C# 4.0 Pocket Reference, 3rd Edition

Type Basics

A type defines the blueprint for a value. A value is a storage location denoted by a variable (if it can change) or a constant (if it cannot). We created a local variable named x in our first program.

All values in C# are an instance of a specific type. The meaning of a value, and the set of possible values a variable can have, is determined by its type. The type of x in our example program is int.

Predefined Type Examples

Predefined types (also called built-in types) are types that are specially supported by the compiler. The int type is a predefined type for representing the set of integers that fit into 32 bits of memory, from ‒2³¹ to 2³¹‒1. We can perform functions such as arithmetic with instances of the int type as follows:

int x = 12 * 30;

Another predefined C# type is string. The string type represents a sequence of characters, such as “.NET” or “http://oreilly.com”. We can work with strings by calling functions on them as follows:

string message = "Hello world";
string upperMessage = message.ToUpper();
Console.WriteLine (upperMessage);      // HELLO WORLD

int x = 2007;
message = message + x.ToString();
Console.WriteLine (message);         // Hello world2007

The predefined bool type has exactly two possible values: true and false. The bool type is commonly used to conditionally branch execution flow with an if statement. For example:

bool simpleVar = false; if (simpleVar) Console.WriteLine ("This will not print"); int x = 5000; bool lessThanAMile = x < 5280; if (lessThanAMile) Console.WriteLine ...