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### 06 procedures

1. 1. Chapter 6 - Procedures Outline 6.1 Introduction 6.2   Modules, Classes and Procedures 6.3   Sub Procedures 6.4   Function Procedures 6.5   Methods 6.6   Argument Promotion 6.7   Option Strict and Data Type Conversions 6.8   Value Types and Reference Types 6.9   Passing Arguments: Pass-by-Value vs. Pass-by-Reference 6.10   Duration of Identifiers 6.11   Scope Rules 6.12   Random-Number Generation 6.13   Example: Game of Chance 6.14   Recursion 6.15   Example Using Recursion: The Fibonacci Series 6.16   Recursion vs. Iteration
3. 3. 6.1 Introduction <ul><li>Divide and Conquer </li></ul><ul><ul><li>The best way to develop and maintain a large program is to construct it from small, manageable pieces. </li></ul></ul>
4. 4. 6.2 Modules, Classes and Procedures <ul><li>Framework Class Library </li></ul><ul><ul><li>Provides a rich collection of “prepackaged” classes and methods for performing many operations </li></ul></ul><ul><ul><ul><li>Mathematical calculations </li></ul></ul></ul><ul><ul><ul><li>String manipulations </li></ul></ul></ul><ul><ul><ul><li>Character manipulations </li></ul></ul></ul><ul><ul><ul><li>Input/output operations </li></ul></ul></ul><ul><ul><ul><li>Error checking </li></ul></ul></ul>
5. 5. 6.2 Modules, Classes and Procedures <ul><li>Programmer-defined procedures </li></ul><ul><ul><li>FCL cannot provide every conceivable feature that a programmer could want </li></ul></ul><ul><ul><li>Three types of procedures </li></ul></ul><ul><ul><ul><li>Sub procedures </li></ul></ul></ul><ul><ul><ul><li>Function procedures </li></ul></ul></ul><ul><ul><ul><li>Event procedures </li></ul></ul></ul><ul><ul><li>A procedure is invoked by a procedure call </li></ul></ul>
6. 6. 6.2 Modules, Classes and Procedures Fig. 6.1 Hierarchical boss procedure/worker procedure relationship. Boss Worker1 Worker2 Worker3 Worker4 Worker5
7. 7. 6.2 Modules, Classes and Procedures <ul><li>Division of code into procedures </li></ul><ul><ul><li>Several motivations to divide code into procedures </li></ul></ul><ul><ul><ul><li>Divide-and-conquer approach makes program development more manageable </li></ul></ul></ul><ul><ul><ul><li>Software reusability </li></ul></ul></ul><ul><ul><ul><li>Avoids the repetition of code in a program </li></ul></ul></ul>
8. 8. 6.2 Modules, Classes and Procedures <ul><li>Earlier programs had only one procedure that called FCL methods </li></ul><ul><li>Next program contains two customized procedures </li></ul>
9. 9. Payment.vb Program Output 1 ' Fig. 6.2: Payment.vb 2 ' Sub procedure that prints payment information. 3 4 Module modPayment 5 6 Sub Main() 7 8 ' call Sub procedure PrintPay 4 times 9 PrintPay( 40 , 10.5 ) 10 PrintPay( 38 , 21.75 ) 11 PrintPay( 20 , 13 ) 12 PrintPay( 50 , 14 ) 13 14 Console.ReadLine() ' prevent window from closing 15 End Sub ' Main 16 17 ' print amount of money earned in command window 18 Sub PrintPay( ByVal hours As Double , ByVal wage As Decimal ) 19 20 ' pay = hours * wage 21 Console.WriteLine( &quot;The payment is {0:C}&quot; , hours * wage) 22 End Sub ' PrintPay 23 24 End Module ' modPayment The payment is \$420.00 The payment is \$826.50 The payment is \$260.00 The payment is \$700.00 PrintPay executes when it is invoked by Main PrintPay receives the values of each argument and stores them in the parameters variables hours and wage Notice that PrintPay appears within modPayment . All procedures must be defined inside a module or a class
10. 10. 6.3 Sub Procedures <ul><li>Format of a procedure definition </li></ul><ul><ul><li>Sub procedure-name(parameter-list) </li></ul></ul><ul><ul><li>declarations and statements </li></ul></ul><ul><ul><li>End Sub </li></ul></ul><ul><li>Procedure header </li></ul><ul><ul><li>The first line is known as the procedure header </li></ul></ul><ul><li>Procedure-name </li></ul><ul><ul><li>Directly follows the Sub keyword </li></ul></ul><ul><ul><li>Can be any valid identifier </li></ul></ul><ul><ul><li>It is used to call this Sub procedure within the program </li></ul></ul><ul><li>Procedure body </li></ul><ul><ul><li>The declarations and statements in the procedure definition form the procedure body </li></ul></ul>
11. 11. 6.4 Function Procedures <ul><li>Similar to Sub procedures </li></ul><ul><li>One important difference </li></ul><ul><ul><li>Function procedures return a value to the caller </li></ul></ul>
12. 12. SquareInteger.vb 1 ' Fig. 6.3: SquareInteger.vb 2 ' Function procedure to square a number. 3 4 Module modSquareInteger 5 6 Sub Main() 7 Dim i As Integer ' counter 8 9 Console.WriteLine( &quot;Number&quot; & vbTab & &quot;Square&quot; & vbCrLf ) 10 11 ' square numbers from 1 to 10 12 For i = 1 To 10 13 Console.WriteLine(i & vbTab & Square(i)) 14 Next 15 16 End Sub ' Main 17 18 ' Function Square is executed 19 ' only when the function is explicitly called. 20 Function Square( ByVal y As Integer ) As Integer 21 Return y ^ 2 22 End Function ' Square 23 24 End Module ' modSquareInteger The For structure displays the results of squaring the Integer s from 1-10 Square is invoked with the expression Square(i) The Return statement terminates execution of the procedure and returns the result of y ^ 2
13. 13. SquareInteger.vb Program Output Number Square   1 1 2 4 3 9 4 16 5 25 6 36 7 49 8 64 9 81 10 100
14. 14. 6.4 Function Procedures <ul><li>Format of a Function procedure definition </li></ul><ul><ul><li>Function procedure-name(parameter-list) As return-type </li></ul></ul><ul><ul><li>declarations and statements </li></ul></ul><ul><ul><li>End Function </li></ul></ul><ul><li>Return-type </li></ul><ul><ul><li>Indicates the data type of the result returned from the Function to its caller </li></ul></ul><ul><li>Return expression </li></ul><ul><ul><li>Can occur anywhere in a Function </li></ul></ul><ul><ul><li>It returns exactly one value </li></ul></ul><ul><ul><li>Control returns immediately to the point at which that procedure was invoked </li></ul></ul>
15. 15. 6.5 Methods <ul><li>Definition of method </li></ul><ul><ul><li>A method is any procedure that is contained within a class </li></ul></ul><ul><ul><ul><li>FCL methods </li></ul></ul></ul><ul><ul><ul><li>Custom methods in programmer-defined classes </li></ul></ul></ul>
16. 16. Maximum.vb 1 ' Fig. 6.4: Maximum.vb 2 ' Program finds the maximum of three numbers input. 3 4 Public Class FrmMaximum 5 Inherits System.Windows.Forms.Form 6 7 ' prompts for three inputs 8 Friend WithEvents lblOne As System.Windows.Forms.Label 9 Friend WithEvents lblTwo As System.Windows.Forms.Label 10 Friend WithEvents lblThree As System.Windows.Forms.Label 11 12 ' displays result 13 Friend WithEvents lblMaximum As System.Windows.Forms.Label 14 15 ' read three numbers 16 Friend WithEvents txtFirst As System.Windows.Forms.TextBox 17 Friend WithEvents txtSecond As System.Windows.Forms.TextBox 18 Friend WithEvents txtThird As System.Windows.Forms.TextBox 19 20 ' reads inputs and calculate results 21 Friend WithEvents cmdMaximum As System.Windows.Forms.Button 22 23 ' Visual Studio .NET generated code 24 25 ' obtain values in each text box, call procedure Maximum 26 Private Sub cmdMaximum_Click( ByVal sender As System.Object, _ 27 ByVal e As System.EventArgs) Handles cmdMaximum.Click 28 These are declarations of all the controls used in the GUI. Create these components visually, using the Toolbox Remember that all forms inherit from class System.Windows.Forms.Form Event handler cmdMaximum_Click Handles the event in which Button cmdMaximum is clicked
17. 17. Maximum.vb Program Output 29 Dim value1, value2, value3 As Double 30 31 value1 = txtFirst.Text 32 value2 = txtSecond.Text 33 value3 = txtThird.Text 34 35 lblMaximum.Text = Maximum(value1, value2, value3) 36 End Sub ' cmdMaximum_Click 37 38 ' find maximum of three parameter values 39 Function Maximum( ByVal valueOne As Double , _ 40 ByVal valueTwo As Double , ByVal valueThree As Double ) 41 42 Return Math.Max(Math.Max(valueOne, valueTwo), valueThree) 43 End Function ' Maximum 44 45 End Class ' FrmMaximum The values in the three TextBox es are retrieved using the Text property Call to methods defined in the class that contains the method call need only specify the method name Call to methods that are defined in a class in the FCL must include the class name and the dot ( . ) operator
18. 18. 6.5 Methods Fig. 6.5 Parameter Info feature of the Visual Studio .NET IDE. Parameter Info window
19. 19. 6.5 Methods Fig. 6.6 IntelliSense feature of the Visual Studio .NET IDE.
20. 20. 6.5 Methods Fig. 6.7 Math class methods.
21. 21. 6.5 Methods Fig. 6.7 Math class methods.
22. 22. 6.6 Argument Promotion <ul><li>Coercion of arguments </li></ul><ul><ul><li>The forcing of arguments to be appropriate data type so that they can be passed to a procedure </li></ul></ul><ul><li>Widening conversion </li></ul><ul><ul><li>Occurs when a type is converted to another type without losing data </li></ul></ul><ul><li>Narrowing conversion </li></ul><ul><ul><li>Occurs when there is potential for data loss during the conversion </li></ul></ul>
23. 23. 6.6 Argument Promotion Fig. 6.8 Widening conversions.
24. 24. 6.7 Option Strict and Data-Type Conversions <ul><li>Option Explicit </li></ul><ul><ul><li>Set to On by default </li></ul></ul><ul><ul><li>Forces the programmer to declare explicitly all variables before they are used </li></ul></ul><ul><li>Option strict </li></ul><ul><ul><li>Set to Off by default </li></ul></ul><ul><ul><li>When set to On, it forces the programmer to perform an explicit conversion for all narrowing conversions </li></ul></ul><ul><li>Class Convert </li></ul><ul><ul><li>The methods in class Convert change data types explicitly </li></ul></ul>
25. 25. 6.7 Option Strict and Data-Type Conversions Fig. 6.9 Property Pages dialog with Option Strict set to On.
26. 26. 6.8 Value Types and Reference Types <ul><li>Variable of a value type </li></ul><ul><ul><li>Contains the actual data </li></ul></ul><ul><ul><li>Used for a single piece of data </li></ul></ul><ul><ul><ul><li>Integer </li></ul></ul></ul><ul><ul><ul><li>Double </li></ul></ul></ul><ul><li>Variable of a reference type </li></ul><ul><ul><li>Contains a location in memory where </li></ul></ul><ul><ul><li>Known as objects </li></ul></ul><ul><li>Literals </li></ul><ul><ul><li>Values typed directly in program code </li></ul></ul><ul><ul><li>Corresponds to one of the primitive data types </li></ul></ul>
27. 27. 6.8 Value Types and Reference Types Fig. 6.10 Visual Basic primitive data types.
28. 28. 6.8 Value Types and Reference Types Fig. 6.11 Literals with type characters.
29. 29. 6.9 Passing Arguments: Pass-by-Value vs. Pass-by-Reference <ul><li>Pass-by-value </li></ul><ul><ul><li>The program makes a copy of the argument’s value and passes that copy to the called procedure </li></ul></ul><ul><li>Pass-by-reference </li></ul><ul><ul><li>The caller gives the called procedure the ability to access and modify the caller’s original data directly. </li></ul></ul>
30. 30. ByRefTest.vb 1 ' Fig. 6.12: ByRefTest.vb 2 ' Demonstrates passing by reference. 3 4 Module modByRefTest 5 6 ' squares three values ByVal and ByRef, displays results 7 Sub Main() 8 Dim number1 As Integer = 2 9 10 Console.WriteLine ( &quot;Passing a value-type argument by value:&quot; ) 11 Console.WriteLine( &quot;Before calling SquareByValue, &quot; & _ 12 &quot;number1 is {0}&quot; , number1) 13 SquareByValue(number1) ' passes number1 by value 14 Console.WriteLine( &quot;After returning from SquareByValue, &quot; & _ 15 &quot;number1 is {0}&quot; & vbCrLf , number1) 16 17 Dim number2 As Integer = 2 18 19 Console.WriteLine ( &quot;Passing a value-type argument&quot; & _ 20 &quot; by reference:&quot; ) 21 Console.WriteLine( &quot;Before calling SquareByReference, &quot; & _ 22 &quot;number2 is {0}&quot; , number2) 23 SquareByReference(number2) ' passes number2 by reference 24 Console.WriteLine( &quot;After returning from &quot; & _ 25 &quot;SquareByReference, number2 is {0}&quot; & vbCrLf , number2) 26 27 Dim number3 As Integer = 2 28 When number1 is passed, a copy of the value is passed to the procedure A reference to the value stored in number2 is being passed
31. 31. ByRefTest.vb 29 Console.WriteLine ( &quot;Passing a value-type argument &quot; & _ 30 &quot; by reference, but in parentheses:&quot; ) 31 Console.WriteLine( &quot;Before calling SquareByReference &quot; & _ 32 &quot;using parentheses, number3 is {0}&quot; , number3) 33 SquareByReference((number3)) ' passes number3 by value 34 Console.WriteLine( &quot;After returning from &quot; & _ 35 &quot;SquareByReference, number3 is {0}&quot; , number3) 36 37 End Sub ' Main 38 39 ' squares number by value (note ByVal keyword) 40 Sub SquareByValue( ByVal number As Integer ) 41 Console.WriteLine( &quot;After entering SquareByValue, &quot; & _ 42 &quot;number is {0}&quot; , number) 43 number *= number 44 Console.WriteLine( &quot;Before exiting SquareByValue, &quot; & _ 45 &quot;number is {0}&quot; , number) 46 End Sub ' SquareByValue 47 48 ' squares number by reference (note ByRef keyword) 49 Sub SquareByReference( ByRef number As Integer ) 50 Console.WriteLine( &quot;After entering SquareByReference&quot; & _ 51 &quot;, number is {0}&quot; , number) 52 number *= number 53 Console.WriteLine( &quot;Before exiting SquareByReference&quot; & _ 54 &quot;, number is {0}&quot; , number) 55 End Sub ' SquareByReference 56 57 End Module ' modByRefTest ByVal indicates that value-type arguments should be passed by value ByRef gives direct access to the value stored in the original variable Enclosing arguments in parenthesis forces pass-by-value
32. 32. Program Output Passing a value-type argument by value: Before calling SquareByValue, number1 is 2 After entering SquareByValue, number is 2 Before exiting SquareByValue, number is 4 After returning from SquareByValue, number1 is 2   Passing a value-type argument by reference: Before calling SquareByReference, number2 is 2 After entering SquareByReference, number is 2 Before exiting SquareByReference, number is 4 After returning from SquareByReference, number2 is 4   Passing a value-type argument by reference, but in parentheses: Before calling SquareByReference using parentheses, number3 is 2 After entering SquareByReference, number is 2 Before exiting SquareByReference, number is 4 After returning from SquareByReference, number3 is 2
33. 33. 6.10 Duration of Identifiers <ul><li>Identifier’s duration </li></ul><ul><ul><li>Period during which the identifier exists in memory </li></ul></ul><ul><li>Identifier’s scope </li></ul><ul><ul><li>Portion of a program in which the variable’s identifier can be referenced </li></ul></ul><ul><li>Automatic duration </li></ul><ul><ul><li>Identifiers that represent local variables in a procedure have automatic duration </li></ul></ul><ul><li>Instance variable </li></ul><ul><ul><li>A variable declared in a class </li></ul></ul><ul><ul><li>They exist as long as their containing class is loaded in memory </li></ul></ul>
34. 34. 6.11 Scope Rules <ul><li>Possible scopes </li></ul><ul><ul><li>Class scope </li></ul></ul><ul><ul><ul><li>Begins at the class identifier after keyword Class and terminates at the End Class statement </li></ul></ul></ul><ul><ul><li>Module scope </li></ul></ul><ul><ul><ul><li>Variable declared in a module have module scope, which is similar to class scope </li></ul></ul></ul><ul><ul><li>Namespace scope </li></ul></ul><ul><ul><ul><li>Procedures defined in a module have namespace scope, which generally means that they may be accessed throughout a project </li></ul></ul></ul><ul><ul><li>Block scope </li></ul></ul><ul><ul><ul><li>Identifiers declared inside a block, such as the body of a procedure definition or the body of an If/Then selection structure, have block scope </li></ul></ul></ul>
35. 35. Scoping.vb 1 ' Fig. 6.13: Scoping.vb 2 ' Demonstrates scope rules and instance variables. 3 4 Public Class FrmScoping 5 Inherits System.Windows.Forms.Form 6 7 Friend WithEvents lblOutput As System.Windows.Forms.Label 8 9 ' Windows Form Designer generated code 10 11 ' instance variable can be used anywhere in class 12 Dim value As Integer = 1 13 14 ' demonstrates class scope and block scope 15 Private Sub FrmScoping_Load( ByVal sender As System.Object, _ 16 ByVal e As System.EventArgs) Handles MyBase .Load 17 18 ' variable local to FrmScoping_Load hides instance variable 19 Dim value As Integer = 5 20 21 lblOutput.Text = &quot;local variable value in&quot; & _ 22 &quot; FrmScoping_Load is &quot; & value 23 24 MethodA() ' MethodA has automatic local value 25 MethodB() ' MethodB uses instance variable value 26 MethodA() ' MethodA creates new automatic local value 27 MethodB() ' instance variable value retains its value 28 29 lblOutput.Text &= vbCrLf & vbCrLf & &quot;local variable &quot; & _ 30 &quot;value in CScoping_Load is &quot; & value 31 End Sub ' FrmScoping_Load 32 33 ' automatic local variable value hides instance variable 34 Sub MethodA() 35 Dim value As Integer = 25 ' initialized after each call This variable is hidden in any procedure that declares a variable named value Automatic variable value is destroyed when MethodA terminates None of the method calls modifies this variable – both methods refer to variables in other scopes
36. 36. Scoping.vb 36 37 lblOutput.Text &= vbCrLf & vbCrLf & &quot;local variable &quot; & _ 38 &quot;value in MethodA is &quot; & value & &quot; after entering MethodA&quot; 39 value += 1 40 lblOutput.Text &= vbCrLf & &quot;local variable &quot; & _ 41 &quot;value in MethodA is &quot; & value & &quot; before exiting MethodA&quot; 42 End Sub ' MethodA 43 44 ' uses instance variable value 45 Sub MethodB() 46 lblOutput.Text &= vbCrLf & vbCrLf & &quot;instance variable&quot; & _ 47 &quot; value is &quot; & value & &quot; after entering MethodB&quot; 48 value *= 10 49 lblOutput.Text &= vbCrLf & &quot;instance variable &quot; & _ 50 &quot;value is &quot; & value & &quot; before exiting MethodB&quot; 51 End Sub ' MethodB 52 53 End Class ' FrmScoping When MethodB procedure refers to variable value , the instance variable value (line 12) is used.
37. 37. 6.12 Random-Number Generation <ul><li>Random class </li></ul><ul><ul><li>Produces values at random </li></ul></ul><ul><ul><li>Keyword New creates an object of a specified type and returns the object’s location in memory </li></ul></ul><ul><ul><li>Next Method </li></ul></ul><ul><ul><ul><li>Generates a positive Integer value between zero and the constant Int32.MaxValue (2,147,483,647) </li></ul></ul></ul><ul><ul><ul><li>The current time of day becomes the seed value for the calculation </li></ul></ul></ul><ul><ul><ul><li>When a single argument is passed to Next , the values returned will be in the range from 0 to the value of that argument </li></ul></ul></ul><ul><ul><ul><ul><li>Scaling </li></ul></ul></ul></ul><ul><ul><ul><li>By passing two arguments, the programmer is allowed to specify the bottom range too </li></ul></ul></ul>
38. 38. RandomInteger.vb 1 ' Fig. 6.14: RandomInteger.vb 2 ' Generating random integers. 3 4 Imports System.Windows.Forms 5 6 Module modRandomInteger 7 8 Sub Main() 9 Dim randomObject As Random = New Random() 10 Dim randomNumber As Integer 11 Dim output As String = &quot;&quot; 12 Dim i As Integer 13 14 For i = 1 To 20 15 randomNumber = randomObject.Next( 1 , 7 ) 16 output &= randomNumber & &quot; &quot; 17 18 If i Mod 5 = 0 Then ' is i a multiple of 5? 19 output &= vbCrLf 20 End If 21 22 Next 23 24 MessageBox.Show(output, &quot;20 Random Numbers from 1 to 6&quot; , _ 25 MessageBoxButtons. OK , MessageBoxIcon. Information ) 26 End Sub ' Main 27 28 End Module ' modRandomInteger Note that we must use 7 as the second argument to produce integers in the range from 1-6 Go to the next line every time five numbers are generated
39. 39. RollDice.vb 1 ' Fig. 6.15: RollDice.vb 2 ' Rolling four dice. 3 4 Imports System.IO 5 6 Public Class FrmRollDice 7 Inherits System.Windows.Forms.Form 8 9 ' button for rolling dice 10 Friend WithEvents cmdRoll As System.Windows.Forms.Button 11 12 ' labels to display die images 13 Friend WithEvents lblDie1 As System.Windows.Forms.Label 14 Friend WithEvents lblDie2 As System.Windows.Forms.Label 15 Friend WithEvents lblDie3 As System.Windows.Forms.Label 16 Friend WithEvents lblDie4 As System.Windows.Forms.Label 17 18 ' Visual Studio .NET generated code 19 20 ' declare Random object reference 21 Dim randomNumber As Random = New Random() 22 23 ' display results of four rolls 24 Private Sub cmdRoll_Click( ByVal sender As System.Object, _ 25 ByVal e As System.EventArgs) Handles cmdRoll.Click 26 27 ' method randomly assigns a face to each die 28 DisplayDie(lblDie1) 29 DisplayDie(lblDie2) 30 DisplayDie(lblDie3) 31 DisplayDie(lblDie4) 32 End Sub ' cmdRoll_Click 33 Event-handling method cmdRoll_Click , executes whenever the user clicks cmdRoll RandomNumber is an instance variable of FrmRollDice . This allows the same Random object to be used each time DisplayDie executes
40. 40. RollDice.vb 34 ' get a random die image 35 Sub DisplayDie( ByVal dieLabel As Label) 36 37 ' generate random integer in range 1 to 6 38 Dim face As Integer = randomNumber.Next( 1 , 7 ) 39 40 ' load corresponding image 41 dieLabel.Image = Image.FromFile( _ 42 Directory.GetCurrentDirectory & &quot;Imagesdie&quot; & _ 43 face & &quot;.png&quot; ) 44 End Sub ' DisplayDie 45 46 End Class ' FrmRollDice Image property displays an image on the label Class Image is contained in the System.Drawing namespace, which is imported by default in all Windows Applications Method Directory.GetCurrentDirectory returns the location of the folder in which the current project is located, including bin
41. 41. RollTwelveDice.vb 1 ' Fig. 6.16: RollTwelveDice.vb 2 ' Rolling 12 dice with frequency chart. 3 4 Imports System.IO 5 6 Public Class FrmRollTwelveDice 7 Inherits System.Windows.Forms.Form 8 9 ' labels to display die images 10 Friend WithEvents lblDie1 As System.Windows.Forms.Label 11 Friend WithEvents lblDie2 As System.Windows.Forms.Label 12 Friend WithEvents lblDie3 As System.Windows.Forms.Label 13 Friend WithEvents lblDie4 As System.Windows.Forms.Label 14 Friend WithEvents lblDie5 As System.Windows.Forms.Label 15 Friend WithEvents lblDie6 As System.Windows.Forms.Label 16 Friend WithEvents lblDie7 As System.Windows.Forms.Label 17 Friend WithEvents lblDie8 As System.Windows.Forms.Label 18 Friend WithEvents lblDie9 As System.Windows.Forms.Label 19 Friend WithEvents lblDie10 As System.Windows.Forms.Label 20 Friend WithEvents lblDie11 As System.Windows.Forms.Label 21 Friend WithEvents lblDie12 As System.Windows.Forms.Label 22 23 ' displays roll frequencies 24 Friend WithEvents displayTextBox As _ 25 System.Windows.Forms.TextBox 26 27 ' Visual Studio .NET generated code 28 29 ' declarations 30 Dim randomObject As Random = New Random() 31 Dim ones, twos, threes, fours, fives, sixes As Integer 32 We declare counters for each of the possible rolls The TextBox is used to display the cumulative frequencies of each face
42. 42. RollTwelveDice.vb 35 Private Sub cmdRoll_Click _ 34 ( ByVal sender As System.Object, _ 35 ByVal e As System.EventArgs) Handles cmdRoll.Click 36 37 ' assign random faces to 12 dice using DisplayDie 38 DisplayDie(lblDie1) 39 DisplayDie(lblDie2) 40 DisplayDie(lblDie3) 41 DisplayDie(lblDie4) 42 DisplayDie(lblDie5) 43 DisplayDie(lblDie6) 44 DisplayDie(lblDie7) 45 DisplayDie(lblDie8) 46 DisplayDie(lblDie9) 47 DisplayDie(lblDie10) 48 DisplayDie(lblDie11) 49 DisplayDie(lblDie12) 50 51 Dim total As Integer = ones + twos + threes + fours + _ 52 fives + sixes 53 54 Dim output As String 55 56 ' display frequencies of faces 57 output = &quot;Face&quot; & vbTab & vbTab & _ 58 &quot;Frequency&quot; & vbTab & &quot;Percent&quot; 59 60 output &= vbCrLf & &quot;1&quot; & vbTab & vbTab & ones & _ 61 vbTab & vbTab & String .Format( &quot;{0:P}&quot; , ones / total) 62 63 output &= vbCrLf & &quot;2&quot; & vbTab & vbTab & twos & vbTab & _ 64 vbTab & String .Format( &quot;{0:P}&quot; , twos / total) 65 66 output &= vbCrLf & &quot;3&quot; & vbTab & vbTab & threes & vbTab & _ 67 vbTab & String .Format( &quot;{0:P}&quot; , threes / total) The “P” format code is used to display the frequency of each roll as percentages
43. 43. RollTwelveDice.vb 68 69 output &= vbCrLf & &quot;4&quot; & vbTab & vbTab & fours & vbTab & _ 70 vbTab & String .Format( &quot;{0:P}&quot; , fours / total) 71 72 output &= vbCrLf & &quot;5&quot; & vbTab & vbTab & fives & vbTab & _ 73 vbTab & String .Format( &quot;{0:P}&quot; , fives / total) 74 75 output &= vbCrLf & &quot;6&quot; & vbTab & vbTab & sixes & vbTab & _ 76 vbTab & String .Format( &quot;{0:P}&quot; , sixes / total) & vbCrLf 77 78 displayTextBox.Text = output 79 End Sub ' cmdRoll_Click 80 81 ' display a single die image 82 Sub DisplayDie( ByVal dieLabel As Label) 83 84 Dim face As Integer = randomObject.Next( 1 , 7 ) 85 86 dieLabel.Image = _ 87 Image.FromFile(Directory.GetCurrentDirectory & _ 88 &quot;Imagesdie&quot; & face & &quot;.png&quot; ) 89 90 ' maintain count of die faces 91 Select Case face 92 93 Case 1 94 ones += 1 95 96 Case 2 97 twos += 1 98 99 Case 3 100 threes += 1 101 Select Case is used to calculate the frequency
44. 44. RollTwelveDice.vb 102 Case 4 103 fours += 1 104 105 Case 5 106 fives += 1 107 108 Case 6 109 sixes += 1 110 111 End Select 112 113 End Sub ' DisplayDie 114 115 End Class ' FrmRollTwelveDice
45. 45. 6.13 Example: Game of Chance <ul><li>Craps </li></ul><ul><ul><li>The next application simulates one of the most popular games of chance </li></ul></ul><ul><ul><li>The player must roll two dice on the first and all subsequent rolls </li></ul></ul>
46. 46. CrapsGame.vb 1 ' Fig 6.17: CrapsGame.vb 2 ' Playing a craps game. 3 4 Imports System.IO 5 6 Public Class FrmCrapsGame 7 Inherits System.Windows.Forms.Form 8 9 Friend WithEvents cmdRoll As Button ' rolls dice 10 Friend WithEvents cmdPlay As Button ' starts new game 11 12 ' dice displayed after each roll 13 Friend WithEvents picDie1 As PictureBox 14 Friend WithEvents picDie2 As PictureBox 15 16 ' pointDiceGroup groups dice representing player's point 17 Friend WithEvents pointDiceGroup As GroupBox 18 Friend WithEvents picPointDie1 As PictureBox 19 Friend WithEvents picPointDie2 As PictureBox 20 21 Friend WithEvents lblStatus As Label 22 23 ' Visual Studio .NET generated code 24 25 ' die-roll constants 26 Enum DiceNames 27 SNAKE_EYES = 2 28 TREY = 3 29 CRAPS = 7 30 YO_LEVEN = 11 31 BOX_CARS = 12 32 End Enum 33 A GroupBox is a container used to group related components Enum erations are used to define groups of related constants
47. 47. CrapsGame.vb 34 ' file-name and directory constants 35 Const FILE_PREFIX As String = &quot;/images/die&quot; 36 Const FILE_SUFFIX As String = &quot;.png&quot; 37 38 Dim myPoint As Integer 39 Dim myDie1 As Integer 40 Dim myDie2 As Integer 41 Dim randomObject As Random = New Random() 42 43 ' begins new game and determines point 44 Private Sub cmdPlay_Click( ByVal sender As System.Object, _ 45 ByVal e As System.EventArgs) Handles cmdPlay.Click 46 47 ' initialize variables for new game 48 myPoint = 0 49 pointDiceGroup.Text = &quot;Point&quot; 50 lblStatus.Text = &quot;&quot; 51 52 ' remove point-die images 53 picPointDie1.Image = Nothing 54 picPointDie2.Image = Nothing 55 56 Dim sum As Integer = RollDice() 57 58 ' check die roll 59 Select Case sum 60 61 Case DiceNames. CRAPS , DiceNames. YO_LEVEN 62 63 ' disable roll button 64 cmdRoll.Enabled = False 65 lblStatus.Text = &quot;You Win!!!&quot; 66 Keyword Const creates a single constant identifier in which values cannot be modified after they are declared Keyword Nothing can be used with reference-type variables to specify that no object is associated with the variable Setting the Image property to Nothing causes the PictureBoxes to appear blank The Select structure analyzes the roll returned by RollDice to determine how play should continue
48. 48. CrapsGame.vb 67 Case DiceNames. SNAKE_EYES , _ 68 DiceNames. TREY , DiceNames. BOX_CARS 69 70 cmdRoll.Enabled = False 71 lblStatus.Text = &quot;Sorry. You Lose.&quot; 72 73 Case Else 74 myPoint = sum 75 pointDiceGroup.Text = &quot;Point is &quot; & sum 76 lblStatus.Text = &quot;Roll Again!&quot; 77 DisplayDie(picPointDie1, myDie1) 78 DisplayDie(picPointDie2, myDie2) 79 cmdPlay.Enabled = False 80 cmdRoll.Enabled = True 81 82 End Select 83 84 End Sub ' cmdPlay_Click 85 86 ' determines outcome of next roll 87 Private Sub cmdRoll_Click( ByVal sender As System.Object, _ 88 ByVal e As System.EventArgs) Handles cmdRoll.Click 89 90 Dim sum As Integer = RollDice() 91 92 ' check outcome of roll 93 If sum = myPoint Then 94 lblStatus.Text = &quot;You Win!!!&quot; 95 cmdRoll.Enabled = False 96 cmdPlay.Enabled = True 97 ElseIf sum = DiceNames. CRAPS Then 98 lblStatus.Text = &quot;Sorry. You Lose.&quot; 99 cmdRoll.Enabled = False 100 cmdPlay.Enabled = True 101 End If Disabling a Button causes no action to be performed when the Button is clicked
49. 49. CrapsGame.vb 102 103 End Sub ' cmdRoll_Click 104 105 ' display die image 106 Sub DisplayDie( ByVal picDie As PictureBox, _ 107 ByVal face As Integer ) 108 109 ' assign die image to picture box 110 picDie.Image = _ 111 Image.FromFile(Directory.GetCurrentDirectory & _ 112 FILE_PREFIX & face & FILE_SUFFIX ) 113 End Sub ' DisplayDie 114 115 ' generate random die rolls 116 Function RollDice() As Integer 117 Dim die1, die2 As Integer 118 119 ' determine random integer 120 die1 = randomObject.Next( 1 , 7 ) 121 die2 = randomObject.Next( 1 , 7 ) 122 123 ' display rolls 124 DisplayDie(picDie1, die1) 125 DisplayDie(picDie2, die2) 126 127 ' set values 128 myDie1 = die1 129 myDie2 = die2 130 131 Return die1 + die2 132 End Function ' RollDice 133 134 End Class ' FrmCrapsGame RollDice generates two random numbers and calls method DisplayDie , which loads an appropriate die image on the PictureBox passed to it.
50. 50. CrapsGame.vb GroupBox PictureBoxes (displaying images)
51. 51. 6.14 Recursion <ul><li>Recursive procedure </li></ul><ul><ul><li>It is a procedure that calls itself either directly or indirectly </li></ul></ul><ul><ul><li>It is called to solve a problem </li></ul></ul><ul><ul><li>The procedure knows how to solve only the simples case (base case) </li></ul></ul><ul><ul><li>For complex problems, the procedure divides the problem into a piece that it can perform and a piece that it does not know how to perform </li></ul></ul><ul><ul><li>Recursive call </li></ul></ul><ul><ul><ul><li>The procedure invokes a fresh copy of itself to work on the smaller problem </li></ul></ul></ul>
52. 52. 6.14 Recursion Fig. 6.18 Recursive evaluation of 5!. 5! 5 * 4! 4 * 3! 3 * 2! 2 * 1! 1 5! 5 * 4! 4 * 3! 3 * 2! 2 * 1! 1 Final value = 120 5! = 5 * 24 = 120 is returned 4! = 4 * 6 = 24 is returned 3! = 3 * 2 = 6 is returned 2! = 2 * 1 = 2 is returned 1 returned (a) Procession of recursive calls (b) Values returned from each recursive call
53. 53. Factorial.vb 1 ' Fig. 6.19: Factorial.vb 2 ' Calculating factorials using recursion. 3 4 Public Class FrmFactorial 5 Inherits System.Windows.Forms.Form 6 7 Friend WithEvents lblEnter As Label ' prompts for Integer 8 Friend WithEvents lblFactorial As Label ' indicates output 9 10 Friend WithEvents txtInput As TextBox ' reads an Integer 11 Friend WithEvents txtDisplay As TextBox ' displays output 12 13 Friend WithEvents cmdCalculate As Button ' generates output 14 15 ' Visual Studio .NET generated code 16 17 Private Sub cmdCalculate_Click( ByVal sender As System.Object, _ 18 ByVal e As System.EventArgs) Handles cmdCalculate.Click 19 20 Dim value As Integer = Convert.ToInt32(txtInput.Text) 21 Dim i As Integer 22 Dim output As String 23 24 txtDisplay.Text = &quot;&quot; 25 26 For i = 0 To value 27 txtDisplay.Text &= i & &quot;! = &quot; & Factorial(i) & vbCrLf 28 Next 29 30 End Sub ' cmdCalculate_Click Conversion from String to Integer
54. 54. Factorial.vb 31 32 ' recursively generates factorial of number 33 Function Factorial( ByVal number As Long ) As Long 34 35 If number <= 1 Then ' base case 36 Return 1 37 Else 38 Return number * Factorial(number - 1 ) 39 End If 40 41 End Function ' Factorial 42 43 End Class ' FrmFactorial If number is greater than 1 , a recursive call to Factorial is made with a slightly simpler problem Forgetting to return a value from a recursive procedure can result in logic errors
55. 55. 6.15 Example Using Recursion: Fibonacci Series <ul><li>The Fibonacci series </li></ul><ul><ul><li>It begins with 0 and 1 and defines each subsequent Fibonacci number as the sum of the previous two Fibonacci numbers </li></ul></ul><ul><li>Golden ratio </li></ul><ul><ul><li>The ratio of successive fibonacci numbers converges on a constant value near 1.618 </li></ul></ul><ul><li>Fibonacci method </li></ul><ul><ul><li>Each invocation of the method that does not match one of the base cases results in two additional recursive calls to the method </li></ul></ul><ul><ul><li>Fibonacci value of 30 requires 2,692,537 </li></ul></ul>
56. 56. Fibonacci.vb 1 ' Fig. 6.20: Fibonacci.vb 2 ' Demonstrating Fibonacci sequence recursively. 3 4 Public Class FrmFibonacci 5 Inherits System.Windows.Forms.Form 6 7 Friend WithEvents lblPrompt As Label ' prompts for input 8 Friend WithEvents lblResult As Label ' displays result 9 10 Friend WithEvents cmdCalculate As Button ' calculates result 11 12 Friend WithEvents txtInputBox As TextBox ' reads an Integer 13 14 ' Visual Studio .NET generated code 15 16 ' displays Fibonacci number in txtInputBox 17 Private Sub cmdCalculate_Click( ByVal sender As System.Object, _ 18 ByVal e As System.EventArgs) Handles cmdCalculate.Click 19 20 ' read input 21 Dim number As Integer = Convert.ToInt32(txtInputBox.Text) 22 23 lblResult.Text = &quot;Fibonacci Value is &quot; & Fibonacci(number) 24 End Sub ' cmdCalculate_Click 25 26 ' calculate Fibonacci value recusively 27 Function Fibonacci( ByVal number As Integer ) As Long 28 29 ' check for base cases 30 If number = 1 OrElse number = 0 Then 31 Return number 32 Else 33 Return Fibonacci(number - 1 ) + Fibonacci(number - 2 ) 34 End If 35 This call to Fibonacci is not a recursive call If number is greater than 1 , the recursion step generates two recursive calls
57. 57. Fibonacci.vb 36 End Function ' Fibonacci 37 38 End Class ' FrmFibonacci
58. 58. 6.15 Example Using Recursion: Fibonacci Series Fig. 6.21 Recursive calls to method Fibonacci (abbreviated as F). Fibonacci( 3 ) Fibonacci( 2 ) Fibonacci( 1 ) Fibonacci( 0 ) Fibonacci( 1 ) return 1 return return 1 return 0 return
59. 59. 6.16 Recursion vs. Iteration <ul><li>Iteration </li></ul><ul><ul><li>Involves an explicit repetition structure </li></ul></ul><ul><ul><li>Uses a repetition structure </li></ul></ul><ul><ul><ul><li>For , While or Do / Loop Until </li></ul></ul></ul><ul><li>Recursion </li></ul><ul><ul><li>Achieves repetition through repeated procedure calls </li></ul></ul><ul><ul><li>Uses a selection structure </li></ul></ul><ul><ul><ul><li>If / Then , If / Then / Else or Select </li></ul></ul></ul><ul><ul><li>Recursive calls take time and consume additional memory </li></ul></ul>
60. 60. 6.17 Procedure Overloading and Optional Arguments <ul><li>Overloading </li></ul><ul><ul><li>Allows multiple procedures with the same name, but differing numbers and types of arguments </li></ul></ul><ul><ul><li>The overloading of procedures that perform closely related tasks can make programs more readable and understandable </li></ul></ul><ul><li>Optional arguments </li></ul><ul><ul><li>Defining an argument as optional allows the calling procedure to decide what arguments to pass </li></ul></ul>
61. 61. Overload.vb 1 ' Fig. 6.22: Overload.vb 2 ' Using overloaded methods. 3 4 Public Class FrmOverload 5 Inherits System.Windows.Forms.Form 6 7 Friend WithEvents outputLabel As Label 8 9 ' Visual Studio .NET generated code 10 11 Private Sub FrmOverload_Load( ByVal sender As System.Object, _ 12 ByVal e As System.EventArgs) Handles MyBase .Load 13 14 outputLabel.Text = &quot;The square of Integer 7 is &quot; & _ 15 square( 7 ) & vbCrLf & &quot;The square of Double &quot; & _ 16 &quot;7.5 is &quot; & square( 7 . 5 ) 17 End Sub ' FrmOverload_Load 18 19 Function Square( ByVal value As Integer ) As Integer 20 Return Convert.ToInt32(value ^ 2 ) 21 End Function ' Square 22 23 Function Square( ByVal value As Double ) As Double 24 Return value ^ 2 25 End Function ' Square 26 27 End Class ' FrmOverload The compiler uses a logical name to differ between the two Square methods The compiler might use the logical name “ Square of Integer ” “ Square of Double ” for the Square method that specifies a Double parameter
62. 62. Overload2.vb 1 ' Fig. 6.23: Overload2.vb 2 ' Using overloaded procedures with identical signatures and 3 ' different return types. 4 5 Public Class FrmOverload2 6 Inherits System.Windows.Forms.Form 7 8 Friend WithEvents outputLabel As Label 9 10 ' Visual Studio .NET generated code 11 12 Private Sub FrmOverload2_Load( ByVal sender As System.Object, _ 13 ByVal e As System.EventArgs) Handles MyBase .Load 14 15 outputLabel.Text = &quot;The square of Integer 7 is &quot; & _ 16 square( 7 ) & vbCrLf & &quot;The square of Double &quot; & _ 17 &quot;7.5 is &quot; & square( 7 . 5 ) 18 End Sub ' FrmOverload2_Load 19 20 Function Square( ByVal value As Double ) As Integer 21 Return Convert.ToInt32(value ^ 2 ) 22 End Function ' Square 23 24 Function Square( ByVal value As Double ) As Double 25 Return value ^ 2 26 End Function ' Square 27 28 End Class ' FrmOverload2 Procedure calls cannot be distinguished by return type
63. 63. Overload2.vb Program Output The creating of overloaded procedures with identical parameter lists and different return types produces a syntax error
64. 64. 6.17.2 Optional Arguments <ul><li>Optional </li></ul><ul><ul><li>Optional arguments are specified in the procedure header with keyword Optional </li></ul></ul><ul><li>Syntax errors </li></ul><ul><ul><li>Not specifying a default value for an Optional parameter is a syntax error </li></ul></ul><ul><ul><li>Declaring a non- Optional parameter to the right of an Optional parameter is a syntax error </li></ul></ul>
65. 65. Power.vb 1 ' Fig 6.24 Power.vb 2 ' Calculates the power of a value, defaults to square. 3 4 Public Class FrmPower 5 Inherits System.Windows.Forms.Form 6 7 Friend WithEvents txtBase As TextBox ' reads base 8 Friend WithEvents txtPower As TextBox ' reads power 9 10 Friend WithEvents inputGroup As GroupBox 11 12 Friend WithEvents lblBase As Label ' prompts for base 13 Friend WithEvents lblPower As Label ' prompts for power 14 Friend WithEvents lblOutput As Label ' displays output 15 16 Friend WithEvents cmdCalculate As Button ' generates output 17 18 ' Visual Studio .NET generated code 19 20 ' reads input and displays result 21 Private Sub cmdCalculate_Click( ByVal sender As System.Object, _ 22 ByVal e As System.EventArgs) Handles cmdCalculate.Click 23 24 Dim value As Integer 25 26 ' call version of Power depending on power input 27 If Not txtPower.Text = &quot;&quot; Then 28 value = Power(Convert.ToInt32(txtBase.Text), _ 29 Convert.ToInt32(txtPower.Text)) 30 Else 31 value = Power(Convert.ToInt32(txtBase.Text)) 32 End If 33 34 lblOutput.Text = Convert.ToString(value) 35 End Sub ' cmdCalculate_Click Determines whether txtPower contains a value
66. 66. Power.vb 36 37 ' use iteration to calculate power 38 Function Power( ByVal base As Integer , _ 39 Optional ByVal exponent As Integer = 2 ) As Integer 40 41 Dim total As Integer = 1 42 Dim i As Integer 43 44 For i = 1 To exponent 45 total *= base 46 Next 47 48 Return total 49 End Function ' Power 50 51 End Class ' FrmPower When omitted, the Optional argument defaults to the value 2
67. 67. 6.18 Modules <ul><li>Modules </li></ul><ul><ul><li>Used to group related procedures so that they can be reused in other projects </li></ul></ul><ul><ul><li>Similar in many ways to classes </li></ul></ul><ul><ul><li>Should be self-contained </li></ul></ul>
68. 68. DiceModule.vb 1 ' Fig. 6.25: DiceModule.vb 2 ' A collection of common dice procedures. 3 4 Imports System.IO 5 6 Module modDice 7 8 Dim randomObject As Random = New Random() 9 10 ' rolls single die 11 Function RollDie() As Integer 12 Return randomObject.Next( 1 , 7 ) 13 End Function ' RollDie 14 15 ' die summation procedure 16 Function RollAndSum( ByVal diceNumber As Integer ) _ 17 As Integer 18 19 Dim i As Integer 20 Dim sum As Integer = 0 21 22 For i = 1 To diceNumber 23 sum += RollDie() 24 Next 25 26 Return sum 27 End Function ' RollAndSum modDice groups several dice-related procedures into a module for reuse in other programs that use dice
69. 69. DiceModule.vb 28 29 ' returns die image 30 Function GetDieImage( ByVal dieValue As Integer , _ 31 Optional ByVal baseImageName As String = &quot;die&quot; ) _ 32 As System.Drawing.Image 33 34 Return Image.FromFile( _ 35 Directory.GetCurrentDirectory & _ 36 &quot;Images&quot; & baseImageName & dieValue & &quot;.png&quot; ) 37 End Function ' GetDieImage 38 39 End Module ' modDice Optional parameter baseImageName represents the prefix of the image name to be used
70. 70. DiceModuleTest.vb 1 ' Fig. 6.26: DiceModuleTest.vb 2 ' Demonstrates modDiceModule procedures 3 4 Imports System.Drawing 5 6 Public Class FrmDiceModuleTest 7 Inherits System.Windows.Forms.Form 8 9 Friend WithEvents lblSum As Label ' displays 10-roll sum 10 11 Friend WithEvents diceGroup As GroupBox 12 13 ' dice images 14 Friend WithEvents picDie1 As PictureBox 15 Friend WithEvents picDie2 As PictureBox 16 17 Friend WithEvents cmdRollDie1 As Button ' rolls blue die 18 Friend WithEvents cmdRollTen As Button ' simulates 10 rolls 19 Friend WithEvents cmdRollDie2 As Button ' rolls red die 20 21 ' Visual Studio .NET generated code 22 23 Private Sub cmdRollDie1_Click( ByVal sender As System.Object, _ 24 ByVal e As System.EventArgs) Handles cmdRollDie1.Click 25 26 picDie1.Image = modDice.GetDieImage(modDice.RollDie()) 27 End Sub ' cmdRollDie1_Click 28 29 Private Sub cmdRollDie2_Click( ByVal sender As System.Object, _ 30 ByVal e As System.EventArgs) Handles cmdRollDie2.Click 31 32 picDie2.Image = modDice.GetDieImage(modDice.RollDie(), _ 33 &quot;redDie&quot; ) 34 End Sub ' cmdRollDie2_Click 35 cmdRollDie2_Click uses the Optional argument to prefix the image name and select a different image We call procedures contained in modDice by following the module name with the dot ( . ) operator and the procedure name
71. 71. DiceModuleTest.vb 36 Private Sub cmdRollTen_Click( ByVal sender As System.Object, _ 37 ByVal e As System.EventArgs) Handles cmdRollTen.Click 38 39 lblSum.Text = Convert.ToString(modDice.RollAndSum( 10 )) 40 End Sub ' cmdRollTen_Click 41 42 End Class ' FrmDiceModuleTest This procedure sets the Text property of lblSum to the result of 10 rolls