1. Chapter 6 - Methods
Outline Introduction Program Modules in C# Math Class Methods Methods Method Definitions Argument Promotion C# Namespaces Value Types and Reference Types Passing Arguments: Call-by-Value vs. Call-by-Reference Random-Number Generation Example: Game of Chance Duration of Identifiers Scope Rules Recursion Example Using Recursion: The Fibonacci Series Recursion vs. Iteration Method Overloading

2. The .NET Framework Class Library (FCL)
6.2 Program Modules in C#
Modules
Class
Method
Enables use of classes or methods without knowledge of how they work, just what they should do
The .NET Framework Class Library (FCL)
Helps to increase reusability
Console
MessageBox

3. 6.2 Program Modules in C# boss worker1 worker2 worker3 worker4 worker5
Fig. 6.1 Hierarchical boss method/worker method relationship.

4. 6.3 Math Class Methods The Math class
Allows the user to perform common math calculations
Using methods
ClassName.MethodName( argument1, arument2, … )
List of methods are in Fig. 6.2
Constants
Math.PI = …
Math.E = …

5. 6.3 Math Class Methods

6. 6.4 Methods Variables Reasons for using
Declared in a method = local variables
Declared outside a method = global variables
Only the method that defines them know they exist
Send parameters to communicate with other methods
Reasons for using
Divide and conquer
Reusability
Use classes and methods as building blocks for new ones
Cut down on repetition
Methods can be called from anywhere in a program

7. Writing a custom method
6.5 Method Definitions
Writing a custom method
Header
ReturnType Properties Name( Param1, Param2, … )
Body
Contains the code of what the method does
Contains the return value if necessary
For uses call elsewhere in program
Pass parameters if needed
All methods must be defined inside of a class

8. Start of class SquareInteger. It implements System.Windows.Forms.Form
1 // Fig. 6.3: SquareInt.cs 2 // A programmer-defined Square method using System; // includes basic data types 5 using System.Drawing; // for graphics capabilities 6 using System.Collections; // for complex data structures 7 using System.ComponentModel; // controls component behavior 8 using System.Windows.Forms; // for GUI development 9 using System.Data; // for reading outside data // form used to display results of squaring 10 numbers 12 public class SquareIntegers : System.Windows.Forms.Form 13 { private System.ComponentModel.Container components = null; // label containing results private System.Windows.Forms.Label outputLabel; public SquareIntegers() { // Required for Windows Form Designer support InitializeComponent(); int result; // store result of call to method Square 25
Subtract.cs
Start of class SquareInteger. It implements System.Windows.Forms.Form
Start of the SquareIntegers method
This is the method’s variables. They can only be used within the method.

9. The main body of the SquareIntegers method Subtract.cs
// loop 10 times
for ( int counter = 1; counter <= 10; counter++ ) {
// calculate square of counter and store in result
result = Square( counter ); 31
// append result to output string
outputLabel.Text += "The square of " + counter +
" is " + result + "\n"; } 36
} // end SquareIntegers 38
// Clean up any resources being used.
protected override void Dispose( bool disposing ) {
// Visual Studio .NET-generated code for method Dispose } 44
// Required method for Designer support
private void InitializeComponent() {
// Visual Studio .NET generated code
// for method InitializeComponent } 51
The main body of the SquareIntegers method
Subtract.cs
A call to the Square method. The counter variable is passed to it for use. The return value is stored in result

10. Subtract.cs Program Output
// The main entry point for the application.
[STAThread]
static void Main() {
Application.Run( new SquareIntegers() ); } 58
// Square method definition
int Square( int y ) {
return y * y; // return square of y 63
} // end method Square 65
66 } // end of class SquareIntegers
Subtract.cs Program Output
The Square method. Receives one integer and returns an integer
The method returns the passed variable multiplied by itself

11. The program gets three values from the user
1 // Fig. 6.4: MaximumValue.cs
2 // Finding the maximum of three doubles. 3
4 using System; 5
6 class MaximumValue
7 {
// main entry point for application
static void Main( string[] args ) {
// obtain user input and convert to double
Console.Write( "Enter first floating-point value: " );
double number1 = Double.Parse( Console.ReadLine() ); 14
Console.Write( "Enter second floating-point value: " );
double number2 = Double.Parse( Console.ReadLine() ); 17
Console.Write( "Enter third floating-point value: " );
double number3 = Double.Parse( Console.ReadLine() ); 20
// call method Maximum to determine largest value
double max = Maximum( number1, number2, number3 ); 23
// display maximum value
Console.WriteLine("\nmaximum is: " + max ); 26
} // end method Main
MaximumValue.cs
The program gets three values from the user
The three values are then passed to the Maximum method for use

12. MaximumValue.cs Program Output28
// Maximum method uses method Math.Max to help determine
// the maximum value
static double Maximum( double x, double y, double z ) {
return Math.Max( x, Math.Max( y, z ) ); 34
} // end method Maximum 36
37 } // end class MaximumValue
MaximumValue.cs Program Output
The Maximum method receives 3 variables and returns the largest one
The use of Math.Max uses the Max method in class Math. The dot operator is used to call it.
Enter first floating-point value: 37.3
Enter second floating-point value: 99.32
Enter third floating-point value:
maximum is: 99.32

13. 6.6 Argument Promotion Implicit Conversion Explicit Conversion
Object is converted to a needed type implicitly
Only done if complier knows no data will be lost
Explicit Conversion
Object is manually converted
Required if there could be a loss of data
Widening
Make an object that of a derived class and more complex
Narrowing
Make an object that of a base class and cause some data loss

14. 6.6 Argument Promotion

15. 6.7 C# Namespaces Namespace A group of classes and their methods
FCL is composed of namespaces
Namespaces are stored in .dll files called assemblies
A list of the FLC namespaces are in Fig. 6.6
.NET Framework, class library for info on all namespaces
Included in a program with the using keyword

16. 6.7 C# Namespaces

17. 6.8 Value Types and Reference Types
Contains data of the specified type
Programmer created
structs
enumerations (Chapter 8)
Reference types
Contain an address to a spot in memory where the data is
Programmer create
Classes (Chapter 8)
Interfaces (Chapter 8)
Delegates (Chapter 9)
All values are 32bit allowing cross-platform use

18. 6.9 Passing Arguments: Call-By-Value vs. Call-By-Reference
Passing by value
Send a method a copy of the object
When returned are always returned by value
Set by value by default
Passing by reference
Send a method the actual reference point
Causes the variable to be changed throughout the program
When returned are always returned by reference
The ref keyword specifies by reference
The out keyword means a called method will initialize it

19. Since the methods are void they do not need a return value.
1 // Fig. 6.8: RefOutTest.cs
2 // Demonstrating ref and out parameters. 3
4 using System;
5 using System.Windows.Forms; 6
7 class RefOutTest
8 {
// x is passed as a ref int (original value will change)
static void SquareRef( ref int x ) {
x = x * x; } 14
// original value can be changed and initialized
static void SquareOut( out int x ) {
x = 6;
x = x * x; } 21
// x is passed by value (original value not changed)
static void Square( int x ) {
x = x * x; } 27
static void Main( string[] args ) {
// create a new integer value, set it to 5
int y = 5;
int z; // declare z, but do not initialize it 33
RefOutTest.cs
When passing a value by reference the value will be altered in the rest of the program as well
Since the methods are void they do not need a return value.
Since x is passed as out the variable can then be initialed in the method
Since not specified, this value is defaulted to being passed by value. The value of x will not be changed elsewhere in the program because a duplicate of the variable is created.

20. The calling of the SquareRef and SquareOut methods
// display original values of y and z
string output1 = "The value of y begins as "
y + ", z begins uninitialized.\n\n\n"; 37
// values of y and z are passed by value
RefOutTest.SquareRef( ref y );
RefOutTest.SquareOut( out z ); 41
// display values of y and z after modified by methods
// SquareRef and SquareOut
string output2 = "After calling SquareRef with y as an " +
"argument and SquareOut with z as an argument,\n" +
"the values of y and z are:\n\n" +
"y: " + y + "\nz: " + z + "\n\n\n"; 48
// values of y and z are passed by value
RefOutTest.Square( y );
RefOutTest.Square( z ); 52
// values of y and z will be same as before because Square
// did not modify variables directly
string output3 = "After calling Square on both x and y, " +
"the values of y and z are:\n\n" +
"y: " + y + "\nz: " + z + "\n\n"; 58
MessageBox.Show( output1 + output2 + output3,
"Using ref and out Parameters", MessageBoxButtons.OK,
MessageBoxIcon.Information ); 62
} // end method Main 64
65 } // end class RefOutTest
RefOutTest.cs
The calling of the SquareRef and SquareOut methods
The calling of the SquareRef and SquareOut methods by passing the variables by value

21. RefOutTest.cs Program Output

22. 6.10 Random Number Generation
Class Random
Within namespace System
Truly random
The numbers are generated using an equations with a seed
The seed is usually the exact time of day
randomObject.Next()
Returns a number from 0 to Int32.MaxValue
Int32.MaxValue = 2,147,483,647
randomObject.Next( x )
Returns a value from 0 up to but not including x
randomObject.Next( x, y )
Returns a number between x and up to but not including y

23. Creates a new Random object
1 // Fig. 6.9: RandomInt.cs
2 // Random integers. 3
4 using System;
5 using System.Windows.Forms; 6
7 // calculates and displays 20 random integers
8 class RandomInt
9 {
// main entry point for application
static void Main( string[] args ) {
int value;
string output = ""; 15
Random randomInteger = new Random(); 17
// loop 20 times
for ( int i = 1; i <= 20; i++ ) {
// pick random integer between 1 and 6
value = randomInteger.Next( 1, 7 );
output += value + " "; // append value to output 24
// if counter divisible by 5, append newline
if ( i % 5 == 0 )
output += "\n"; 28
} // end for structure 30
RandomInt.cs
Creates a new Random object
Will set value to a random number from1 up to but not including 7
Format the output to only have 5 numbers per line

24. RandomInt.cs Program Output
MessageBox.Show( output, "20 Random Numbers from 1 to 6",
MessageBoxButtons.OK, MessageBoxIcon.Information ); 33
} // end Main 35
36 } // end class RandomInt
Display the output in a message box
RandomInt.cs Program Output

25. RollDie.cs 1 // Fig. 6.10: RollDie.cs 2 // Rolling 12 dice. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data;
10 using System.IO; // enables reading data from files 11
12 // form simulates the rolling of 12 dice,
13 // and displays them
14 public class RollDie : System.Windows.Forms.Form
15 {
private System.ComponentModel.Container components = null; 17
private System.Windows.Forms.Button rollButton; 19
private System.Windows.Forms.Label dieLabel2;
private System.Windows.Forms.Label dieLabel1;
private System.Windows.Forms.Label dieLabel3;
private System.Windows.Forms.Label dieLabel4; 24
private Random randomNumber = new Random(); 26
public RollDie() {
InitializeComponent(); } 31
// Visual Studio .NET-generated code 33
RollDie.cs

26. Pass the labels to be assigned data
// method called when rollButton clicked,
// passes labels to another method
protected void rollButton_Click(
object sender, System.EventArgs e ) {
// pass the labels to a method that will
// randomly assign a face to each die
DisplayDie( dieLabel1 );
DisplayDie( dieLabel2 );
DisplayDie( dieLabel3 );
DisplayDie( dieLabel4 ); 45
} // end rollButton_Click 47
// determines image to be displayed by current die
public void DisplayDie( Label dieLabel ) {
int face = 1 + randomNumber.Next( 6 ); 52
// displays image specified by filename
dieLabel.Image = Image.FromFile(
Directory.GetCurrentDirectory() +
"\\images\\die" + face +".gif" ); } 58
// main entry point for application
[STAThread]
static void Main() {
Application.Run( new RollDie() ); } 65
66 } // end class RollDie
RollDie.cs
Pass the labels to be assigned data
Will return a random integer from 0 up to 6

27. RollDie.cs Program Output

28. RollDie2.cs 1 // Fig. 6.11: RollDie2.cs
2 // Rolling 12 dice with frequency chart. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data;
10 using System.IO; 11
12 // displays the different dice and frequency information
13 public class RollDie2 : System.Windows.Forms.Form
14 {
private System.ComponentModel.Container components = null; 16
private System.Windows.Forms.Button rollButton; 18
private System.Windows.Forms.RichTextBox displayTextBox; 20
private System.Windows.Forms.Label dieLabel1;
private System.Windows.Forms.Label dieLabel2;
private System.Windows.Forms.Label dieLabel3;
private System.Windows.Forms.Label dieLabel4;
private System.Windows.Forms.Label dieLabel5;
private System.Windows.Forms.Label dieLabel6;
private System.Windows.Forms.Label dieLabel7;
private System.Windows.Forms.Label dieLabel8;
private System.Windows.Forms.Label dieLabel9;
private System.Windows.Forms.Label dieLabel10;
private System.Windows.Forms.Label dieLabel11;
private System.Windows.Forms.Label dieLabel12; 33
private Random randomNumber = new Random();
RollDie2.cs

29. Sets all of the variables to 035
private int ones, twos, threes, fours, fives, sixes; 37
public RollDie2() {
InitializeComponent();
ones = twos = threes = fours = fives = sixes = 0; } 43
// Visual Studio .NET-generated code 45
// simulates roll by calling DisplayDie for
// each label and displaying the results
protected void rollButton_Click(
object sender, System.EventArgs e ) {
// pass the labels to a method that will
// randomly assign a face to each die
DisplayDie( dieLabel1 );
DisplayDie( dieLabel2 );
DisplayDie( dieLabel3 );
DisplayDie( dieLabel4 );
DisplayDie( dieLabel5 );
DisplayDie( dieLabel6 );
DisplayDie( dieLabel7 );
DisplayDie( dieLabel8 );
DisplayDie( dieLabel9 );
DisplayDie( dieLabel10 );
DisplayDie( dieLabel11 );
DisplayDie( dieLabel12 ); 65
double total = ones + twos + threes + fours + fives + sixes; 67
RollDie2.cs
Sets all of the variables to 0
Pass the label to be assigned a random number

30. Displays to the user the amount of times each dice number has shown up
// display the current frequency values
displayTextBox.Text = "Face\t\tFrequency\tPercent\n1\t\t" +
ones + "\t\t" +
String.Format( "{0:F2}", ones / total * 100 ) +
"%\n2\t\t" + twos + "\t\t" +
String.Format( "{0:F2}", twos / total * 100 ) +
"%\n3\t\t" + threes + "\t\t" +
String.Format( "{0:F2}", threes / total * 100 ) +
"%\n4\t\t" + fours + "\t\t" +
String.Format( "{0:F2}", fours / total * 100 ) +
"%\n5\t\t" + fives + "\t\t" +
String.Format( "{0:F2}", fives / total * 100 ) +
"%\n6\t\t" + sixes + "\t\t" +
String.Format( "{0:F2}", sixes / total * 100 ) + "%"; 82
} // end rollButton_Click 84
// display the current die, and modify frequency values
public void DisplayDie( Label dieLabel ) {
int face = 1 + randomNumber.Next( 6 ); 89
dieLabel.Image = Image.FromFile(
Directory.GetCurrentDirectory() +
"\\images\\die" + face + ".gif" ); 93
Displays to the user the amount of times each dice number has shown up
RollDie2.cs
Assign a random face to the label based on the number generated

31. A switch statement is used to keep track of number of each die rolled
// add one to frequency of current face
switch ( face ) {
case 1: ones++;
break; 99
case 2: twos++;
break;
102
case 3: threes++;
break;
105
case 4: fours++;
break;
108
case 5: fives++;
break;
111
case 6: sixes++;
break;
114
} // end switch
116
} // end DisplayDie
118
// The main entry point for the application.
[STAThread]
static void Main() {
Application.Run( new RollDie2() ); }
125
126 } // end of class RollDie2
A switch statement is used to keep track of number of each die rolled
RollDie2.cs

32. RollDie2.cs Program Output

33. 6.11 Example: Game of Chance
GUI controls
A GroupBox
Holds other controls
Manages/organizes them
A PictureBox
Used to display a picture on the form

34. CrapsGame.cs 1 // Fig. 6.12: CrapsGame.cs 2 // Craps Game 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data;
10 using System.IO; 11
12 public class CrapsGame : System.Windows.Forms.Form
13 {
private System.ComponentModel.Container components = null; 15
private System.Windows.Forms.PictureBox imgPointDie2;
private System.Windows.Forms.PictureBox imgDie2;
private System.Windows.Forms.PictureBox imgDie1; 19
private System.Windows.Forms.Label lblStatus; 21
private System.Windows.Forms.Button rollButton;
private System.Windows.Forms.Button playButton; 24
private System.Windows.Forms.PictureBox imgPointDie1; 26
private System.Windows.Forms.GroupBox fraPoint; 28
// declare other variables
int myPoint;
int myDie1;
int myDie2; 33
CrapsGame.cs

35. Creates an enumeration of the constant values in craps CrapsGame.cs
public enum DiceNames {
SNAKE_EYES = 2,
TREY = 3,
CRAPS = 7,
YO_LEVEN = 11,
BOX_CARS = 12, } 42
public CrapsGame() {
InitializeComponent(); } 47
// Visual Studio .NET-generated code 49
// simulate next roll and result of that roll
protected void rollButton_Click(
object sender, System.EventArgs e ) {
int sum;
sum = rollDice(); 56
if ( sum == myPoint ) {
lblStatus.Text = "You Win!!!";
rollButton.Enabled = false;
playButton.Enabled = true; }
Creates an enumeration of the constant values in craps
CrapsGame.cs
When the second rolled sum equals the first rolled sum the player wins

36. If the second roll equals CRAPS (7), then the player loses
else
if ( sum == ( int )DiceNames.CRAPS ) {
lblStatus.Text = "Sorry. You lose.";
rollButton.Enabled = false;
playButton.Enabled = true; } 70
} // end rollButton_Click 72
// simulate first roll and result of that roll
protected void playButton_Click(
object sender, System.EventArgs e ) {
int sum;
myPoint = 0;
fraPoint.Text = "Point";
lblStatus.Text = "";
imgPointDie1.Image = null;
imgPointDie2.Image = null; 83
sum = rollDice(); 85
CrapsGame.cs
If the second roll equals CRAPS (7), then the player loses

37. If on the first roll the players gets a 7 or an 11 they win
switch ( sum ) {
case ( int )DiceNames.CRAPS:
case ( int )DiceNames.YO_LEVEN:
rollButton.Enabled = false; // disable Roll button
lblStatus.Text = "You Win!!!";
break;
case ( int )DiceNames.SNAKE_EYES:
case ( int )DiceNames.TREY:
case ( int )DiceNames.BOX_CARS:
rollButton.Enabled = false;
lblStatus.Text = "Sorry. You lose.";
break;
default:
myPoint = sum;
fraPoint.Text = "Point is " + sum;
lblStatus.Text = "Roll Again";
displayDie( imgPointDie1, myDie1 );
displayDie( imgPointDie2, myDie2 );
playButton.Enabled = false;
rollButton.Enabled = true;
break;
108
} // end switch
110
} // end playButton_Click
112
private void displayDie( PictureBox imgDie, int face ) {
imgDie.Image = Image.FromFile(
Directory.GetCurrentDirectory() +
"\\images\\die" + face + ".gif" ); }
119
CrapsGame.cs
If on the first roll the players gets a 7 or an 11 they win
If the first roll is a 2, 3 or 12, the player loses.
Any other number allows the player to roll again

38. Generates two random numbers, one for each die
// simulates the rolling of two dice
private int rollDice() {
int die1, die2, dieSum;
Random randomNumber = new Random();
125
die1 = randomNumber.Next( 1, 7 );
die2 = randomNumber.Next( 1, 7 );
128
displayDie( imgDie1, die1 );
displayDie( imgDie2, die2 );
131
myDie1 = die1;
myDie2 = die2;
dieSum = die1 + die2;
return dieSum;
136
} // end rollDice
138
// main entry point for application
[STAThread]
static void Main() {
Application.Run(new CrapsGame()); }
145
146 } // end of class CrapsGame
CrapsGame.cs
Generates two random numbers, one for each die

39. CrapsGame.cs Program Output

40. 6.12 Duration of Identifiers
The amount of time an identifier exist in memory
Scope
The section of a program in which the object can be referenced
Local variables
Created when declared
Destroyed when the block exits
Not initialized
Most variables are set to 0
All bool variables are set to false
All reference variables are set to null

41. 6.13 Scope Rules
Scope
Portion of a program in which a variable can be accessed
Class scope
From when created in class
Until end of class (})
Global to all methods in that class
Direct modification
Repeated names causes previous to be hidden until scope ends
Block scope
From when created
Until end of block (})
Only used within that block
Must be passed and modified indirectly
Cannot repeat variable names

42. Will output the value of 5
1 // Fig. 6.13: Scoping.cs
2 // A Scoping example. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data; 10
11 public class Scoping : System.Windows.Forms.Form
12 {
private System.ComponentModel.Container components = null;
private System.Windows.Forms.Label outputLabel; 15
public int x = 1; 17
public Scoping() {
InitializeComponent(); 21
int x = 5; // variable local to constructor 23
outputLabel.Text = outputLabel.Text +
"local x in method Scoping is " + x; 26
MethodA(); // MethodA has automatic local x;
MethodB(); // MethodB uses instance variable x
MethodA(); // MethodA creates new automatic local x
MethodB(); // instance variable x retains its value 31
outputLabel.Text = outputLabel.Text +
"\n\nlocal x in method Scoping is " + x; }
Scoping.cs
This variable has class scope and can be used by any method in the class
This variable is local only to Scoping. It hides the value of the global variable
Will output the value of 5
Remains 5 despite changes to global version of x

43. Uses a new x variable that hides the value of the global x35
// Visual Studio .NET-generated code 37
public void MethodA() {
int x = 25; // initialized each time a is called 41
outputLabel.Text = outputLabel.Text +
"\n\nlocal x in MethodA is " + x +
" after entering MethodA"; x;
outputLabel.Text = outputLabel.Text +
"\nlocal x in MethodA is " + x +
" before exiting MethodA"; } 50
public void MethodB() {
outputLabel.Text = outputLabel.Text +
"\n\ninstance variable x is " + x +
" on entering MethodB";
x *= 10;
outputLabel.Text = outputLabel.Text +
"\ninstance varable x is " + x +
" on exiting MethodB"; } 61
// main entry point for application
[STAThread]
static void Main() {
Application.Run( new Scoping() ); } 68
69 } // end of class Scoping
Scoping.cs
Uses a new x variable that hides the value of the global x
Uses the global version of x (1)
Will permanently change the value of x globally

44. Scoping.cs Program Output

45. 6.14 Recursion Recursive methods Methods that call themselves
Directly
Indirectly
Call others methods which call it
Continually breaks problem down to simpler forms
Must converge in order to end recursion
Each method call remains open (unfinished)
Finishes each call and then finishes itself

46. 6.14 Recursion (a) Procession of recursive calls. 5! 5 * 4! 4 * 3!
3 * 2!
2 * 1! 1
(b) Values returned from each recursive call.
Final value = 120
5! = 5 * 24 = 120 is returned
4! = 4 * 6 = 24 is returned
2! = 2 * 1 = 2 is returned
3! = 3 * 2 = 6 is returned
1 returned
Fig Recursive evaluation of 5!.

47. FactorialTest.cs 1 // Fig. 6.15: FactorialTest.cs
2 // Recursive Factorial method. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data; 10
11 public class FactorialTest : System.Windows.Forms.Form
12 {
private System.ComponentModel.Container components = null; 14
private System.Windows.Forms.Label outputLabel; 16
public FactorialTest() {
InitializeComponent(); 20
for ( long i = 0; i <= 10; i++ )
outputLabel.Text += i + "! = " +
Factorial( i ) + "\n"; } 25
FactorialTest.cs

48. FactorialTest.cs Program Output
// Visual Studio .NET-generated code 27
public long Factorial( long number ) {
if ( number <= 1 ) // base case
return 1; 32
else
return number * Factorial( number - 1 ); } 36
[STAThread]
static void Main() {
Application.Run( new FactorialTest()); } 42
43 } // end of class FactorialTest
The Factorial method calls itself (recursion)
FactorialTest.cs Program Output
The recursion ends when the value is less than or equal to 1

49. 6.15 Example Using Recursion: The Fibonacci Sequence
F(n) = F(n - 1) + F(n - 2)
Recursion is used to evaluate F(n)
Complexity theory
How hard computers need to work to perform algorithms

50. FibonacciTest.cs 1 // Fig. 6.16: FibonacciTest.cs
2 // Recursive fibonacci method. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data; 10
11 public class FibonacciTest : System.Windows.Forms.Form
12 {
private System.ComponentModel.Container components = null; 14
private System.Windows.Forms.Button calculateButton; 16
private System.Windows.Forms.TextBox inputTextBox; 18
private System.Windows.Forms.Label displayLabel;
private System.Windows.Forms.Label promptLabel; 21
public FibonacciTest() {
InitializeComponent(); } 26
// Visual Studio .NET-generated code 28
FibonacciTest.cs

51. The number uses the Fibonacci method to get its result
// call Fibonacci and display results
protected void calculateButton_Click(
object sender, System.EventArgs e ) {
string numberString = ( inputTextBox.Text );
int number = System.Convert.ToInt32( numberString );
int fibonacciNumber = Fibonacci( number );
displayLabel.Text = "Fibonacci Value is " + fibonacciNumber; } 38
// calculates Fibonacci number
public int Fibonacci( int number ) {
if ( number == 0 || number == 1 )
return number;
else
return Fibonacci( number - 1 ) + Fibonacci( number - 2 ); } 47
[STAThread]
static void Main() {
Application.Run( new FibonacciTest() ); } 53
54 } // end of class FibonacciTest
FibonacciTest.cs
The number uses the Fibonacci method to get its result
The recursion ends when the number is 0 or 1
Calls itself twice, to get the result of the the two previous numbers

52. FibonacciTest.cs Program Output

53. 6.15 Example Using Recursion: The Fibonacci Sequence
return 1
return 0
F( 1 )
F( 0 )
F( 3 )
F( 2 ) +
return
Fig Set of recursive calls to method Fibonacci (abbreviated as F).

54. 6.16 Recursion vs. Iteration
Uses repetition structures
while, do/while, for, foreach
Continues until counter fails repetition case
Recursion
Uses selection structures
if, if/else, switch
Repetition through method calls
Continues until a base case is reached
Creates a duplicate of the variables
Can consume memory and processor speed

55. Methods with the same name
6.17 Method Overloading
Methods with the same name
Can have the same name but need different arguments
Variables passed must be different
Either in type received or order sent
Usually perform the same task
On different data types

56. Two versions of the square method are called
1 // Fig. 6.18: MethodOverload.cs
2 // Using overloaded methods. 3
4 using System;
5 using System.Drawing;
6 using System.Collections;
7 using System.ComponentModel;
8 using System.Windows.Forms;
9 using System.Data; 10
11 public class MethodOverload : System.Windows.Forms.Form
12 {
private System.ComponentModel.Container components = null; 14
private System.Windows.Forms.Label outputLabel; 16
public MethodOverload() {
InitializeComponent(); 20
// call both versions of Square
outputLabel.Text =
"The square of integer 7 is " + Square( 7 ) +
"\nThe square of double 7.5 is " + Square ( 7.5 ); } 26
// Visual Studio .NET-generated code 28
MethodOverload.cs
Two versions of the square method are called

57. MethodOverload.cs Program Output
// first version, takes one integer
public int Square ( int x ) {
return x * x; } 34
// second version, takes one double
public double Square ( double y ) {
return y * y; } 40
[STAThread]
static void Main() {
Application.Run( new MethodOverload() ); } 46
47 } // end of class MethodOverload
One method takes an int as parameters
MethodOverload.cs Program Output
The other version of the method uses a double instead of an integer

58. MethodOverload2.cs Program Output
1 // Fig. 6.19: MethodOverload2.cs
2 // Overloaded methods with identical signatures and
3 // different return types. 4
5 using System; 6
7 class MethodOverload2
8 {
public int Square( double x ) {
return x * x; } 13
// second Square method takes same number,
// order and type of arguments, error
public double Square( double y ) {
return y * y; } 20
// main entry point for application
static void Main() {
int squareValue = 2;
Square( squareValue ); } 27
28 } // end of class MethodOverload2
MethodOverload2.cs Program Output
This method returns an integer
This method returns a double number
Since the compiler cannot tell which method to use based on passed values an error is generated