How To Code in C#

Programming in C#
David Ringsell MCPD MCT MCAD
David Ringsell MCSD

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Course Content
Unit Topic
1. Getting Started with C#
2. C# Language Fundamentals
3. Branching
4. Operators
5. Object-Orientated Programming
6. Classes and Objects
7. Inside Methods
8. Debugging
9. Inheritance and Polymorphism
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Course Content 2
Unit Topic
10. Operator Overloading
11. Structs
12. Interfaces
13. Arrays
14. Collection Interfaces and Types
15. Strings
16. Throwing and Catching Exceptions
17. Delegates and Events
18. Generics
19. New Language Features
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Your Consultant
 David Ringsell MCPD MCPD MCT
 Trainer, developer, consultant
 Develops in C#.Net, VB.Net, ASP.Net and
Sequel Server
 More courses and tutorials: www.talk-it.biz
 david@talk-it.biz

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References
 Learning C# by J. Liberty from O‟Reilly
 C# 2010 Professional from Wrox

6

 Why C# and not VB
 The C# Programming Language
 C# Goals
 How C# Fits with .Net
 Overview of the .NET Framework

7

Why C# and not VB
 Syntax more like C++ and Java
 Syntax very concise
 Designed for object orientation
 Started with a clean slate
 Everything is an object

 Microsoft are evolving language

8

C# Supports ….

 Structured
 Procedural, blocked
 Object-orientated
 Classes, methods, properties
 Event driven
 Event handlers, delegates

… programming
9

C# Goals
 Safe
 Find bugs early in development process
 Simple
 Few keywords
 Internet Centric
 Designed for developing web programs
 Hi Performance
 Designed for industrial strength programming

10

How C# Fits with .Net
 Languages
 VB.Net, C#, C++ …
 Visual Studio Integrated Development Environment (IDE)
 Framework Class Libraries (FCL)
 ADO, ASP, XML, …
 Common Language Runtime (CLR)
 Windows Operating System

11

Overview of .Net
Visual
Basic C++ C# Perl J# …

XML Web Services User Interface
ASP.NET

ADO.NET: Data and XML

.NET Framework Class Library

Common Language Runtime

COM+
Message
(Transactions, Partitions, IIS WMI
Queuing
Object Pooling)

Win32
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 Data Types
 Numeric Types
 Non-Numeric Types: char and bool
 Variables
 Definite Assignment
 Constants
 Strings
 Statements

13

Data Types
 Common C# intrinsic Type Size in Bytes
data types
byte 1
bool 2
int 4
long 8
float 4
double 8
decimal 12
14

Typing in C#
 C# is a strongly typed language
 Types come in two flavours
 Value (intrinsic)
 Reference (classes …)

 Each type has a name (int) and size (4b)
 The .Net equivalents for int is Int32

15

Numeric Data Types
 Unsigned (positive)
 byte, ushort, uint, ulong
 Signed (positive or negative)
 short, int, long, float, decimal, double
 Select the smallest type that will hold the
required range of numbers

16

Non-Numeric Types: char and bool
 char
 Holdsjust a single character
 Can hold:
 Simple character („A‟)
 Unicode character (u0041)

 Escape character („n‟)

 bool
 Holds true or false in one byte

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Declaring Local Variables

int myInt;
System.Console.WriteLine("Uninitialized, myInt: {0}",myInt);

myInt = 5;
int mySecondInt = 10; // declare and initialise
int myInt4,myInt5; // declare multiple variables

What is the value on an integer
before it is initialised?

18

Declaring Constants

const int FreezingPoint = 32; // degrees Farenheit
const int BoilingPoint = 212;

Why would you create
constants?

19

Declaring Enumerations
An enumeration is a set of named constants

// declare the enumeration
The data type defaults
enum Temperatures:int
to int
{
WickedCold = 0,
FreezingPoint = 32,
LightJacketWeather = 60,
SwimmingWeather = 72, Why would you create
BoilingPoint = 212, enumerations?
}
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Using Enumerations

System.Console.WriteLine("Freezing point of water: {0}",
(int) Temperatures.FreezingPoint );
System.Console.WriteLine("Boiling point of water: {0}",
(int) Temperatures.BoilingPoint );

21

Declaring Strings

A string is an object

string myString = “Hello World” ;// declare and initialise string

Where would you use strings
in your code?

22

Statements, Expressions & White
Space
 A statement ends in a semicolon
int myInt = 23;
 An expression can be part of an assignment
myInt = myInt * 23;
 White spaces are ignored
myInt = myInt * 100;

23

Unit 2 Lab
To write statements that prompt and greet the user
1. Open Visual Studio.Net and create a new C# Console Application
project
2. In the Main method insert the following line:
string myName;
3. Write a statement that prompts users for their name.
4. Write another statement that reads the user‟s response from the
keyboard and assigns it to the myName string.
5. Add one more statement that prints “Hello myName” to the screen
(where myName is the name the user typed in).
6. Save your work.

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Unit 2 Lab …
When completed, the Main method should contain the following:

static void Main( )
{
string myName;
Console.WriteLine("Please enter your name");
myName = Console.ReadLine( );
Console.WriteLine("Hello {0}", myName);
}

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3. Branching
 A method is a mini program
 The statements in it executed from top to bottom
 Branching temporarily halts this execution to call
another method or statement
 There are 2 types of branching
 Conditional
 Unconditional

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Ways of Branching
 Call a method
 Temporally transfer control to the called method
 Looping
 Repeat statements (conditionally or unconditionally)
 If Statements
 Execute statements only if condition true
 Switch Statements
 Execute statements depending on value of variable

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Calling Methods
Main
Statement1
Method A
Statement2 Call
Statement1
MethodA()
Statement2
Statement3
MethodB()
Statement4 Call
Statement3 Method B
End method
Statement4
Statement1
Return End method
Statement2
Statement3
Statement4
Return
End method
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Branching to a Method

static void Main()
{
Console.WriteLine("In Main! Calling SomeMethod()...");
SomeMethod();
Console.WriteLine("Back in Main().");

}
static void SomeMethod()
{
Console.WriteLine("Greetings from SomeMethod!");
}

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If Statements
Condition (always in brackets)

int valueOne = 10;
int valueTwo = 20;

if ( valueOne > valueTwo )
{
Console.WriteLine("ValueOne: {0} larger than ValueTwo: {1}",
valueOne, valueTwo);
}

Statement

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Multiple Statement Block

if ( valueOne >= valueThree ) // true?
{
Console.WriteLine( "valueOne: {0} larger or equal to
valueThree: {1}", valueOne, valueThree);
Console.WriteLine("Good thing you tested again!");
}

Braces create
block

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If … else Statements
Execute if condition
true
if ( valueOne > valueTwo )
{
Console.WriteLine(
"ValueOne: {0} larger than ValueTwo: {1}",
valueOne, valueTwo);
} // end if
else
{
Console.WriteLine(
"Nope, ValueOne: {0} is NOT larger than valueTwo:
{1}",valueOne, valueTwo);
} // end else

Execute if condition
false

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Nested if Statements
Outer if
if (temp <= 32) statement
{
Console.WriteLine("Warning! Ice on road!");
if (temp == 32) Nested if statement
Console.WriteLine( "Temp exactly freezing, beware of water.");
}
else
{
Console.WriteLine("Watch for black ice! Temp: {0}", temp);
}

Quiz: Are there a
missing braces?

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Switch Statements
switch on the value of
myChoice

switch (myChoice)
{
case Democrat:
Console.WriteLine("You voted Democratic.");
break;
case Republican:
Console.WriteLine("You voted Republican.");
break;
case Progressive: Break out!
Console.WriteLine("You voted Progressive.");
break;
}

Execute case statements
depending on value
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The Default Case
switch (myChoice)
{
case Democrat:
Console.WriteLine("You voted Democratic.n");
break;
case Republican:
Console.WriteLine("You voted Republican.n");
break;
case Progressive:
Console.WriteLine("You voted Progressive.n");
break;
default:
Console.WriteLine("You did not make a valid choice.");
break;
}

When will the default
statements be executed?
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Falling Through and Jumping Cases

case "NewLeft":
Console.WriteLine(
"The NewLeft members are voting Democratic.");
goto case "Democrat";
Jump Case
case "Democrat":
Console.WriteLine("You voted Democratic.n");
break;
case "CompassionateRepublican":
case "Republican":
Console.WriteLine("You voted Republican.n");
Console.WriteLine("Don't you feel compassionate?");
break;

Fall through case
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Looping Statements
 Execute statements repeatedly
 The number of time can depend on condition
 Types of loop
 Use goto statement
 Use while loop
 Use for loop

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Creating Loops with goto

int counterVariable = -10; The label
repeat:
Console.WriteLine("counterVariable: {0}",counterVariable);

++counterVariable; Increment the
counter
if (counterVariable < 30) goto repeat;

Branch to label
Why is this type of loop
not a good idea?
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The while Loop
While the condition is true …

while (counterVariable < 10)
{
Console.WriteLine("counterVariable: 0}",counterVariable);
counterVariable++;
}
… execute the
statements

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The do … while Loop

do
{
Console.WriteLine("counterVariable:{0}",counterVariable);
counterVariable--;
} The condition is now
after the statements
while (counterVariable >0);

What is the minimum
number of times the
statements will run?
40

The for Loop
The counter variable changes on
each iteration

for (int counter=100; counter>80; counter--)
{
Console.WriteLine( "counter: {0} ", counter);
}

What numbers will be
output?

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Break Out!
for (int counter=0; counter<10; counter++)
{
Console.WriteLine("counter: {0} ", counter);

if (counter == 5)
{
Console.WriteLine("Breaking out of the loop");
break;
}
}

If condition is
What is the next met, break out
statement executed
after a break out?
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Continue a Loop from the Top

if (signal == "0")
{continue;}

Start loop from top at next
iteration

Can you think of an
example where this be
used?

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Other Loops
for ( ; counter<10; counter++) No initialisation

for (int counter = 0; counter<10; ) No increment

for ( ;; ) No anything!

while (true) Always true
(loop forever?)

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Unit 3 Lab
1. To write statements to input two numbers and display the result

2. To write if …else statements to input three numbers and display the largest

3. To write switch statements to input a country and display its capital

4. To write looping statements that to display the list 10, 20, 30, 40 … 100

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4. Operators
 A symbol that takes an action
 Assignment (=)
 Mathematical ( +, -, *, / )
 Increment and Decrement ( +=, -= )
 Relational ( >, >=, <, <=)
 Logical ( &&, ||, ! )

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Assignment Operators (=)
Declare and assign
int smallInt = 5;

smallInt = otherInt= 5;
Multiple Assignments

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Mathematical Operators
+ Add

- Subtract

* Multiply

/ Divide

% Modulus
What is the order of
precedence of
these operators?
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The Modulus Operator (%)
for (int counter=1; counter<=100; counter++)
{
Console.Write("{0} ", counter);
If the remainder after
if ( counter % 10 == 0 ) dividing by 10 is 0
{
Console.WriteLine("t{0}", counter);
}
}

What will be
output?
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Calculate and Reassign Operators
MySalary += 5000 Add 5000 to MySalary
MySalary -= 5000 Subtract 5000 from MySalary
MySalary *= 5000 Multiply MySalary by 5000
MySalary /= 5000 Divide MySalary by 5000

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Increment and Decrement by 1
++ intB; Increment
-- intB; Decrement
intA = ++ intB; Increment then assign - prefix
intA = -- intB; Decrement then assign - prefix
intA = intB ++; Assign then increment - postfix
intA = intB --; Assign then decrement - postfix

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Prefix and Postfix Operators
Increment then
int original = 10; assign
int result;

result = ++original;
Console.WriteLine("After prefix: {0}, {1}", original,result);

result = original++;
Console.WriteLine("After postfix: {0}, {1}",original,result);

Assign then
increment
What numbers are
output?
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Relational Operators
intA = 100; intB = 50;
intA == 100 Equals true
intA != 100 Not equals false
intA > intB Greater than true
intA >= intB Greater than or equal to true
intA < intB Less than false
intA <= intB Less than or equal to false
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Logical Operators
x = 5; y = 7;

Name Operator Statement Result

And && (x==3) && (y == 7) False

Or || (x==3) || (y == 7) True

Not ! !(x==3) True

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The Conditional Operator (?)
Condition

int maxValue = valueOne > valueTwo ? valueOne : valueTwo;

Assign valueOne if true Assign valueTwo if false

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Operator Precedence
intA = 5+7*3;
What‟s the
intA = (5+7)*3; results?

Category Operators
1- Unary +-!()
2- Multiplicative */%
3- Additive +-
4- Relational < > <= <=
5- Logical && ||
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Unit 4 Lab
1. To write statements using the multiplication operator to display
the twelve-times table

2. To write statements to input two numbers and use logical
operators to output if the result of multiplying them will be positive
or negative

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 What is OOP?
 Creating Models
 Classes and Objects
 Defining a Class
 Class Relationships
 The Three Pillars of OOP
 Analysis and Design

58

What is OOP?
 Windows and web programs are vastly complex
 Richgraphical interfaces
 Complex business relationships
 Users interact with programs in many ways

 Programmers refer to information about the problem
they are solving as the problem domain
 OOP is a technique for managing this complexity by
defining objects from the problem domain

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Characteristics of Objects
 State
 The current conditions of an object, e.g. a customer
object‟s state may include address & phone number.
 Capabilities
 Whatthe object can do that is relevant to the problem
domain, e.g. buy an item, return an item …
 Responsibilities
 The customer object is responsible for managing its own
address. No other object needs to know this.

60

Creating Models
 Humans are model builders
 Models are simplifications e.g. a road
atlas
 Good models hold information that is
relevant to the problem domain, no
more & no less
 Programming models contain
metaphors to represent concepts,
E.g. a window, a folder
 A good OO design is an accurate
model of the problem
61

Classes and Objects
 A class defines a new type of thing, e.g. a
car class
 A class defines the common characteristics,
e.g. every car has wheels, brakes …
 An object is an individual instance of a
class, e.g. a specific car object
 An object is just a thing

62

Defining a Class
 A class definition contains members
 These describe the characteristics and
behaviour of objects of the classes type
 These members can be
 Fields & Properties
 These hold the internal state of the object
 Methods
 These do the work for the object

63

Defining a Class
Class
public class Cat definition
{
private int weight; Fields
private String name;

public Cat(String name, int weight)
{
this.name = name;
this.weight = weight;
}
// Class code … A method
}

64

Class Relationships
 Good OO design depends on
establishing relationships among classes
 Classes interact and relate in various
ways
 The simplest form of interaction is when a
method in one class calls a method in
another
 Some complicated classes are composed
of other classes, e.g. an automobile is
composed of wheels, an engine … Car
 The automobile class is said to aggregate
the simpler classes Engine Wheels

Gear Box Piston
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The Three Pillars of OOP
 Good OO design is built on three sturdy pillars
 Each class is fully encapsulated to define its state
 Inheritance allows the definition of a hierarchical
relationship among classes
 Polymorphism allows a group of objects to be
treated in the same way

66

Encapsulation
 Each class is discreet and self-contained
 The implementation of one class can be
changed without affecting other classes
 There is a clear separation between a classes:
 Public interface (its contract with clients)
 Private implementation (how it does what it has
agreed)

67

Inheritance
 Inheritance allows a new class to be Stringed
Instrument
derived from an existing class
 The new (derived) class inherits
characteristics from the existing
(base) class Violin

 The inheritance relationship is Violin is derived from a base
referred to as an is-a relationship class

e.g. a violin is a stringed instrument
 Inheritance allow the creation of a
family of objects, e.g. a button is a
control, but also a list box is a
control
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Polymorphism
 Poly (many) – Morph (forms)
 Consider the controls class, that has derived
classes; buttons & list boxes
 These subclasses inherit a shared ability; the draw
method
 The draw method can be called for each subclass
 Each subclass knows how to implement the method
for itself (draw a button, draw a list box)

69

Analysis and Design
 Analysis is researching the problem
 Design is actually planning the solution
 Analysis can take week or months for complex
problems
 Analysis includes
 Determining the success factors
 Specifying the requirements (functional spec.)
 Design Includes
 Imagining the classes and their inter-relationship
 Creating class diagrams using UML
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 First ask what does the class model
 Can I inherit from an existing base class
 What members does the class expose
 An object is an instance of a class
 Classes are reference types held on the stack
in memory

71

A Simple Class
public class MyClass
{
public void SomeMethod(int firstParam, float secondParam)
{
Console.WriteLine(
"Here are the parameters received: {0}, {1}", firstParam,
secondParam);
}
}
public class Tester
{
static void Main()
{
int howManyPeople = 6;
float pi = 3.14f;
MyClass mc = new MyClass();
mc.SomeMethod(howManyPeople, pi);
}
} 72

Creating a Constructor
 A constructor
 Creates an instance of a class
 Puts this in a valid state
 The compiler will implicitly provide (if not declared)
 Can provide with arguments
 Can provide several overloaded versions of
constructor
 Has same name as class & no return type

73

Creating a Constructor
public class Time
{
// private member variables
int hour;
int minute;
int second;

// public method
public void DisplayCurrentTime()
{
System.Console.WriteLine("{0}/{1}/{2}", hour, minute, second);
}

// constructor
public Time(int theHour, int theMinute, int theSecond)
{
hour = theHour;
minute = theMinute;
second = theSecond;
}
}
74

Others Clever Things with Objects
 Initializer
 Initialize the value of a class member variable
int second = 30

 The this keyword
 Refers to the current instance of an object
Public void SomeMethod(int hour)
{
this.hour=hour
}

75

Access Modifiers
 Determines availability of the class to clients
 public: visible to any client class
 protected: visible only to derived classes
 internal: visible only to classes in the same
assembly

[access-modifiers] class <identifier> [:base]
{ class body }

76

Instance and Static Members
 Instance Members
 Associated with instance of class
 btnUpdate = new Button();
 btnUpdate.Draw();

 Static Members
 Associated with class itself
 Button.GetButtonCount();

77

Instance and Static Members
public class Cat
{
private static int instances = 0;
private int weight;
private String name;

public Cat(String name, int weight)
{
instances++;
this.name = name;
this.weight = weight;
}

public static void HowManyCats()
{
Console.WriteLine("{0} cats adopted", instances);
}

public void TellWeight()
{
Console.WriteLine("{0} is {1} pounds", name, weight);
}
78
}

Destroying Objects
 Objects are destroyed by Garbage Collector
 To free unmanaged resources declare a
destructor (will be called by Garbage Collector)
 ~MyClass(){}
 Or, provide a Dispose() method & ask clients to
call
 protected override void Dispose( bool
disposing )

79

Encapsulating Data with Properties
Declare a property that
can be read from or
public int GetHour written to
get
{
return Hour;
}
set
{
Hour =value;
}

80

Unit 6 Lab
1. To write statements to define a class called Date that has a
constructor and fields for year, month, day. Also define a method
called DisplayTime() in the class.

2. To add an overloaded constructor to the Date class

3. To add properties (get & set) for the year, month, day to the Date
class

81

7. Inside Methods
 Several methods can have the same name
 Overload method signature
 Class data can be encapsulated with
properties
 Provide clients controlled access to class state
 Method can return multiple values by passing
parameters by reference

82

Overloading Method Signatures
Same method name
public Time(System.DateTime dt)
{ … } but a different number
& type of parameters
public Time(int Year, int Month, int Date,
int Hour, int Minute, int Second)
{ … }

public Time(int Year, int Month, int Date,
int Hour, int Minute)
{ … }

83

Passing Parameters by Reference
Declare a method that
takes parameters
passed by reference

public void GetTime(ref int h, ref int m, ref int s)
{
h = Hour;
m = Minute; Now call the method
s = Second; with reference
} parameters

t.GetTime(ref theHour, ref theMinute, ref theSecond);

84

Creating a Two Tier Application
 Create the business tier
Create a new class library project
Create a class to represent a business entity, say Date
Add properties that expose attributes, say year, month, day
Add methods for business rules
 Create the presentation tier
Create a new console application project
Add a reference to the above class library project
Create an object from class
Use the object‟s properties to access data items
Use the object‟s methods to perform business processes

85

Unit 7 Lab
To add a GetDate method to the Date class, using ref
parameters for year, month, day. Test the method.

86

8. Debugging
 A powerful tool to understand and fix code at
runtime
 Setting a breakpoint
 Stepping through code
 Using the debug windows view variables
 The call stack

87

Setting a Breakpoint

Click here to set Code is paused at runtime
breakpoint

88

Stepping through Code
 Step into (F11)
 Execute the current line of code
 Step over (F10)
 Execute the current line of code, but skip procedures
 Step out (Shift F11)
 Resume execution from calling procedure
 The values of variables can be seen by hovering
mouse pointer over them

89

Using the Debug Windows
 Immediate Window
 Evaluates expressions, executes statements, print variable
values
 Locals Window
 View ( and modify) variables within local scope
 Watch window
 Add variables to watch their values
 Call Stack
 Show the calling methods of the current method

90

9. Inheritance
 Derived classes are defined from a base class
 The derived class specialises the base class
 The derived class inherits all members
 The derived class can also implement its own
version of the base class

91

Inheritance Hierarchy

Window

… inherits from … Button ListBox

CheckBox Command

RadioButton

93

Implementing Inheritance
 Define Base Class
public class BaseForm : System.Windows.Forms.Form

 Define Derived Class
public class AddressForm : BaseForm

 Use Derived Class in Client Class
AddressForm af = new AddressForm();
af.Show();

94

Inside Inheritance
 Calling the Base Class Constructor
public AddressForm():base()
 Replacing Base Methods
protected new void OnCustomerLocate()
 Calling Base Methods
base.OnCustomerLocate

95

Polymorphism
 Powerful aspect of inheritance
 Poly (many) – Morph (forms)
 Example: T-Mobile supplies many handsets
 Each handset “instance” knows how to ring
 When the ring command is sent, the handset
obeys in its own way

96

Creating a Polymorphic Method
 In Base
public class Window
public virtual void DrawWindow()
 In Derived Class
public class ListBox : Window
public override void DrawWindow()

97

Calling the Polymorphic Method
 In Client Class
Window[] winArray = new Window[2];
winArray[0] = new Window();
winArray[1] = new ListBox();

//Loop thru array calling polymorphic method
for (int i = 0;i < 2; i++)
{
winArray[i].DrawWindow();
}

98

Other Kinds of Methods
 The derived class must implement a base
method
abstract public virtual void DrawWindow()

 The derived class cannot override a base
method
sealed public virtual void DrawWindow()

99

Unit 9 Lab
To define a class called Control, with a constructor and a
DrawControl() method. Create a class called TextBox
that inherits from Control and replaces the DrawControl
method. Test the TextBox class

100

 What is Operator Overloading
 Using the Operator Keyword
 Creating Useful Operators
 The Equals Operator
 Conversion Operators

101

What is Operator Overloading
 C# allows new classes to have the
functionality of built-in types
 This includes the ability to define operators for
a new class
 For example: + and = operators may be
defined for a Fraction class
 This is a better alternative to creating a
Fraction.Add() method
102

Using the operator Keyword
 C# operators are static methods
 To create a new operator combine the
operator keyword with the symbol
 This operator (+) will take two parameters of
type Fraction & return a Fraction

public static Fraction operator+(Fraction lhs, Fraction rhs)

103

Defining an Operator
Create the
public Fraction(int numerator, int denominator) Fraction class
{
this.numerator=numerator;
this.denominator=denominator;
}
Create the +
public static Fraction operator+(Fraction lhs, Fraction rhs) operator
{
if (lhs.denominator == rhs.denominator)
{
return new Fraction(lhs.numerator+rhs.numerator, lhs.denominator);
}
int firstProduct = lhs.numerator * rhs.denominator;
int secondProduct = rhs.numerator * lhs.denominator;
return new Fraction(
firstProduct + secondProduct,lhs.denominator * rhs.denominator
);
}

104

Creating Useful Operators
 Operator overloading can make code more
intuitive when new classes behave like built in
types
 But, resist the temptation to overuse
 For example: the incremental operator (++)
could cause a pay increase to an Employee
class
 This may be confusing to clients of this class

105

The Equals Operator
 The root Object class offers an Equals()
method
 If the equals operator (==) is overridden for a
Fraction, it is recommended that the Equals()
method is also overridden
 This means that Equals() can be called on two
objects Fractions

106

Overloading the Equals Method
Test if the
public override bool Equals(object o) parameter is an
{ object
if (! (o is Fraction) )
{
return false;
}
return this == (Fraction) o;
}
Use the
overloaded ==
to test for
equality

107

Overloading the == and != Operators
public static bool operator==(Fraction lhs, Fraction rhs)
{
if (lhs.denominator == rhs.denominator && Test for
lhs.numerator == rhs.numerator) equality of
{ Fractions
return true;
}
return false;
}

public static bool operator!=(Fraction lhs, Fraction rhs)
{
return !(lhs==rhs); Test for inequality by
} delegating to the ==
Why is it a good idea operator
to create both the ==
& != operators? 108

Using the == and != Operators

Test for equality
if (f4 == f3)
{
Console.WriteLine("f4: {0} == F3: {1}",
f4.ToString(),
f3.ToString());
}
if (f4 != f2) Test for inequality
{
Console.WriteLine("f4: {0} != F2: {1}",
f4.ToString(),
f2.ToString());
}

Where is the ToString()
method implemented?
109

Conversion Operators
 An int data type can be implicitly converted to a
long
 Also, a long data type can be explicitly
converted to an int
 Similarly, operators can be defined for the
Fraction class to convert from:
a Fraction to an integer e.g. 9/4 becomes 2
 an integer to a Fraction e.g. 15 becomes 15/1

110

Creating Conversion Operators
public Fraction(int wholeNumber) Constructor taking
{ a whole number
numerator = wholeNumber;
denominator = 1;
}

public static implicit operator Fraction(int theInt) Implicitly
{ converting int
return new Fraction(theInt); to fraction
}

public static explicit operator int(Fraction theFraction)
{
return theFraction.numerator /theFraction.denominator;
}
Explicitly
converting
Fraction to int 111

Using Conversion Operators

Fraction f1 = new Fraction(3,4);
Fraction f2 = new Fraction(2,4);
Fraction f3 = f1 + f2;

Fraction f4 = f3 + 5; Convert int to fraction implicitly
int truncated = (int) f4;
Convert fraction to int explicitly

112

Unit 10 Lab
To define a class called Fraction, with a constructor and a ToString()
method. Create a subtraction operator (-) using operator
overloading. Test the operator.

113

11. Structs
 Lightweight alternative to classes
 Like classes they can define
 Constructors, properties, methods and fields
 But they do not allow
 Inheritance or destructors
 They are value not reference types
 Use for small, simple objects

114

Defining a Struct
public struct Location
{ The struct has
private int xVal; private data
private int yVal;

public Location(int xCoordinate, int yCoordinate)
{
xVal = xCoordinate;
It has a
yVal = yCoordinate;
constructor
}

115

Defining a Struct 2
public int XVal
{
get { return xVal; }
set { xVal = value;} The struct has two
} properties …

public int YVal
{
get { return yVal; }
set { yVal = value; }
} … and a method

public override string ToString()
{
return (String.Format("{0}, {1}", xVal,yVal));
}
} // end struct
116

Using a Struct
Create an instance of the struct
Location loc1 = new Location(200,300);

Display the values in the struct
Console.WriteLine("Loc1 location: {0}", loc1);

Invoke the default constructor
Location loc2 = new Location();
Console.WriteLine("Loc2 location: {0}", loc2);

myFunc(loc1); Pass the struct to a method

What is output when
the default
constructor is used?
117

Unit 11 Lab
To define a struct called Colour, with a constructor and a ToString()
method. This will hold three numbers to represent the red, green
and blue component of the colour. Test the Struct.

118

12. Interfaces
 Implementing an Interface
 Implementing More Than One Interface
 Casting to an Interface
 The is and as Operators
 Extending Interfaces
 Combining Interfaces

119

What is an Interface
 Allows the designer to specify the behaviours
an object must implement
 The interface describes only which properties,
methods and events will exist
 The class using the interface agrees to
implement all of these

120

Implementing an Interface
Define the interface

interface IStorable
{
void Read();
void Write(object obj);
int Status { get; set; }
}

Define its properties
and methods
121

Create a Class to Implement the Interface
public class Document : IStorable
{
public void Read() Implement the Read
{ method
Console.WriteLine(
"Implementing the Read Method for IStorable");
}
public void Write(object o) Implement the Write
{ method
Console.WriteLine(
"Implementing the Write Method for IStorable");
}
public int Status Implement the
{ Status property
get{ return status; }
set{ status = value; }
}
122

Test the Implementing Class
Document doc = new Document("Test Document");
doc.Status = -1;
doc.Read();
Console.WriteLine("Document Status: {0}", doc.Status);

Use the interface‟s
methods and
property

123

Implementing More Than One
Interface
 Classes can derive from only one base class
 But, classes can implement any number of
interfaces
 This provides added flexibility for class
designers

124

Implementing Two Interfaces
interface IStorable
{
void Read();
void Write(object obj);
int Status { get; set; } Here's the
} new interface
interface ICompressible
{
void Compress();
void Decompress(); Document
}
implements both
interfaces

public class Document : IStorable, ICompressible

125

Casting to an Interface
 In some cases you don‟t know the type of the class
 You only know the interface it implements
 You can then cast the object to that interface type
 You can then use the object‟s members through the
interface type
 Access through an interface allows you to treat the
interface polymorphically

126

Casting to an Interface 2
public class Document : IStorable
The Document
class Implements
the IStorable
interface

IStorable isDoc = (IStorable) doc;
isDoc.Read();
Cast the doc
What happens if the object to the
class does not IStorable type
implement the
interface? 127

The is Operator
Does the object
Document doc = new Document("Test Document"); implement
interface?
if (doc is IStorable)
{
IStorable isDoc = (IStorable) doc;
isDoc.Read();
}
else
Only cast if
{ does
Console.WriteLine("Could not cast to IStorable");
}

128

The as Operator
 This combines the is evaluation and the cast
operation
 If the cast is not valid the operator returns null
 The as operator is more efficient than the is
operator

129

The as Operator 2

IStorable isDoc = doc as IStorable;
if (isDoc != null)
{
Cast using as, then
isDoc.Read(); test for null
}
else
{
Console.WriteLine("Could not cast to IStorable");
}

130

Extending Interfaces
 Add new members
 Modify how existing members work
 For example
 Extend ICompressible with the new interface
ILoggedCompressible
 Add one additional method to
ILoggedCompressible

131

Extending Interfaces 2
interface ICompressible Define ICompressible
{ interface
void Compress();
void Decompress();
}
interface ILoggedCompressible : ICompressible Extend ICompressible to
{ log the bytes saved
void LogSavedBytes();
}

Document implements
public class Document : ILoggedCompressible ILoggedCompressible

Now implement
public void LogSavedBytes()
{ that extra method
Console.WriteLine("Implementing LogSavedBytes");
}
132

Combining Interfaces
 New interfaces can be created by adding
existing interfaces
 New members can be added to the new
interface

133

Combining Interfaces 2
Add two existing interfaces
interface IStorableCompressible : IStorable, ILoggedCompressible
{
void LogOriginalSize();
}
Add method

public class Document : IStorableCompressible

Class that will
implement the
interface
134

Unit 12 Lab
To define an interface called IClient. This includes properties
for name and address details and a method called Order.
Create a class called Customer that implements the interface
and adds an additional method. Test the Customer class.

135

13. Arrays
An array is a collection of objects of the same type
 Declaring Arrays
 Accessing Array Element
 The foreach Statement
 Multidimensional Arrays
 System.Array
 Indexers

136

A One Dimensional Array
0 1 2 3 4 5 6 7

Like a set of
pigeon holes
Each pigeon hole
can hold the same
kind of object
Each pigeon hole
is accessed by its
number: 0, 1, 2
… 137

Declaring Arrays
Declare arrays

int[] intArray;
Employee[] empArray;

intArray = new int[5];
empArray = new Employee[3];

What are the default
values of the array Initialise arrays with 5
elements? & 3 elements
138

Declaring Arrays 2
Declare and
initialise arrays
int[] intArray = new int[5];
Employee[] empArray = new Employee[3];

The default values for Alternatively, declare,
integers are 0, and for objects
initialise and
null
populate arrays
int[] intArray = { 2, 4, 6, 8, 10 };
Employee[] empArray =
{ new Employee(5), new Employee(7), new Employee(9) };

139

Accessing Array Elements
This returns the 4th element since
indexing starts at 0
intArray[3];
Populate the Employee array
using a loop

for (int i = 0;i<empArray.Length;i++)
{
empArray[i] = new Employee(i+5);
Console.WriteLine(empArray[i].empID);
}

140

The foreach Statement
Loop through all items in the
array

foreach( int theInt in intArray )
{
Console.WriteLine(theInt.ToString());
}

141

The params keyword
The method takes a variable
number of integers
as a parameter
public void DisplayVals(params int[] intVals)
{
foreach (int i in intVals)
{
Console.WriteLine("DisplayVals {0}",i);
}
}

int [] explicitArray = new int[4] {5,6,7,8};
DisplayVals(explicitArray);
Call method passing
an array
142

Multidimensional Arrays
Col. 0 Col. 7

Row 1

Row 2

3,2
Row 3

Row 4

Row 5

143

Declaring 2D Arrays
Declare the array

int[,] boxArray = new int[2,3];

int[,] rectangularArray =
{
{0,1,2}, {3,4,5}, {6,7,8}, {9,10,11}
};

Or declare and populate
the array

144

Loop through 2D Array

Outer loop
for (int i = 0;i < rows;i++)
{
for (int j = 0;j<columns;j++) Inner loop
{
Console.WriteLine("rectangularArray[{0},{1}] = {2}",
i,j,rectangularArray[i,j]);
}
}
Which is iterated through
first, the rows or the
columns?
145

Jagged Arrays (Array of Arrays)
int[][] jaggedArray = new int[rows][]; Declare the rows of
various lengths
jaggedArray[0] = new int[3];

Fill some elements
jaggedArray[0][3] = 15;

146

System.Array Class
 Arrays are implemented
with the System.Array class,
which provides these useful
methods:
 Clear()
 Copy()
 Reverse()
 Sort()
 Length()
 Rank()

147

Indexing Classes
 Some classes can act like arrays
 For example, a class list ListBoxTest can act
like an array of the strings it contains
 An indexer allows a class to be treated like an
array:
ListBoxTest[3];

148

Indexing Classes
public class ListBoxTest
{ Allow array-like access
public string this[int index]
{
get
{
if (index < 0 || index >= strings.Length)
{
// handle bad index
Get value from
}
internal array
return strings[index];
}
set
{ Set value in
strings[index] = value; internal array
}
} 149

Testing an Indexed Class
// create a new listbox and initialize
ListBoxTest lbt = new ListBoxTest("Hello", "World");

// add a few strings
lbt[1] = “Who”
lbt[2] = “are";
lbt[3] = “the";
lbt[4] = “developers";

// access all the strings
for (int i = 0; i<lbt.GetNumEntries(); i++)
{
Console.WriteLine("lbt[{0}]: {1}",i,lbt[i]);
}

150

Unit 13 Lab
To create a two dimensional array of integers holding the twelve-
times table. Use looping statements to populate the array and
display its elements

151


 The Collection Interfaces
 Array Lists
 Queues
 Stacks

152

What Are Collections?
 A collection holds a group of similar objects
 An array is the simplest type of collection
 The .Net Framework provides built-in collection types
 The .Net Framework holds collection classes in
 System.Collections

 Each type provides standard methods for accessing
& manipulating the collection‟s content

153

The Collection Interfaces
 Collections implement interfaces that provide their
characteristics
 Custom classes can also implement these interfaces
 For example, create a custom class ListBoxTest that holds
the strings it displays
 The class can implement the collection interfaces to provide
standard methods for:
 Indexing
 Sorting
 Enumeration

154

The Collection Interfaces 2
Interface Purpose
IEnumerable Enumerate a through a collection using the foreach
statement
IEnumerator Iterates over collection & supports the foreach
statement
ICollection Implemented by all collections

IComparer Compares two objects: used for sorting

IList Used by collections that can be indexed

IDictionary For key/value collections such as HashTable and
SortedList
IDictionaryEnumerator Iterates over dictionary & supports the foreach
statement 155

Array Lists
 An array list is like an array
 But, its size is dynamically increased as
required
 It provides many useful properties and
methods

156

Array List Members
Method or Purpose
Property
Capacity() The number of elements the ArrayList can hold
Count() The current number of ArrayList elements
Item() Get or set the ArrayList elements at the specified index
Add() Adds an object at the end of the ArrayList.
Insert() Inserts an element into the ArrayList at the specified index.
RemoveAt() Removes the element at the specified index of the ArrayList
Reverse() Reverses the order of the elements in the ArrayList or a
portion of it
Sort() Sort alphabetically the array list
ToArray() Copy the elements of the ArrayList to a new array
157

Array List Example
ArrayList empArray = new ArrayList();
ArrayList intArray = new ArrayList();
Populate the
for (int i = 0;i<5;i++) ArrayLists
{
empArray.Add(new Employee(i+100));
intArray.Add(i*5);
}

foreach (int i in intArray)
{
Console.Write("{0} ", i.ToString()); Print the
}
ArrayLists‟
foreach(Employee e in empArray) members
{
Console.Write("{0} ", e.ToString());
}
158

Queues
 Queues are a first-in, first-out collection (FIFO)
 Imagine a queue at a bus stop
 Queues are good for managing limited
resources e.g. messages

159

Queues Members
Method or Purpose
Property
Count() Gets the number of elements in the Queue
Clear() Remove all objects
Contains() Determines if an element is in the Queue
CopyTo() Copies elements to a one-dimensional array
Dequeue() Remove and return an object at start of the Queue
Enqueue() Add an object at end of the Queue
Peek() Returns an object at start of the Queue without removing it
ToArray() Copy the elements of the Queue to a new array

160

A Queue Example
Populate the
Queue intQueue = new Queue(); Queue
for (int i = 0;i<5;i++)
{
intQueue.Enqueue(i*5);
}
Console.Write("intQueue values:t" ); Remove
DisplayValues( intQueue ); elements

Console.WriteLine("n(Dequeue)t{0}", intQueue.Dequeue() );
DisplayValues( intQueue );

Console.WriteLine("n(Dequeue)t{0}", intQueue.Dequeue() );
DisplayValues( intQueue );
View but
Console.WriteLine("n(Peek) t{0}", intQueue.Peek() ); do not
DisplayValues( intQueue ); remove
elements
161

Displaying Queue Values
The parameter type
is IEnumerable

public static void DisplayValues( IEnumerable myCollection )
{
IEnumerator myEnumerator = myCollection.GetEnumerator();
while ( myEnumerator.MoveNext() )
Console.Write( "{0} ",myEnumerator.Current );
Console.WriteLine();
}

Iterate thought items
of the collection

How does the IEnumerable
interface work?
162

Stacks
 Queues are a last-in, first-out collection (LIFO)
 Imagine a stack of dishes on a buffet table
 The principal methods for adding and
removing items are Push() and Pop()

163

Stack Members
Method or Purpose
Property
Count() Gets the number of elements in the Stack
Clear() Remove all objects
Contains() Determines if an element is in the Stack
CopyTo() Copies elements to a one-dimensional array
Pop() Remove and return an object at top of the Stack
Push() Add an object at top of the Stack
Peek() Return an object at top of the Stack without removing it
ToArray() Copy the elements of the Stack to a new array

164

A Stack Example
Declare &
populate the
Stack intStack = new Stack(); stack
for (int i = 0;i<8;i++)
{
intStack.Push(i*5); Remove an
} element

Console.WriteLine( "n(Pop)t{0}", intStack.Pop() ); View an
element
Console.WriteLine( "n(Peek) t{0}",intStack.Peek() );

DisplayValues( intStack );

Display all
elements
165

Displaying Stack Values
The parameter is
of type
public static void DisplayValues( IEnumerable
IEnumerable myCollection )
{
foreach (object o in myCollection)
{
Console.WriteLine(o);
}
}

Iterate thought items
of the collection

166

Unit 14 Lab
1. To create an ArrayList of integers. Use looping statements to
populate this with multiples of 10. Experiment with the ArrayLists
methods, including the Sort(), Reverse() and Clear() methods.

2. To create a Queue of integers. Use looping statements to
populate this. Experiment with the Queues methods, including the
Dequeue(),Enqueue () and Peek() methods.

3. To create a Stack of integers. Use looping statements to populate
this. Experiment with the Stacks methods, including the Pop(),Push
() and Peek() methods.

167

15. Strings
 Creating Strings
 Manipulation Stings
 Concatenating Strings
 Copying Strings
 Splitting Strings

 The StringBuilder Class
 Regular Expressions

168

What Exactly are Strings?
 Strings hold a variable number of characters
 C# provides the built in string type
 This aliases the System.String .Net class
 Strings are objects with methods for:
 Concatenation
 Comparison
 Extracting sub-stings

169

Creating Strings
Declare a
string s1 = "abcd"; string

Declare a string with an
string s2 = "ABCDn"; escape character for a
new line

string s3 = "ABCDt EFGH"; Use an escape
character for a tab

string s4 = myInteger.ToString();

Use the ToString() method 170

Comparing Strings
string s1 = "abcd"; Hold the results of comparisons
string s2 = "ABCD";
int result;
Compare two strings, case sensitive
result = string.Compare(s1, s2);
Console.WriteLine("compare s1: {0}, s2: {1}, result: {2}n",
s1, s2, result);
Compare, case insensitive
result = string.Compare(s1,s2, true);
Console.WriteLine("Compare insensitive. result: {0}n",
result);

If result is negative, the first value is smaller
If result is positive, the first value is bigger
If result is zero, the values are equal
171

Concatenating Strings

Concatenation method

string s3 = string.Concat(s1,s2);

string s4 = s1 + s2;

Use the overloaded +
operator

172

Copying Strings
Copy method

string s5 = string.Copy(s2);

string s6 = s5;

Use the overloaded =
operator

173

Test for Equality
Use the member
if s6.Equals(s5)…; method

if string.Equals(s6,s5)…; Use the static
method

if s6 == s5 …;
Use the
overloaded ==
operator

174

Other Useful Methods
Method Return value or action
s3.Length The number of characters in s3

s3[4] The 5th character of s3

s3.EndsWith("Training") True if s3 ends with “Training”

s3.IndexOf("Training") The index of the substring

s3.Insert(101,“Excellent “) Insert the substring at 101st character

175

Splitting Strings 1
string s1 = "One.Two;Three Four";
A string to split
const char Space = ' ';
const char Comma = ',';
const char Stop = '.'; The string
const char SemiColon = ';';
delimiters
char[] delimiters = new char[]
{
Space,
Comma,
Stop, Put the
SemiColon delimiters
};
string output = "";
in an array
int ctr = 1;

176

Splitting Strings 2
Split the string

String[] resultArray = s1.Split(delimiters);
foreach (String subString in resultArray)
{
output += ctr++;
output += ": ";
output += subString;
output += "n";
} Iterate over the
Console.WriteLine(output); resulting array of strings

177

The StringBuilder Class
 The class System.Text.StringBuilder can be
used for creating and modifying string
 StringBuilder is mutable, when an instance is
modified, the actual string is modified, not a
copy
 StringBuilder is more efficient than String
because only a single string object is created

178

The StringBuilder Class 2
Use the
StringBuilder
class to build the
StringBuilder output = new StringBuilder(); output
int ctr = 1;
Split the string
foreach (string subString in s1.Split(delimiters))
{
output.AppendFormat("{0}: {1}n",ctr++,subString);
}
Console.WriteLine(output);
AppendFormat appends a
formatted string

179

StringBuilder Methods
Method Explanation
Append() Append string at end of current string

AppendFormat() Append formatted string at end of current string
AppendFormat appends a formatted string
Insert() Insert string at specified position

Length () Retrieve or assign the length of the string

Remove() Remove specified characters

Replace() Replace all specified characters with new characters

180

Regular Expressions
 A powerful language to describe and
manipulate text
 Uses pattern matching to compare string with
wildcards
 Applying a regular expression to a string can
return
A substring
 A modification of the original

181

Regular Expressions 2 Define the
Regular
Expression
string s1 = "One,Two,Three Liberty Associates, Inc.";
Regex theRegex = new Regex(" |, |,");
StringBuilder sBuilder = new StringBuilder(); Spit the string
int id = 1; using the Regular
Expression
foreach (string subString in theRegex.Split(s1))
{
sBuilder.AppendFormat({0}: {1}n", id++, subString);
}
Console.WriteLine("{0}", sBuilder);

182

Unit 15 Lab
To input a string representing a URL. Experimenting with extracting
substrings and splitting the URL using the dot (.) and forward slash
(/) separators.

183


 Exception Handling
 The throw Statement
 The try and catch Statements
 How the Call Stack Works
 The finally Statement
 Dedicated catch Statements

184

Exception Handling
 C# handles errors and abnormal conditions
with exceptions
 Exceptions can be thrown by
A throw statement
 A .Net Framework class
 The operating system (e.g. a security violation)
 Exceptions are caught by code in a catch
block (i.e. an exception handler)

185

The Exception Class
 All exceptions are of type System.Exception or
derived from this
 Exceptions types include
 ArgumentNullException
 InvalidCastException
 OverflowException
 Exception objects provide information on what
went wrong (message, help file, source …)

186

Try and Catch Statements
public void Func1()
{
Test for
Console.WriteLine("Enter Func1...");
try errors in try
{ block
Console.WriteLine("Entering try block...");
Func2(); Run
Console.WriteLine("Exiting try block..."); statement in
} catch block if
catch an error
{ occurs
Console.WriteLine("Exception caught and handled!");
}
Console.WriteLine("Exit Func1...");
}

187

Searching for an Exception Handler
Main
Unwind the call
Statement1 stack looking
Method A
Statement2 Call for a handler
Statement1
MethodA()
Statement2
Statement3
MethodB() Call
Statement4
Statement3
End method Method B
Statement4 Statement1
Search for
handler End method Statement2 Exception
thrown !!
Statement3
Search for
If no exception handler, then handler Statement4
the CLR handles the exception End method
188

The throw Statement
public void Run() The exception
{ is unhandled
Console.WriteLine("Enter Run..."); so the program
Func1(); terminates
Console.WriteLine("Exit Run...");
}
public void Func1()
{
Func2();
}
public void Func2()
{ Throw an
Console.WriteLine("Enter Func2..."); exception
throw new System.Exception();
}
189

How the Call Stack Works
public void Run()
{
Func1();
}
public void Func1()
catch in
{ Func1
try
{
Func2();
}
catch
{
Console.WriteLine("Exception caught and handled!");
}
}
public void Func2() throw in
{ Func2
throw new System.Exception(); Will this
Console.WriteLine("Exit Func2..."); statement run?
}
190

Creating Dedicated catch Statements

 So far we have used a generic catch statement
 The catch statement can trap specific
exceptions
 Multiple catch statements can trap different
exceptions

191

Creating Dedicated catch Statements 2
try
{
double a = 5;
double b = 0;
DoDivide(a,b) The most derived exception type is first
}
catch (System.DivideByZeroException)
{
Console.WriteLine("DivideByZeroException caught!");
}
catch (System.ArithmeticException)
{
Console.WriteLine("ArithmeticException caught!");
}
catch
{
Console.WriteLine("Unknown exception caught");
}
Why are the catch
statements in this
The generic exception type is last order ? 192

The finally Statement
try
{
double a = 5;
double b = 0;
DoDivide(a,b)
}
catch (System.DivideByZeroException)
{
Console.WriteLine("DivideByZeroException caught!");
}
catch
{
Console.WriteLine("Unknown exception caught");
}
finally This statement
{ must execute
Console.WriteLine(“close files here");
}
What is another way of making
this statement always run ? 193

Exception Class Methods and Properties

Member Explanation
Source The method that raised the exception

Message Information about the exception

Helplink Link to a help file

StackTrace Method calls that lead to the exception

InnerException The exception that caused the current exception

194

Using the Exception Class
DivideByZeroException e = new DivideByZeroException();
e.HelpLink ="http://www.la.com";
throw e;
Set exception
property

catch (System.DivideByZeroException e)
{
Console.WriteLine("nDivideByZeroException! Msg: {0}",e.Message);
Console.WriteLine("nHelpLink: {0}", e.HelpLink);
Console.WriteLine("nHere's a stack trace: {0}n",.StackTrace);
}

Display exception
properties
195

Unit 16 Lab
To divide two integers and add exception handling with dedicated
catch statements to create division by zero and other exceptions.
Include a finally statement.

196

So what are
 Robin Cook has died delegates?
 Tony Blair is not available
 Define in advance what authority to delegate
 Funeral Attendances
 and what “parameters” are passed
 Condolences and flowers
 Delegate the task at “runtime”
 John Prescott attends the funeral

197

Delegates in C#
 A delegate
 encapsulates a method
 has a specific return type & parameter list
 is instantiated with by passing a method as parameter
 can call the delegated method at runtime

198

Using Delegates
 Define the delegate
Public delegate int WhichIsFirst(object obj1, object obj2);

 Instantiate the delegate with a method
WhichIsFirst theStudentDelegate = new
WhichIsFirst(WhichStudentComesFirst);

 Call the delegated method
i= theStudentDelegate(objJohn, objFred);

199

Multicasting Delegates
 Create a single delegate
 that calls multiple methods
 Combine delegates with the + or += operators
myMulticastDelegate = Writer + Logger;

200

Multicasting Delegates
// Define delegate
public delegate void StringDelegate(string s);

// Define two methods
public static void WriteString(string s) { …}
public static void LogString(string s) {…}

// Define and instantiate two StringDelegate objects.
StringDelegate Writer, Logger
Writer = new StringDelegate(WriteString);
Logger = new StringDelegate(LogString);

//Multicast the delegate
myMulticastDelegate = Writer + Logger;

//Call the two delegated methods
myMulticastDelegate(“log this string")
201

Events in C#
 An object publishes a set of events
 Other classes can subscribe to these events
 For example, GUI control classes publish:
 Mouse events
 Keyboard events
 The publishing class also defines delegates
 The subscribing class implements these delegates

202

Events and Delegates

Event this.button1.Click

Instantiate this.button1.Click += new System.EventHandler(this.button1_Click);
Delegate

Event Handler private void button1_Click(object sender, System.EventArgs e)

203

Coupling Delegates to Event Handlers

Delegates Event Handlers

linkLabel1.MouseEnter += new EventHandler(Bigger);

204

Unit 17 Lab
To create a class Pair and include a delegate WhichisFirst, a
constructor, and methods called Sort() and ReverseSort(). These
methods take as a parameters an instance of the WhichisFirst
delegate. To test the class create a Dog class. This implements
methods that can be encapsulated by the delegate.

205

18. Generics
 New feature of C# Version 2.0 and the CLR
 Generics allow a type parameter for classes and
methods
 Specification of the type is deferred to instantiation
at runtime
 Generic classes may be constrained to hold only
certain types of data
 Generics are most commonly used with collections

206

Using Generics
// Declare the generic class public class
class MyList<T>
{
....//
}

// Declare a list of type
MyList<int> list1 = new MyList<int>();

// Declare a list of type string
MyList<string> list2 = new MyList<string>();

// Declare a list of type MyClass
MyList<MyClass> list3 = new MyList<MyClass>();

207

The Reason for Generics
 An ArrayList can hold objects of any type
 All objects are cast to the System.Object root class
 But, the overheads of casting will degrade performance
 Also, there is no way at compile time to prevent invalid
assignments, like:
arrayList1(9) =“A string”;
int myInt = arrayList(9);

208

The Benefits of Generics
Import the Generic
.Net class

Declare a list
using System.Collections.Generic; using the type
parameter
List<int> list1 = new List<int>();
Add element
list1.Add(3);
without casting
or boxing
list1.Add("It is raining in the South West");

Generate compile-
time error!

209

Parameter Constraints
 When defining generic classes restriction can
be placed on the type parameters
 Theses restrictions are called constraints
 They are specified using the where keyword in
the class definition

210

Parameter Constraints
Constraint Explanation
class MyList<T> where The type argument must be a value type
T: struct
class MyList<T> where The type argument must be a reference
T: class type
class MyList<T> where The type argument must have a public
T: new() parameterless constructor
class MyList<T> where The type argument must be or derive from
T: <base class name> the specified base class
class MyList<T> where The type argument must be or implement
T: <interface name> the specified interface

211

Generic Class Inheritance
 A generic class, like any other, can be created by
inheriting from a base class
 The base class can be:
A concrete type
 class Node<T> : BaseNode
A closed constructed type
 class Node<T> : BaseNode<int>
 An open constructed type
 class Node<T> : BaseNode<T>

212

Inheriting from Generic Classes
 Non-generic (concrete) classes can inherit from
closed constructed (generic) base classes
 class Node : BaseNode<int> //No error

 But, not from open constructed (generic) classes
 class Node : BaseNode<T> //Generates an error

 Because, there is no way at run time to supply the
type argument required to instantiate the base class

213

Creating Generic Methods
void Swap<T>( ref T lhs, ref T rhs) A generic
{ method with a
type parameter
T temp;
temp = lhs;
lhs = rhs;
rhs = temp;
} Calling the method
using the type
parameter
int a = 1;
int b = 2;
Swap<int>(ref a, ref b);
Or, calling the method
inferring the type
Swap(ref a, ref b); parameter
214

Unit 18 Lab
Experiment with creating generic classes and methods

215

Unit 19:

New Language Features in C#

New Language Features in C# 3.0
•Implicit Typing

•Anonymous Types

•Object and Collection Initialisers

•Extension Methods

•Partial Methods

•Lambda Expressions

Implicit Typing
• The compiler determines the data type of variable

• The data type is not a variant

• The var keyword is used
• The initialiser cannot be null

var a = 5;
Console.WriteLine("a");
Console.WriteLine("Variable type "+ a.GetType());

Anonymous Types
• The compiler creates a nameless class

• There is an inferred class definition

• The properties are set in the braces

var captain = new { FirstName = "Jamie", LastName = "Cooke" };
Console.WriteLine(captain.FirstName + " " + captain.LastName);

Object and Collection Initialisers
• Initialise an object by setting its properties inline

Person p = new Person{ Name = "Jamie", Age = 50 };

• Initialise a collection using multiple object initialisers

Person[] people = {
new Person { Name="Allen Frances", Age=11},
new Person { Name="Burke Madison", Age=50},
new Person { Name="Connor Morgan", Age=59},
};

Extension Methods
• Extend a class by adding a method

• But put the method in another class

• This is usefully if you do not have the source code of
the first class
• The methods first parameter's type is the original
class
• Extensions methods are used extensively with LINQ
queries
• LINQ provides extension methods for the
IEnumerable & IQueryable classes that are used in
queries

Extension Methods - Part II
//The Money class has a property & a method
public class Money
{ … }

//Add an extension method to the Money class
public static class MoneyExtension
{
public static void AddToAmount(this Money
money, decimal amountToAdd)
{
money.Amount += amountToAdd;
}
} …

//Test the extension method
Money m = new Money();
m.AddToAmount(10);

Partial Methods
•Partial classes allow the class definition to be
contained in several files
•Partial methods allow a method to be
implemented and called in a partial class
•The method implementation can be in one
file and the call in another file

Partial Methods - Part II
//First part of partial class
partial class PartialMethods
{
static void Main()
{
Do();
}
static partial void Do();
}
//Second part of partial class, could be in 2nd file
partial class PartialMethods
{
//Partial method implementation
static partial void Do()
{
Console.WriteLine("Do some work");
}
}

Lambda Expressions
• Anonymous methods provide a concise syntax for
creating delegates
• The method is implemented in a block of code

DelegateTest anonDel = delegate(string param)
{
param += " and this was added";
return param;
};

Lambda Expressions – Part II
• Lambda expression simplify the syntax for creating
anonymous methods
• Lambda expressions are used extensively with LINQ
queries

//Instantiate the delegate using the lambda syntax
DelegateTest anonDel2 = param =>
{
param += " and this was added";
return param;
};

Console.WriteLine(anonDel2("Start of string"));

Summary
Unit Topic
3. Branching
4. Operators
7. Inside Methods
8. Debugging
9. Inheritance and Polymorphism
227

Summary
Unit Topic
11. Structs
12. Interfaces
13. Arrays
15. Strings
18. Generics
19. New Language Features
228

Contact

 David Ringsell MCPD
 More courses and tutorials: www.talk-it.biz
 david@talk-it.biz

229

How To Code in C#

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