Chapter Three

1
Chapter Three

• Using Methods

2
Objectives

• Learn how to write methods with no arguments and
  no return value
• Learn about implementation hiding and how to use
  multiple files
• Learn how to write methods that require a single
  argument
• Learn how to write methods that require multiple
  arguments
• Learn how to write methods that return a value

3
Objective

• Learn how to use reference and output parameters
  with methods
• Learn how to overload methods
• Learn how to avoid ambiguous methods

4
Writing Methods with No Arguments and No Return
Value

• A method is a series of statements that carry out
  a task
• A method can be invoked or called by other
  methods
• Method names are always followed by a set of
  parentheses
• Programmers can create custom methods
• Example
• Console.WriteLine(HELLO WORLD)

5
Writing Methods with No Arguments and No Return
Value

• In C, a method must include
• A method declaration
• An opening curly brace
• A method body
• A closing brace

6
Writing Methods with No Arguments and No Return
Value

• The optional access modifiers for a method
  include public, protected internal, protected,
  internal, and private
• If an access modifier for a method is not
  declared, the method becomes private by default
• The static keyword indicates that a method can be
  called without referring to an object
• Every method has a return type (int is by default)

7
Writing Methods with No Arguments and No Return
Value

• The optional access modifiers
• Public Unlimited access
• protected internal Access to program or type
  derived from class
• Protected Access to containing class or type
  derived from class
• Internal Access to containing program
• Private access to the contained type.

8
Writing Methods with No Arguments and No Return
Value

• This is an example of a method calling another
  method

9
Hiding Implementation by Using Multiple Files

• An important principle of object-oriented
  programming is the notion of implementation
  hiding
• The users of methods should only be aware of the
  interface
• The following implementation, with two newline
  escape sequences, could have been used instead of
  the previous codeneither implementation effects
  the user

10
Hiding Implementation by Using Multiple Files

• Two different implementations of the
  WelcomeMessage() method

11
Hiding Implementation by Using Multiple Files

• A multifile assembly is a program that is
  composed of many different files and classes
• A netmodule file is a file that contains modules
  to be used as part of another program
• Compiling multifile assemblies and netmodules
  requires a slightly different command
• csc /tmodule LogoNamespace.cs
• csc DemoLogo2.cs /addmoduleLogoNameSpace.netmodul
  e

12
Writing Methods That Require a Single Argument

• Arguments or parameters are used to communicate
  and send additional information to methods
• The following items are included in the method
  declaration parentheses when declaring a method
  that can receive an argument
• The type of the argument
• A local name for the argument

13
Writing Methods That Require a Single Argument

• The identifier saleAmount is simply the name the
  value goes by while it is used in the method,
  regardless of the name the value goes by in the
  calling program

14
Writing Methods That Require a Single Argument

• A formal parameter is a parameter in the method
  declaration
• An actual parameter refers to an argument within
  a method call

15
Writing Methods That Require a Single Argument

• Complete program using the ComputeSevenPercentSale
  sTax() method

16
Writing Methods That Require a Single Argument

• Output of UseSevenPercentSalesTax program

17
Writing Methods That Require Multiple Arguments

• You can pass multiple arguments to a method by
  listing the arguments within the call to the
  method and separating them with commas
• You can write a method to take any number of
  arguments in any order

18
Writing Methods That Return Values

• The return type for a method can be any type used
  in the C programming language
• A method can also return nothing, in which case
  the return type is void
• A methods return type is also known as a
  methods type

19
Writing Methods That Return Values

• The return type in the above example is double
• The return statement causes the value stored in
  gross to be sent back to any method that calls
  the CalcPay() method

20
Writing Methods That Return Values

• Program using the CalcPay() method

21
Using ref and out Parameters Within Methods

• In C, you can write methods with four kinds of
  formal parameters listed within the parentheses
  in the method header
• Value parameters
• Reference parameters
• Output parameters
• Parameter arrays

22
Using ref and out Parameters Within Methods

• When you use a value parameter in a method
  header, you indicate the parameters type and
  name, and the method receives a copy of the value
  passed to it

23
Using ref and out Parameters Within Methods

• Both the reference and output parameters have
  memory addresses that are passed to a method,
  allowing it to alter the original variables
• When you use a reference parameter to a method,
  the parameter must be assigned a value before you
  use it in the method call
• When you use an output parameter, it does not
  contain an original value

24
Using ref and out Parameters Within Methods

• Both reference and output parameters act as
  aliases, or other names, for the same memory
  location
• The keyword ref is used to indicate a reference
  parameter
• The keyword out is used to indicate an output
  parameter

25
Using ref and out Parameters Within Methods

• Program calling method with a reference parameter

26
Using ref and out Parameters Within Methods

• In the preceding code
• The modifier ref precedes the variable in both
  the method call and the method header
• The passed and received variables occupy the same
  memory location
• The passed variable was assigned a value

27
Using ref and out Parameters Within Methods

• Unlike the reference parameter, the output
  parameter does not need a value assigned to it
  (before it is used in a method call)
• The output parameter is convenient when the
  passed variable doesnt have a value yet
• The output parameter gets its value from the
  method, and these values persist back to the
  calling program

28
Overloading Methods

• Overloading involves using one term to indicate
  diverse meanings
• When you overload a C method, you write multiple
  methods with a shared name
• The compiler understands the meaning based on the
  arguments you use with the method

29
Avoiding Ambiguous Methods

• By overloading methods, you run the risk of
  creating an ambiguous situation
• An ambiguous situation is one in which the
  compiler cannot determine which method to use
• The compiler usually distinguishes between
  overloaded methods by the argument lists, but
  this is NOT always possible

30
Avoiding Ambiguous Methods

• If only one method exists, there is no chance of
  an ambiguous situation
• This code would work fine even if your arguments
  were both of type int

31
Avoiding Ambiguous Methods

• What happens when another version of the same
  method is added?
• An ambiguous situation does not exist because the
  compiler can determine the appropriate method

32
Avoiding Ambiguous Methods

• A more complicated and potentially ambiguous
  situation arises when the compiler cannot
  determine which of several versions of a method
  to use

33
Avoiding Ambiguous Methods

• An ambiguous situation arises because there is no
  exact match for the method call
• An overloaded method is not ambiguous on its
  ownit become ambiguous only if you create an
  ambiguous situation

34
Chapter Summary

• A method is a series of reusable statements that
  carry out a task
• Invoking programs must know the interface to
  methods but need not understand the hidden
  implementation
• Methods receive data in the form of parameters or
  arguments
• You can pass multiple arguments to a method by
  listing the arguments within the call to the
  method and separating them with commas

35
Chapter Summary

• The return type for a method can be any type in
  the C programming language
• In C, you can write methods with four kinds of
  formal parameters listed within the parentheses
  in the method header
• Overloading a method involves writing multiple
  methods with the same name, but with different
  arguments
• The compiler determines which of several versions
  of a method to call based on argument lists