The document provides an introduction to variables in C#, including value types like integers and reference types like objects. It discusses defining and assigning values to variables, and differences between static and non-static classes. Examples show creating a basic console application in C# and getting input from the user via arguments or keyboard. Exercises guide practicing variable usage, type conversion, and writing simple programs to calculate averages and swap values.

1. Chapter 2Getting Started with C#

2. What is a variable?Variable: imagine like a box to store one thing (data)Eg: int age; age = 5;

3. What is a variable?Variable: imagine like a box to store one thing (data)Eg: int age; age = 5;int - Size of variable must be big enough to store Integer

4. What is a variable?Variable: imagine like a box to store one thing (data)Eg: int age; age = 5;int - Size of variable must be big enough to store Integerage - Name of variableage

5. What is a variable?Variable: imagine like a box to store one thing (data)Eg: int age; age = 5;5int - Size of variable must be big enough to store Integerage - Name of variableageage = 5 – Put a data 5 into the variable

6. Value Type Vs Reference TypeVariables: two typesValue type (simple type like what you just saw)Only need to store one thing (5, 3.5, true/false, ‘C’ and “string”)Reference type (complex type for objects)Need to store more than one thing (age + height + run() + … )

7. Reference TypeReference type (complex type for objects)Eg: Human john; john = new Human();Compare this to int age;age = 5;

8. Reference TypeReference type (complex type for objects)Eg: Human john; john = new Human();Human - Size of variable must be big enough to store an Address

9. johnReference TypeReference type (complex type for objects)Eg: Human john; john = new Human();Human - Size of variable must be big enough to store an Addressjohn - Name of variable

10. Reference TypeReference type (complex type for objects)Eg: Human john; john = new Human();Human - Size of variable must be big enough to store an AddressD403john - Name of variable…ageheightjohn = new Human() – Get a house with enough space for john (age, height, etc)john

11. Non-Static Vs Static ClassNon-Static: need New() to instantiate / create an object – like what you see just nowStatic: NO need to use New() to use, there is just one copy of the class. This type of class basically to provide special functions for other objects So if you see a class being used without New(): it is a static classEgMathclass age = Math.Round(18.5); // Math rounding

12. First Console ProgramA new project:

13. Understanding Program.csusing System;namespace ConsoleApplication1{ class Program { static void Main(string[] args) { } }}

14. Understanding Program.csusing System;namespace ConsoleApplication1{ class Program { static void Main(string[] args) { } }}What is a namespace?It is simply a logical collection of related classes. Egnamespace System{publicstatic class Console { …. // with properties and methods } class xxxx { …. // with properties and methods }}

15. Understanding Program.csusing System;namespace ConsoleApplication1{ class Program { static void Main(string[] args) { } }}What is a namespace?It is simply a logical collection of related classes. Egnamespace System{publicstatic class Console { …. // with properties and methods } class xxxx { …. // with properties and methods }}Access Modifiers – on class, its properties and methodsTypes: public, private, protectedpublic: Access is not restricted.private: Access is limited to the containing type.protected: Access is limited to the containing class or types derived from the containing class.

16. Group Exercisepublic class Apple{ public OutputVariety() { … } protected ReadColour() { …. } private ResetColour() { …. }}class AnotherClass{ …. }class DerivedClass: Apple { …. }Which class could access the 3 methods?

17. Understanding Program.csusing System;namespace ConsoleApplication1{ class Program {static void Main(string[] args) { } }}

18. Understanding Program.csusing System;namespace ConsoleApplication1{ class Program { static void Main(string[] args) { } }}Inside a namespace, may contain internal namespace.namespace System{ namespace Data { …. // with classes & their properties and methods }}OR combine with a “.”Namespace System.Data{ …. // with classes & their properties and methods}

19. Group Exercisenamespace ITE.MP.GDD{ public class 2W { public intClassSize; }}namespace ITE.MP.EC{ public class 2W { public intClassSize; }}How to access ClassSize for one ITE.MP.GDD.2W object?

20. Add code and run programAdd following code into main()Console.WriteLine("Welcome!"); > View >output> Build > Build Solution> Debug > Start Without Debugging

21. Understanding Program.csDemo: Remove all “using” statements and correct error - instead of Console.WriteLine(), change to System.Console.WriteLine() Demo: Using refactor to rename “Program” to “HelloWorld”Demo: Right click on Console > Go To Definition- take a look at the Console class and its WriteLine method

22. Main(string[] args)string[] args // string array // with name argsGetting inputs from commandlineConsole.WriteLine("Hello " + args[0]);

23. Setting ArgumentsArgument is what user key in after the program fileEg for Unreal Tournament, to use the editor, user type “ut.exe editor” => editor is an argumentIn console program, there are two ways to key in arguments for running the program:1. Using IDE 2. Use command prompt

24. Setting arguments using IDEIn Solution Explorer, right click the project and select Properties:

25. Setting arguments using cmdStart > run > cmdUse cd, dir to move to the projet debug folder: …. myFirstProgram\bin\Debug>> myFirstProgram.exe joe

26. C# Application Programming Interface (API)C# APIor.NET Framework Class Library Referencehttp://msdn.microsoft.com/en-us/library/ms229335.aspx

27. RecapConsole program:SimpleProcedural (from top to bottom)Inputs: Arguments: How?Eg Unreal Tournament Editor: > UT.exe editorMore useful to take inputs from Keyboard: How?

28. Guided Hands onLaunch Visual Studio 2008 – C#Create a new console projectAdd the following line into main(..)Console.WriteLine("Hello " + args[0]);Add argument “James“Build and run

29. Get input from keyboardstatic void Main() { string str; // A string variable to hold inputConsole.Write(“Your input:"); str = Console.ReadLine(); // Wait for inputsConsole.WriteLine("You entered: " + str); }

30. Exercise 2.1Create your first console programRemove the unused namespacesUse refactor to rename your class to YourFullName Refer to the following URL for Naming Convention for Class:http://alturl.com/6uzphttp://alturl.com/o7fiWhat you see on screen (blue by computer, red by user)Your Input: 3Output: 3 3 3 3 3

31. Type conversionNeed to tell computer to convert fromstring to integer/doublestring str; // a string variablestr = Console.Readline(); // get inputintnumberInteger; // an integer variable// convert string type to integer typenumberInteger = int.Parse(str);double numberDouble; // a decimal variable// convert string type to decimal typenumberDouble = double.Parse(str)

32. Exercise 2.2 Write a program that asks the user to type 5 integers and writes the average of the 5 integers. This program can use only 2 variables. Hint 1: Use decimal instead of integereg: doublemyNumber; Hint 2: conversion from string to doubleeg: myNumber = double.Parse(str);=> Next page for screen output

33. Exercise 2.2 What you see on screen (blue by computer, red by user)Input1: 1Input2: 4Input3: 4Input4: 2Input5: 3Average: 2.8

34. Exercise 2.3 Write a program that asks the user to type the width and the length of a rectangle and then outputs to the screen the area and the perimeter of that rectangle. Hint: 1) Assume that the width and length are integers 2) eg: width = int.Parse(str); 3) Operator for multiplication: *eg: area = width * length;=> Next page for screen output

35. Exercise 2.3 What you see on screen (blue by computer, red by user)Width: 5Length: 4Area:20 and Perimeter:18

36. Exercise 2.4 Write a program that asks the user to type 2 integers A and B and exchange the value of A and B.Hint:1) To swop 2 variable, you need another variable to store one of the value 2) Eg for ascending order (small to Big) if (n1 > n2) { n3 = n2; n2 = n1; n1 = n3; } “then” processing

37. Exercise 2.4 What you see on screen (blue by computer, red by user)Input1: 1Input2: 4Input1: 4 Input2: 1

38. Exercise 2.5Prompt user to key in 3 integers.Sort the integers in ascending order.Print the 3 integers as you sort.Eg:Input1: 2Input2: 1Input3: 0210120102012if (n1 > n2) { … }if (n2 > n3) { … }if (n1 > n2) { … }

39. SummaryC# Language Fundamentals covered:int, double, string, Console.WriteLine(), Console.Write(), Console.ReadLine(), int.Parse(), double.Parse(), simple if then statementProblem solving skills covered:repeating steps