Variables & Data Types

Variables are containers for storing data values. C# is a strongly-typed language, which means every variable must have a declared type. Understanding variables and data types is fundamental to C# programming.

Variable Declaration

Variables must be declared before they can be used. C# supports type inference using the var keyword, allowing the compiler to determine the type based on the assigned value.

// Type inference
var name = "John";      // Compiler infers string type
var age = 25;          // Compiler infers int type

// Explicit typing
string firstName = "John";
int userAge = 25;
bool isActive = true;

Common Data Types

Value Types

Value types directly contain their data and are stored on the stack. Each variable has its own copy of the data.

int number = 42;         // Whole numbers
float price = 19.99f;    // Single-precision floating point
double amount = 99.99d;  // Double-precision floating point
decimal precise = 123.456m; // High-precision decimal
bool isValid = true;     // Boolean true/false
char grade = 'A';        // Single character

Reference Types

Reference types store a reference to their data, which is stored on the heap. Multiple variables can reference the same data.

string name = "John Doe";  // String of characters
object obj = new object(); // Base type of all objects
dynamic dynamicVar = 100;  // Type checking at runtime

Constants

Constants are immutable values that cannot be modified after declaration. They must be initialized at declaration time.

const double PI = 3.14159;
const string APP_NAME = "MyApp";
const int MAX_USERS = 100;