1. Program Modules in C# Modules The .NET Framework Class Library (FCL)
Method
The .NET Framework Class Library (FCL)
Helps to increase reusability
Console
MessageBox
Math calculations, character and string manipulations, I/O operations, error checking

2. Math Class Methods
Class Math is located in namespace System (not necessary to add an assembly reference)
Using methods
ClassName.MethodName( argument1, arument2, … )
Example: Math.Sqrt (900.0)
List of methods are in text
Abs, Ceiling, Cos, Exp, Floor, Log, Max, Min, Pow, Sin, Sqrt, Tan
Constants
Math.PI = …
Math.E = …

3. Methods Variables Reasons for using Methods
Declared in a method = local variables
Declared outside a method = global variables
Reasons for using Methods
“Divide and conquer”  Decomposition
Cut down on repetition
Reusability

4. Method Definitions Writing a custom method
Header and Body same as in C++
All methods must be defined inside of a class
Methods can return at most one value!!!

5. More I/O Until now Next Input from Console
Output to Console or MessageBox
These can only handle one input or output value at a time
Next
Attaching multiple GUI components to an application and event handling
Button GUI component
Requires an event handler

6. Instantiation of SquareIntForm

7. Destructor
InitializeComponent method in this generated code – defines non-default properties for components on form

8. Constructor Start of class SquareInt. It implements a Form {
// SquareIntForm.cs // A programmer-defined Square method using System; // includes basic data types using System.Drawing; // for graphics capabilities using System.Collections; // for complex data structures using System.ComponentModel; // controls component behavior using System.Windows.Forms; // for GUI development using System.Data; // for reading outside data namespace SquareInt {
// form used to display results of squaring 10 numbers
public partial class SquareIntForm : Form
public SquareIntForm()
InitializeComponent(); }
Start of class SquareInt. It implements a Form
Constructor

9. The Square method. Receives one integer and returns an integer
// Square method definition
int Square( int y ) {
return y * y; // return square of y
} // end method Square
private void calculateButton_Click (object sender,
System.EventArgs e)
outputLabel.Text = "";
// loop 10 times
for ( int counter = 1; counter <= 10; counter++ )
// calculate square of counter and store in result
result = Square( counter );
// append result to output string
outputLabel.Text += "The square of " + counter +
" is " + result + "\n"; }
} // end calculateButton_Click
} // end of class SquareInt
} // end namespace
Double-click on button to generate this event handler. Code it.
ReInit for each button click!

10. // MaximumValue.Designer.cs
+ Windows Form Designer generated code
private System.Windows.Forms.Label firstNumberLabel;
private System.Windows.Forms.Label secondNumberLabel;
private System.Windows.Forms.Label thirdNumberLabel;
private System.Windows.Forms.Label maximumLabel;
private System.Windows.Forms.TextBox firstNumberTextBox;
private System.Windows.Forms.TextBox secondNumberTextBox;
private System.Windows.Forms.TextBox thirdNumberTextBox;
private System.Windows.Forms.Button calculateButton;
Prompts for Text Boxes
Input values in Text Boxes

11. double Maximum( double x, double y, double z ) {
// MaximumValueForm.cs
// Finding the maximum of three double values.
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
// Method Maximum uses method Math.Max to determine the
// maximum value among the three double arguments
double Maximum( double x, double y, double z ) {
return Math.Max( x, Math.Max( y, z ) ); }
The use of Math.Max uses the Max method in class Math. The dot operator is used to call it.

12. Double.Parse( firstNumberTextBox.Text );
// get the floating-point values that the user entered and
// invoke method Maximum to determine the maximum value
private void calculateButton_Click (object sender,
System.EventArgs e) {
// get inputted values and convert strings to doubles
double number1 =
Double.Parse( firstNumberTextBox.Text );
double number2 =
Double.Parse( secondNumberTextBox.Text );
double number3 =
Double.Parse( thirdNumberTextBox.Text );
// invoke method Maximum to determine the largest value
double maximum = Maximum( number1, number2, number3 );
// display maximum value
maximumLabel.Text = "maximum is: " + maximum;
} // end method calculateButton_Click
} // end class MaximumValue
} // end namespace MaximumValue
Gets input from Text Boxes when button clicked
Displays output in Label

13. Calling Methods Three ways to call methods Method name itself
Square (x)
Maximum (num1, num2, num3)
Reference to an object following by the dot operator and the method name
string1.CompareTo (string2)
Class name followed by dot and method name (static method)
Math.Max( y, z )

14. Argument Promotion Implicit Conversion Explicit Conversion
Only done if no data will be lost
Coercion of arguments to methods and in mixed-type expressions to a higher type
Explicit Conversion
Done with cast or class Convert in namespace System
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
Cast Example: int result = Square ( (int ) y );

15. C# Namespaces FCL is composed of namespaces
A namespace is a group of classes and their methods
Namespaces are stored in .dll files called assemblies
Included in a program with the using keyword
System.Console.WriteLine  Console.WriteLine
Must add a reference to appropriate assembly (except for namespace System)
FCL includes many names (look up “.NET Framework, class library” in the help doc)

16. C# Namespaces in FCL

17. Value Types and Reference Types Types (C# Reference) in MSDN Library
Contains data of the specified type
Built in
Programmer created - structs and enumerations
Reference types
Contain an address
Built-in (string and object)
Programmer created - Classes and Interfaces and Delegates
All values are 32bit allowing cross-platform use

18. Passing Arguments: Call-By-Value vs. Call-By-Reference
Value types are passed by value and reference types are passed by reference
To pass a value type by reference?
The ref keyword specifies by-reference
can modify original variable
used with variables already initialized
The out keyword means a called method will initialize it

19. 9 // 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; }
When passing a value by reference the value will be altered in the rest of the program as well
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. Random Number Generation
Class Random within namespace System
Numbers are generated using an equation with a seed - 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 value between x and up to but not including y

21. 16 Random randomInteger = new Random();
1 // Different RandomIntForm.cs
2 // Random integers.
4 using System;
5 using System.Windows.Forms; 6
7 // calculates and displays 20 random integers
8 public partial class RandomIntForm : Form
9 {
// main entry point for application
public RandomIntForm ()
{ InitializeComponent ();
int value;
string output = ""; 15
16 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";
} // end for structure
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

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

23. RollDie.cs - Rolling 4 dice.

24. 20 private System.Windows.Forms.Label dieLabel1;
// THE AUTO GENERATED CODE for the application RollDie
private System.ComponentModel.Container components = null;
private System.Windows.Forms.Button rollButton;
20 private System.Windows.Forms.Label dieLabel1;
21 private System.Windows.Forms.Label dieLabel2;
22 private System.Windows.Forms.Label dieLabel3;
23 private System.Windows.Forms.Label dieLabel4;
1 // RollDie.cs: Rolling 4 dice.
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 24
26 // form simulates the rolling of 4 dice, and displays them
14 public partial class RollDieForm : Form
15 {
private Random randomNumber = new Random();
public RollDieForm() {
InitializeComponent(); } 32

25. 41 DisplayDie( dieLabel1 );
// 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 );
} // end rollButton_Click 47
// determines image to be displayed by current die
49 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" ); }
Pass the labels to be assigned data
Will return a random integer from 0 up to 6

27. 17 private System.Windows.Forms.Button rollButton;
private System.Windows.Forms.RichTextBox displayTextBox;
private System.Windows.Forms.Label dieLabel1; :
private System.Windows.Forms.Label dieLabel12; 33
1 // RollDie2Form.cs: Rolling 12 dice with frequency chart.
12 // displays the different dice and frequency information
13 public partial class RollDie2Form : Form {
private Random randomNumber = new Random();
private int ones, twos, threes, fours, fives, sixes;
public RollDie2Form() {
InitializeComponent();
ones = twos = threes = fours = fives = sixes = 0;
42 }
Sets all of the variables to 0

28. 46 // simulates roll by calling DisplayDie for each label and displaying the results
protected void rollButton_Click( object sender, System.EventArgs e ) {
// pass labels to a method that randomly assigns a face to die
DisplayDie( dieLabel1 ); :
DisplayDie( dieLabel12 );
double total = ones + twos + threes + fours + fives + sixes; 67
Pass the label to be assigned a random number

29. 68 // 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 ) + "%";
} // end rollButton_Click 84
// display the current die, and modify frequency values
public void DisplayDie( Label dieLabel ) {
int face = 1 + randomNumber.Next( 6 );
dieLabel.Image = Image.FromFile(
Directory.GetCurrentDirectory() + "\\images\\die" + face + ".gif“ );
Assign a random face to the label based on the number generated

30. 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;
case 2: twos++;
break;
case 3: threes++;
break;
case 4: fours++;
break;
case 5: fives++;
break;
case 6: sixes++;
break;
} // end switch
} // end DisplayDie
A switch statement is used to keep track of number of each die rolled

31. 12 labels
A button with a click event
DisplayTextBox

32. Example: Game of Chance
GUI controls
GroupBox
Holds other controls
Manages and organizes them
PictureBox
Used to display a picture on the form

33. 29 // declare other variables 30 int myPoint; 31 int myDie1;
private System.ComponentModel.Container components = null; 15
private System.Windows.Forms.PictureBox imgPointDie1;
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.GroupBox fraPoint;
1 // CrapsGameForm.cs
12 public partial class CrapsGameForm : Form
13 { 28
// declare other variables
int myPoint;
int myDie1;
int myDie2; 33
Global variables

34. 34 public enum DiceNames 35 { 36 SNAKE_EYES = 2, 37 TREY = 3,{
SNAKE_EYES = 2,
TREY = 3,
CRAPS = 7,
YO_LEVEN = 11,
BOX_CARS = 12, }
// 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
When the second rolled sum equals the first rolled sum the player wins

35. 63 else 64 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
Casting enum type to an int using explicit conversion

36. 104 displayDie( imgPointDie2, myDie2 );
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;
} // end switch
} // end playButton_Click
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

37. 126 die1 = randomNumber.Next( 1, 7 );
// 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
Generates two random numbers, one for each die

38. CrapsGame.cs Program Output

39. Duration of Identifiers
The amount of time an identifier exists in memory
Local variables of a method
Automatic duration: Created when declared and destroyed when the block exits
Not initialized
Instance variables of a class
Initialized by compiler, if not done by programmer
Most variables are set to 0, false or null

40. Scope Rules Scope Class scope Block 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
Repeated names causes previous to be hidden until scope ends
Block scope
From when created until end of block (})
Only used within that block
Cannot repeat variable names

41. Will output the value of 5
2 // A Scoping example.
11 private System.ComponentModel.Container components = null;
private System.Windows.Forms.Label outputLabel;
public partial class Scoping : Form {
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; }
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

42. 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"; }
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"; }
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

43. Scoping.cs Program Output

44. Recursion
Same as C++

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

46. 21 // call both versions of Square 22 outputLabel.Text =
private System.ComponentModel.Container components = null;
private System.Windows.Forms.Label outputLabel;
1 // MethodOverloadForm.cs
11 public partial class MethodOverloadForm : Form
12 { 16
public MethodOverloadForm() {
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 ); }
Two versions of the square method are called

47. 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; }
One method takes an int as parameters
MethodOverload.cs Program Output
The other version of the method uses a double instead of an integer

48. MethodOverload2.cs Program Output
1 // Overloaded methods with identical signatures and different return types. 6
7 class MethodOverload2
8 {
9 public int Square( double x ) {
return x * x; } 13
// second Square method takes same number, order and type of arguments, error
16 public double Square( double y ) {
return y * y; }
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