ones:

Type	Stores	Example
`int`	Whole numbers	10, -5, 200
`float`	Decimal numbers	3.14, 2.5
`double`	Larger decimal numbers	3.141592
`char`	A single character	'A', 'b'

Important: * `int` is for whole numbers. * `float` and `double` are for decimals. * `char` is for a single letter inside single quotes. ## 3\. Declaring a Variable To create a variable in C, you must declare it. The format is: ```plaintext type variable_name; ``` Example: ```c int age; float price; char grade; ``` This tells C: * Create a variable called `age` that stores whole numbers. * Create a variable called `price` that stores decimals. * Create a variable called `grade` that stores one character. Nothing is stored yet. We just created empty containers. ## 4\. Initializing a Variable Initializing means giving the variable a value. Example: ```c int age = 20; float price = 19.99; char grade = 'A'; ``` Here’s what happens: * `age` stores 20 * `price` stores 19.99 * `grade` stores 'A' The `=` symbol is called the assignment operator. It stores the value on the right into the variable on the left. ## 5\. Printing Variables To display output in C, we use `printf`. Example: ```c #include int main() { int age = 20; printf("Age: %d\n", age); return 0; } ``` Let’s break this down: * `#include ` allows us to use `printf`. * `main()` is where the program starts. * `%d` tells C we are printing an integer. * `\n` means move to a new line. Different data types use different format specifiers:

Data Type	Format Specifier
int	%d
float	%f
double	%lf
char	%c

Example with multiple variables: ```c #include int main() { int age = 18; float height = 5.7; char grade = 'B'; printf("Age: %d\n", age); printf("Height: %.1f\n", height); printf("Grade: %c\n", grade); return 0; } ``` `%.1f` means show 1 decimal place. ## 6\. Rules for Naming Variables There are some basic rules: * Must start with a letter or underscore * Cannot start with a number * No spaces allowed * Cannot use C keywords (like `int`, `return`, etc.) Valid names: ```plaintext age studentScore _price ``` Invalid names: ```plaintext 1age student score int ``` ## 7\. Common Beginner Mistakes Here are mistakes to avoid: 1. Forgetting the semicolon `;` 2. Using the wrong format specifier 3. Forgetting single quotes for `char` 4. Mixing up data types (like storing 3.5 in an int) Example mistake: ```c int number = 3.5; // This will cut off the decimal ``` C does not automatically fix these for you. It expects precision. ## 8\. Practice Exercises Try these on your own. 1. Create a variable called `score` and store 85 in it. Print it. 2. Create a float variable called `temperature` and print it with two decimal places. 3. Create a char variable called `initial` and print it. * * * ## Final Thoughts Variables are the foundation of programming. If you understand: * How to declare them * How to assign values * How to print them You’ve taken your first real step in C. In the next lesson, we’ll teach your program how to **make decisions** using `if` statements. And that’s where things start getting interesting.