1. Object Oriented Programming
Introduction to C#
Dr. Mike Spann

2. Contents Introducing C# Writing applications in C# Visual Studio .NET
Basic C# language concepts

3. Introducing C#
C# (‘C-sharp’) is a language that targets one and only one platform, namely .NET
That doesn’t mean it’s restricted to Windows
There are now .NET implementations on other operating systems including Linux
As long as we get to grips with object oriented programming, C# is a simple language to master

4. Introducing C#
C# derives it’s power from .NET and the framework class library
The most similar language to C# is Java
There are a number of striking similarities
BUT there is one fundamental difference
Java runs on a virtual machine and is interpreted
C# programs runs in native machine code
This is because of the power of .NET and leads to much more efficient programs

5. Writing applications in C#
An application in C# can be one of three types
Console application (.exe)
Windows application (.exe)
Library of Types (.dll)
The .dll is not executable
These 3 types exclude the more advanced web-based applications

6. Writing applications in C#
Before we look at the more detailed structure and syntax of C# programs, we will show a simple example of each type
In each case we will use the command line compiler (csc) to create the binary (assembly)
Later in this lecture we will look at using Visual Studio to create our applications

7. Writing applications in C#
Example 1 – A console application
This example inputs a number from the console and displays the square root back to the console
Uses a simple iterative algorithm rather than calling a Math library function

8. Writing applications in C#
using System;
class Square_Root {
static void Main(string[] args)
double a,root; do
Console.Write("Enter a number: ");
a=Convert.ToDouble(Console.ReadLine());
if (a<0)
Console.WriteLine(“Enter a positive number!");
} while (a<0);
root=a/2;
double root_old;
root_old=root;
root=(root_old+a/root_old)/2;
} while (Math.Abs(root_old-root)>1.0E-6);
Console.WriteLine("The square root of " + a + " is " + root); }

9. Writing applications in C#

10. Writing applications in C#
We can see that everything in a C# application is in a class
In this case the class defines a program entry point Main
This makes the application binary an executable
Note the use of the System namespace
Classes referred to such as Console and Math actually System.Console and System.Math

11. Writing applications in C#
Example 2 – A windows application
A simple GUI displaying a menu
This example displays a window with couple of menu buttons
Clicking on a menu button displays a pop-up dialog box
The code listing demonstrates the simplicity of GUI programming in C#

12. Writing applications in C#
using System;
using System.Drawing;
using System.Windows.Forms;
class App{
public static void Main(){
Application.Run(new MenuForm()); }
class MenuForm:Form{
public MenuForm(){
this.ContextMenu = new ContextMenu(SetupMenu());
this.Menu = new MainMenu(SetupMenu());
MenuItem[] SetupMenu(){
MenuItem file = new MenuItem("&File");
file.MenuItems.Add("Exit", new EventHandler(OnExit));
MenuItem messages = new MenuItem("&Message Boxes");
EventHandler handler = new EventHandler(OnMessageBox);
messages.MenuItems.Add("Message Box 1", handler);
messages.MenuItems.Add("Message Box 2", handler);
return new MenuItem[]{file, messages};
void OnExit(Object sender, EventArgs args){
this.Close();
void OnMessageBox(Object sender, EventArgs args){
MenuItem item = sender as MenuItem;
MessageBox.Show(this, "You selected menu item - "+item.Text);

13. Writing applications in C#

14. Writing applications in C#

15. Writing applications in C#
This program is considerably more complex than the previous example
It uses the System.Drawing and System.Windows.Forms namespaces
The (System.Windows.Forms).Form class is a standard outer graphics container for most windows/GUI applications
It also uses event handling to respond to user interaction (menu button clicks)

16. Writing applications in C#
Example 3 – A library
We can take some of the code from example 1 for computing the square root and make it a library
It will not have a Main method
We indicate that we are compiling to a .dll using the /Target:library option

17. Writing applications in C#
using System;
public class Square_Root_Class {
public static double calcRoot(double number)
double root;
root=number/2;
double root_old; do
root_old=root;
root=(root_old+number/root_old)/2;
} while (Math.Abs(root_old-root)>1.0E-6);
return root; }

18. Writing applications in C#

19. Writing applications in C#
We can now write a simple program containing a Main method which uses this library class
The only thing we need to do is to reference the library .dll using the /r switch when we compile the application

20. Writing applications in C#
using System;
class Square_Root {
static void Main(string[] args)
double a,root; do
Console.Write("Enter a number: ");
a=Convert.ToDouble(Console.ReadLine());
if (a<0)
Console.WriteLine("Please enter a positive number!");
} while (a<0);
root=Square_Root_Class.calcRoot(a);
Console.WriteLine("The square root of " + a + " is " + root); }

21. Writing applications in C#

22. Visual Studio .NET
VS.NET is an Integrated Development Environment or IDE
It includes a source code editors (usually pretty fancy ones containing language help features)
Software project management tools
Online-help and
Debugging
GUI design tools
And lots more......

23. Visual Studio .NET
Creating a new project gives the user the option of the language and project type
Visual Basic, C++, C#, J#
Console, Windows, Class Library, Active Web Page or Web Service

24. Visual Studio .NET

25. Visual Studio .NET We can group our projects under a common solution
Each application has just one solution but may comprise many projects
A single solution can comprise projects written in different languages
Each project contains a number of files including source files, executables and xml files containing information about the project and resources

26. Visual Studio .NET
We can add each of our previous 3 example applications (projects) to a single solution Learning C Sharp
Its a simple matter to flip between them and view the code from each project by selecting the appropriate tab
Each project must be built (compiled) before executing and any of the projects in a solution can be selected to be executed

27. Visual Studio .NET

28. Visual Studio .NET
It is a simple matter to reference a .dll from a project
We can check all the references that a project makes by expanding the References menu item in the solution explorer
Notice for the windows project, lots of FCL classes are referenced

29. Visual Studio .NET

30. Visual Studio .NET
An important feature of VS is its ability to enable visual programming
Essentially we can create fairly sophisticated GUI’s without writing a line of code
We simply add GUI components to an outer window (a Form) and set up the properties of the components to get the required look and feel
VS allows us to easily switch between code and design views
We will look more into visual programming in our lab sessions

31. Visual Studio .NET

32. Basic C# language concepts
C# has a rich C-based syntax much like C++ or Java
The concepts of variables, program statements, control flow, operators, exceptions etc are the same in C# as in C++ and Java
Like Java, everything in C# is inside a class{}
We will only look at those C# language issues which differ from those we are already familiar with

33. Basic C# language concepts
Primitive types
These are types representing the basic types we are familiar with – integers, floats, characters etc
In C# they are part of the FCL so they are treated as Objects (unlike in Java!) but are used in the same way as normal primitive types
So, for example, we can apply the normal arithmetic operators to them

34. Basic C# language concepts
C# Primitive
C# Alias
Description
Boolean
bool
Indicates a true or false value. The if, while, and do- while constructs require expressions of type Boolean.
Byte
byte
Numeric type indicating an unsigned 8-bit value.
Char
char
Character type that holds a 16-bit Unicode character.
Decimal
decimal
High-precession numerical type for financial or scientific applications.
Double
double
Double precision floating point numerical value.
Single
float
Single precision floating point numerical value.
Int32
int
Numerical type indicating a 32-bit signed value.
Int64
long
Numerical type indicating a 64-bit signed value.
SByte
sbyte
Numerical type indicating an 8-bit signed value.
Int16
short
Numerical type indicating a 16-bit signed value.
UInt32
uint
Numerical type indicating a 32-bit unsigned value.
UInt64
ulong
Numerical type indicating a 64-bit unsigned value.
UInt16
ushort
Numerical type indicating a 16-bit unsigned value.
String
string
Immutable string of character values
Object
object
The base type of all type in any managed code.

35. Basic C# language concepts
Reference Types and Value Types
When we declare a variable in a C# program it is either a reference or a value type
All non-primitive types are reference types
Essentially the variable name is a reference to the memory occupied by the variable
But primitive types can be either
Even though all primitive types are treated as objects (unlike in Java)!!

36. Basic C# language concepts
For example String and Int32 are both primitive types
BUT
String is a reference type
Int32 is a value type
String variable s is a reference (memory address) of some memory which stores the string (which defaults to null)
Int32 variable x is the actual value of the integer (which defaults to zero)
Int32 x=10;
String s=“Hello”;

37. Basic C# language concepts
Arrays
Array declaration and initialization is similar to other languages
// A one dimensional array of 10 Bytes
Byte[] bytes = new Byte[10];
// A two dimensional array of 4 Int32s
Int32[,] ints = new Int32[5,5];
// A one dimensional array of references to Strings
String[] strings = new String[10];

38. Basic C# language concepts
The array itself is an object
The array in is automatically derived from the Array class in the FCL
This enables a number of useful methods of the Array class to be used
Finding the length of an array
Finding the number of dimensions of an array
Arrays themselves are reference types although their elements can be value types, or reference types

39. Basic C# language concepts
Control flow statements in C# are the same as for C++ and Java
if {} else{}
for {}
do{} while()
etc
However, there is one additional new one in C#!
foreach

40. Basic C# language concepts
foreach simplifies the code for iterating through an array
There is no loop counter
If the loop counter variable is required in the loop, then a for construct must be used
The type must match the type of elements in the array
The array cannot be updated inside the loop
foreach (type identifier in arrayName)

41. Basic C# language concepts
using System;
public class ForEachTest {
static void Main(string[] args)
int[] array ={ 0, 2, 4, 6, 8, 10, 12, 14};
int total = 0;
foreach (int n in array)
total += n;
Console.WriteLine("Array total= " + total); }

42. Basic C# language concepts
Expressions and operators
C# is a strongly typed language
Variables are declared before use
Implicit type conversions that don’t lose precision will be carried out
Unlike C++ (but like Java) C# has a boolean type
Thus the following code generates a compilation error
Int32 x = 10; while(x--) DoSomething();

43. Basic C# language concepts
C# has the standard set of operators we are familiar with
Also it has operators such as is and typeof for testing variable type information
C# provides operator overload functions (as does C++ but not Java) to enable standard operators to be applied to non-primitive types
This is something we shall look at in a future lecture

44. Basic C# language concepts
Operator category
Operators
Arithmetic
+ - * / %
Logical (boolean and bitwise)
& | ^ ! ~ && || true false
String concatenation +
Increment, decrement
++  --
Shift
<< >>
Relational
== != < > <= >=
Assignment
= += -= *= /= %=
&= |= ^= <<= >>=
Member access .
Indexing []
Cast ()
Conditional (Ternary) ?:
Delegate concatenation and removal
+ -
Object creation
New
Type information
is sizeof typeof   
Overflow exception control
checked unchecked
Indirection and Address
* -> [] &

45. Basic C# language concepts
Error handling
This is always done in C# using structured exception handling
Use of the try{} catch{} mechanism as in Java and C++
Functions should not return error conditions but should throw exceptions
This is done universally by methods in FCL classes

46. Basic C# language concepts
public static void ExceptionExample() {
// try-catch
try
Int32 index = 10;
while(index-- != 0)
Console.WriteLine(100/index); }
catch(DivideByZeroException)
Console.WriteLine("A divide by zero exception!");
Console.WriteLine("Exception caught; code keeps running");
// try-finally
return;
finally
Console.WriteLine("Code in finally blocks always runs");

47. Summary We have looked at different types of simple C# applications
Console applications
Windows applications
Libraries (reusable types)
We have looked at the basics of using Visual Studio.NET
We have looked at some C# language issues from the point of view of differences from C++ and Java