C# 3.0 Pocket Reference, 2nd Edition

Type Basics

A type defines the blueprint for a value. A value is a storage location denoted by a variable or a constant. A variable represents a value that can change, whereas a constant represents an invariant. We created a local variable named x in our first program:

	static void Main( )
	{
	  int x = 12 * 30;
	  Console.WriteLine (x);
	}

All values in C# are instances 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 is int.

Predefined Type Examples

Predefined types are types that are specially supported by the compiler. The int type is a predefined primitive type for representing the set of integers that fits into 32 bits of memory, from –2³¹ to 2³¹â€“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 the string type. The string type represents a sequence of characters, such as “.NET” or http://oreilly.com. We can manipulate 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 primitive bool type has exactly two possible values: true and false. The bool type is commonly used to conditionally branch execution flow based with an if statement. For example:

 bool simpleVar = false; if (simpleVar) Console.WriteLine ...