C# in a Nutshell, Second Edition

Variables and Parameters

A variable represents a typed storage location. A variable can be a local variable, parameter, array element, an instance field, or a static field.

All variables have an associated type, which essentially defines the possible values the variable can have and the operations that can be performed on that variable. C# is strongly typed, which means the set of operations that can be performed on a type are enforced at compile time, rather than at runtime. In addition, C# is type-safe, which ensures that a variable can be operated on only via the correct type with the help of runtime checking (except in unsafe blocks; see Section 4.8 in Chapter 4).

Definite Assignment

All variables in C# (except in unsafe contexts) must be assigned a value before they are used. A variable is either explicitly assigned a value or automatically assigned a default value. Automatic assignment occurs for static fields, class instance fields, and array elements not explicitly assigned a value. For example:

using System;
class Test {
  int v;
  // Constructors that initalize an instance of a Test
  public Test( ) {  } // v will be automatically assigned to 0
  public Test(int a) { // explicitly assign v a value
     v = a;
  }
  static void Main( ) {
    Test[ ] tests = new Test [2]; // declare array
    Console.WriteLine(tests[1]); // ok, elements assigned to null
    Test t;
    Console.WriteLine(t); // error, t not assigned before use
  }
}

Default Values

Essentially the default value for all primitive (or atomic) types ...