Variable Naming Rules

Part of the Fundamentals section of Coddy's C journey — lesson 12 of 63.

In C, variable naming rules are important to follow for creating valid and readable code. Here are the key rules:

Variable names can contain letters (a-z, A-Z), digits (0-9), and underscores (_).

They must begin with a letter or underscore, not a digit.

C is case-sensitive, so myVariable and myvariable are different.

Keywords (like int, float, return) cannot be used as variable names.

No spaces or special characters (except underscore) are allowed.

Good practices for naming variables include:

Use descriptive names that indicate the variable's purpose.

Use camelCase or snake_case for multi-word names.

Keep names concise but meaningful.

int age;        // Good: starts with a letter
float _price;   // Good: starts with an underscore

Use only letters, numbers, and underscores:

int item123;    // Good: contains letters and numbers
float cost_per_unit;  // Good: uses underscore

Variable names are case-sensitive:

int value;
int Value;    // This is a different variable than "value"

Avoid using C keywords:

int if;        // Wrong: "if" is a keyword
int total;     // Good: "total" is not a keyword

Challenge

Easy

Write a program that declares and initializes two variables with valid names according to C naming rules.
The first variable should be an integer named "userAge" set to 25. The second variable should be a float named "item_price" set to 9.99.
Then print both variables using printf in the following format:

User age: 25
Item price: 9.99

Cheat sheet

C variable naming rules:

Can contain letters (a-z, A-Z), digits (0-9), and underscores (_)
Must begin with a letter or underscore, not a digit
Case-sensitive: myVariable and myvariable are different
Cannot use C keywords (like int, float, return)
No spaces or special characters except underscore

Good naming practices:

Use descriptive names
Use camelCase or snake_case for multi-word names
Keep names concise but meaningful

Valid variable names:

int age;        // Good: starts with a letter
float _price;   // Good: starts with an underscore
int item123;    // Good: contains letters and numbers
float cost_per_unit;  // Good: uses underscore

Case sensitivity example:

int value;
int Value;    // Different variable than "value"

Avoid C keywords:

int if;        // Wrong: "if" is a keyword
int total;     // Good: "total" is not a keyword

Try it yourself

#include <stdio.h>

int main() {
    // Declare and initialize two variables with valid names
    // Print both variables
    
    return 0;
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction

C Language Hello World!Comments Basic Program Structure

4Control Flow

If Statement If - Else Else-If Switch Case Ternary Conditional Operator Recap Challenge Nested If - Else

7Functions

Declare a Function Return Types Parameters Recap Challenge #1 Recursion Basics Function Prototypes Recap Challenge #2