Value Types
Value types store their data directly. The most common ones are: int (32-bit integer), long (64-bit integer), double (64-bit floating point), float (32-bit floating point), decimal (128-bit high-precision), bool (true/false), and char (single Unicode character).
int age = 30;
long population = 8_100_000_000L; // underscores aid readability
double pi = 3.14159265358979;
float temp = 36.6f; // 'f' suffix for float
decimal price = 19.99m; // 'm' suffix for decimal
bool isOnSale = true;
char grade = 'A';
Console.WriteLine($"Age: {age}, Price: {price:C2}");Reference Types
Reference types store a reference (pointer) to their data on the heap. The most important reference types are string, arrays, and objects (instances of classes). A reference type variable can be null, meaning it refers to nothing.
Type Inference with var
The var keyword tells the compiler to infer the type from the right-hand side of the assignment. The type is still static—it cannot change at runtime. Use var when the type is obvious from context; use explicit types when clarity matters.
var message = "Hello"; // inferred as string var count = 42; // inferred as int var items = new List();// inferred as List // NOT allowed — var requires an initialiser // var x; ← compile error
Nullable Types
Append ? to any value type to make it nullable: int? can hold an integer or null. Use the null-coalescing operator ?? to provide a default value, and the null-conditional operator ?. to safely call members.
int? score = null; Console.WriteLine(score ?? -1); // prints -1 score = 95; Console.WriteLine(score ?? -1); // prints 95 string? name = null; int len = name?.Length ?? 0; // safe — len is 0
Type Conversion
An implicit conversion happens automatically when no data is lost (e.g. int → long). An explicit cast is required when data might be lost (e.g. double → int). The Convert class and Parse/TryParse methods handle string-to-type conversions safely.
int i = 100;
long l = i; // implicit — safe
double d = 9.99;
int truncated = (int)d; // explicit cast — truncates to 9
string input = "123";
int parsed = int.Parse(input); // throws if invalid
bool ok = int.TryParse("abc", out int val); // ok = false, val = 0