1. A First Program Using C#
Chapter One
A First Program Using C#

2. Objectives Learn about programming tasks
Learn object-oriented programming concepts
Learn about the C# programming language
Learn how to write a C# program that produces output
Learn how to select identifiers to use within your programs

3. Objective
Learn how to compile and execute a C# program from the command line
Learn how to add comments to a C# program
Learn how to compile and execute a program using Visual Studio IDE
Learn how to eliminate the reference to Out by using the System namespace

4. Programming
A computer program is a set of instructions that you write to tell a computer what to do
Programmers do not use machine language when creating computer programs. Instead, programmers tend to use high-level programming languages
Each high-level language has its own syntax and limited set of vocabulary that is translated into machine code by a compiler
In addition to understanding syntax, a programmer must also understand programming logic

5. Object-Oriented Programming
Variables are named computer memory locations used to hold values that may vary
Operations are usually called or invoked to manipulate variables
A procedural program defines the variable memory locations, then calls a series of procedures to input, manipulate, and output the value stored in those locations
A single procedural program often contains hundreds of variables and thousands of procedure calls

6. Object-Oriented Programming
Object-oriented programming is an extension of procedural programming, which in addition to variables and procedures contains: objects, classes, encapsulation, interfaces, polymorphism, and inheritance
Objects are object-oriented components
Attributes of an object represent its characteristics
A class is a category of objects or a type of object
An instance refers to an object based on a class

7. Object-Oriented Programming
For example:
An Automobile is a class whose objects have the following attributes: year, make, model, color, and current running status
Your 1997 red Chevrolet is an instance of the class that is made up of all Automobiles
Methods of classes are used to change attributes and discover values of attributes
The Automobile class may have the following methods: getGas(), accelerate(), applyBreaks()

8. Object-Oriented Programming
Methods and variables in object-oriented programming are encapsulated, that is, users are only required to understand the interface and not the internal workings of the class
Polymorphism and Inheritance are two distinguishing features in the object-oriented programming approach
Polymorphism describes the ability to create methods that act appropriately depending on the context
Inheritance provides the ability to extend a class so as to create a more specific class

9. The C# Programming Language
C# was developed as an object-oriented and component-oriented language
It exists as part of the Visual Studio .NET package
C# (like Java) is modeled after the C++ programming language
Pointers are not used in C#
C# does NOT require the use of object destructors, forward declarations, or #include files
It has the ability to pass by reference
Multiple inheritance is not allowed in C#

10. Writing a C# Program that Produces Output
“This is my first C# program” is a literal string of characters
The string appears in parenthesis because it is a parameter or an argument
The WriteLine() method prints a line of output on the screen

11. Writing a C# Program that Produces Output
Out is an object that represents the screen
The Out object was created and endowed with the method WriteLine()
Not all objects have the WriteLine() method

12. Writing a C# Program that Produces Output
Console is a class
Console defines the attributes of a collection of similar “Console” objects

13. Writing a C# Program that Produces Output
System is a namespace, which is a scheme that provides a way to group similar classes
Namespaces are used to organize classes

14. Writing a C# Program that Produces Output
The difference between the above code and the previous code is the amount of whitespace
Both versions of code share the same method header (including access modifiers and other keywords)

15. Selecting Identifiers
Every method used in C# must be part of a class
A C# class name or identifier must meet the basic following requirements:
An identifier must begin with an underscore or a letter
An identifier can contain only letters or digits, not special characters such as #,$, or &
An identifier cannot be a C# reserved keyword

16. Selecting Identifiers
The reserved public keyword is an access modifier that defines the circumstance under which a class can be accessed

17. Writing a C# Program that Produces Output
Code written for a C# program using a text editor

18. Compiling and Executing a Program from the Command Line
After creating source code, you must do the following before you can view the program output:
Compile the source code into intermediate language (IL)
Use the C# just in time (JIT) compiler to translate the intermediate code into executable statements

19. Compiling and Executing a Program from the Command Line
Output of Hello Program

20. Adding Comments to a Program
In large programs it becomes difficult to remember why certain steps were included and the role of certain variables and methods
Program comments are nonexecuting statements that you add to document a program
You can also comment out various statements in a program to debug and observe the effects of the program with the statement or statements commented out

21. Adding Comments to a Program
There are three types of comments in C#:
Line comments
Block comments
XML-documentation format

22. Compiling and Executing a Program Using the Visual Studio IDE
C# programs can also be written using the Visual Studio IDE (instead of a text editor). This approach offers many advantages including:
Some of the code you need is already created for you
The code is displayed in color, so you can more easily identify parts of your program
If error messages appear when you compile your program, you can double-click on an error message and the cursor will move to the line of code that contains the error
Other debugging tools are available

23. Overview of the Visual Studio 2005 IDE
Microsoft Visual C# Express Edition
Only support Visual C# programming language
Start page
A list of links to resources in the IDE and on the internet
Visual C# Express Headlines and MSDN
This section provides links to information about programming in C#
Note: MSDN stands for Microsoft Developer Network

24. Start Page in Visual C# 2005 Express Edition.
Hidden
window
Start Page links
Empty Solution
Explorer (no
projects open)
New Project
button
Start Page
tab
Start Page in Visual C# 2005 Express Edition.

25. Displaying a Web page in Visual Studio.
Requested Web page
(URL in location bar
drop-down menu)
Selected tab requested Web page
Displaying a Web page in Visual Studio.

26. Creating a Console Application with the New Project dialog.
Project name
Creating a Console Application with the New Project dialog.

27. IDE with an open console application.
Editor window
IDE with an open console application.

28. Renaming the program file in the Properties window.
Solution Explorer
Properties window
File Name Property
Click Program.cs to
display its properties
Type Welcome1.cs here
to rename the file
Renaming the program file in the Properties window.

29. Compiling and Executing a Program Using the Visual Studio IDE
Output of the Hello program as run from the Visual Studio IDE

30. Compiling and Executing a Program Using the Visual Studio IDE
List of Hello Program Files

31. Eliminating the Reference to Out by Using the System Namespace
A program may contain an unlimited number of statements, as long as they are each terminated by a semicolon

32. Eliminating the Reference to Out by Using the System Namespace
The Output of ThreeLines program

33. Eliminating the Reference to Out by Using the System Namespace
When you need to repeatedly use a class from the same namespace, you can shorten statements by using the “using” keyword
Output is identical as the previous version of ThreeLines

34. Eliminating the Reference to Out by Using the System Namespace
An alias is an alternative name for a class
An alias can be used to shorten a long class name (as in the above example)

35. Chapter Summary
A computer program is a set of instructions that you write to tell a computer what to do
Procedural Programming involves creating computer memory locations, called variables, and a set of operations, called procedures. In object-oriented programming, you envision program components as objects that are similar to concrete objects in the real world
The C# language was developed as an object-oriented and component-oriented language

36. Chapter Summary
To write a C# program that produces a line of console output, you must pass a literal string as a parameter to the System.Console.Out.WriteLine() method
You can define a C# class or variable by using any name or identifier that begins with an underscore or a letter, that contains only letters or digits, and that is not a C# reserved keyword
To create a C# program, you can use the Microsoft Visual Studio environment or any text editor

37. Chapter Summary
After you write and save a program, you must compile the source code
Program comments are nonexecuting statements that add to document a program or to disable statements
As an alternative to using the command line, you can compile and write your program within the Visual Studio IDE
When you need to repeatedly use a class from the same namespace, you can shorten the statements you type by using a clause that indicates a namespace where the class can be found