C# 2008 Programmer's Reference

Access modifiers are keywords that you can add to members of a class to restrict their access. Consider the following definition of the Contact class:

public class Contact {
 public const ushort MAX_EMAIL = 5;
 public static int count;
 public int ID;
 public string FirstName;
 public string LastName;
 private string _Email;
}

Unlike the rest of the data members, the _Email data member has been defined with the private keyword. The public keyword indicates that the data member is visible outside the class, while the private keyword indicates that the data member is only visible within the class.

By convention, you can denote a private variable by beginning its name with the underscore (_) character. This is recommended, but not mandatory.

For example, you can access the FirstName data member through an instance of the Contact class:

//---this is OK---
contact1.FirstName = 'Wei-Meng';

But you cannot access the _Email data member outside the class, as the following statement demonstrates:

//---error: _Email is inaccessible---
contact1._Email = '[email protected]';

C# has four access modifiers — private, public, protected, and internal.The last two are discussed with inheritance in the next chapter.

If a data member is declared without the public keyword, its scope (or access) is private by default. So, _Email can also be declared like this:

public class Contact {
 public const ushort MAX_EMAIL = 5;
 public static int count;
 public int ID;
 public string FirstName;
 public string LastName;
 string _Email;
}

Function Members

A function member contains executable code that performs work for the class. The following are examples of function members in C#:

□ Methods

□ Properties

□ Events

□ Indexers

□ User-defined operators

□ Constructors

□ Destructors

Events and indexers are covered in detail in Chapters 7 and 13.

Methods

In C#, every function must be associated with a class. A function defined with a class is known as a method. In C#, a method is defined using the following syntax:

[access_modifiers] return_type method_name(parameters) {
 //---Method body---
}

Here's an example — the ValidateEmail() method defined in the Contact class:

public class Contact {
 public static ushort MAX_EMAIL;
 public int ID;
 public string FirstName;
 public string LastName;
 public string Email;
 public Boolean ValidateEmail() {
  //---implementation here---
  Boolean valid=true;
  return valid;
 }
}

If the method does not return a value, you need to specify the return type as void, as the following PrintName() method shows:

public class Contact {
 public static ushort MAX_EMAIL;
 public int ID;
 public string FirstName;
 public string LastName;
 public string Email;
 public Boolean ValidateEmail() {
  //---implementation here---
  //...
  Boolean valid=true;
  return valid;
 }
 public void PrintName() {
  Console.WriteLine('{0} {1}', this.FirstName, this.LastName);
 }
}

Passing Arguments into Methods

You can pass values into a method using arguments. The words parameter and argument are often used interchangeably, but they mean different things. A parameter is what you use to define a method. An argument is what you actually use to call a method.