CBasics

C Variables and Data Types

Learn C variables and data types, understand how data is stored in memory, and choose the correct data type for efficient and reliable C programs.

What are Variables in C?Link to this section

Variables are named memory locations used to store data during program execution. Each variable holds a value that can change while the program runs. In C, every variable must be declared with a specific data type before it is used.

Rules for Naming Variables :Link to this section

Variable names in C:
  • Must start with a letter or underscore (_)
  • Can contain letters, digits, and underscores
  • Cannot start with a digit
  • Cannot use C keywords
  • Are case-sensitive

tip

Use meaningful variable names to improve readability.

Declaring Variables in C :Link to this section

A variable declaration specifies the data type and variable name.

Initializing Variables :Link to this section

Initialization assigns an initial value to a variable.

note

Uninitialized variables may contain garbage values.

Basic Data Types in C :Link to this section

C provides several built-in data types to store different kinds of data.
int Used to store integer values.
float Used to store decimal (floating-point) numbers.
double Used to store double-precision floating-point values.
char Used to store a single character.

note

Characters are enclosed in single quotes.

Size of Data Types :Link to this section

The size of data types depends on the system and compiler.

tip

Use sizeof to write portable programs.

Derived Data Types :Link to this section

Derived data types are formed using basic data types. Examples include:
  • Arrays
  • Pointers
  • Structures
  • Unions

note

These will be covered in later topics.

Why Data Types Matter :Link to this section

Choosing the correct data type:
  • Saves memory
  • Improves performance
  • Prevents unexpected behavior

warning

Using the wrong data type can cause overflow and data loss.
Check Your Understanding
Question 1 of 5

What is a variable in C?

Practice Challenges

medium
  • Declare variables to store your age, height, and grade.
  • Initialize variables with different data types and print them.
  • Write a program to display the size of all basic data types.
  • Identify and fix errors in variable declarations.