Variables and Data Types

C# is a statically typed language — every variable has a type known at compile time. This lesson covers the type system, value types, reference types, strings, and nullable types.

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Declaring Variables

Variables in C# are declared with a type followed by a name:

int age = 30;
string name = "Alice";
double price = 19.99;
bool isActive = true;

Type Inference with var

The var keyword lets the compiler infer the type from the assigned value:

var age = 30;          // int
var name = "Alice";    // string
var price = 19.99;     // double
var isActive = true;   // bool

Tip: Use var when the type is obvious from the right-hand side. Use explicit types when clarity is needed.

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Value Types vs Reference Types

Category	Stored In	Assignment	Default	Examples
Value types	Stack	Copies the value	0, false, etc.	int, double, bool, struct, enum
Reference types	Heap	Copies the reference	null	string, class, array, object