Chapter 2Getting Started with C#

What is a variable?

Variable: imagine like a box to store one thing (data)

Eg: int age; age = 5;

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

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 variable

age

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 variable

age = 5 – Put a data 5 into the variable

age

5

Value Type Vs Reference Type

Variables: two types◦Value 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() + … )

Reference Type

Reference type (complex type for objects)Eg: Human john; john = new Human();

Compare this to int age;age = 5;

Reference Type

Reference type (complex type for objects)Eg: Human john; john = new Human();

Human - Size of variable must be big enough to store an Address

john

Reference Type

Reference 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

Reference Type

Reference 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

john = new Human() – Get a house with enough space for john (age, height, etc)

john

D403

age

height

…

Non-Static Vs Static Class

Non-Static: need New() to instantiate / create an object – like what you see just now

Static: 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 class

Eg Math class age = Math.Round(18.5); // Math rounding

First Console Program

A new project:

Understanding Program.cs

using System;

namespace ConsoleApplication1{ class Program { static void Main(string[] args) { } }}

Understanding Program.cs

using 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{ public static class Console { …. // with properties and methods } class xxxx { …. // with properties and methods }}

Understanding Program.cs

using 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{ public static class Console { …. // with properties and methods } class xxxx { …. // with properties and methods }}

Access Modifiers – on class, its properties and methodsTypes: public, private, protected

public: 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.

Group Exercise

public class Apple{ public OutputVariety() { … } protected ReadColour() { …. } private ResetColour() { …. }}class AnotherClass{ …. }class DerivedClass : Apple { …. }

Which class could access the 3 methods?

Understanding Program.cs

using System;

namespace ConsoleApplication1{ class Program { static void Main(string[] args) { } }}

Understanding Program.cs

using 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}

Group Exercise

namespace ITE.MP.GDD{ public class 2W { public int ClassSize; }}namespace ITE.MP.EC{ public class 2W { public int ClassSize; }}

How to access ClassSize for one ITE.MP.GDD.2W object?

Add code and run program

Add following code into main()

Console.WriteLine("Welcome!");

> View >output> Build > Build Solution> Debug > Start Without Debugging

Understanding Program.cs

Demo: 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

Main(string[] args)

string[] args // string array // with name args

Getting inputs from commandline

Console.WriteLine("Hello " + args[0]);

•First argument

args[0]

•Second argument

args[1]•T

hird argument

args[2]

Setting Arguments

Argument is what user key in after the program file

Eg for Unreal Tournament, to use the editor, user type “ut.exe editor” => editor is an argument

In console program, there are two ways to key in arguments for running the program:

1. Using IDE 2. Use command prompt

Setting arguments using IDE

In Solution Explorer, right click the project and select Properties:

Setting arguments using cmd

Start > run > cmdUse cd, dir to move to the projet debug

folder: …. myFirstProgram\bin\Debug>> myFirstProgram.exe joe

C# Application Programming Interface (API)

C# APIor.NET Framework Class Library Reference

http://msdn.microsoft.com/en-us/library/ms229335.aspx

Recap

Console program:◦Simple◦Procedural (from top to bottom)◦Inputs:

Arguments: How? Eg Unreal Tournament Editor: > UT.exe editor

More useful to take inputs from Keyboard: How?

Guided Hands on

Launch 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

Get input from keyboard

static void Main() { string str; // A string variable to hold input Console.Write(“Your input:");

str = Console.ReadLine(); // Wait for inputs

Console.WriteLine("You entered: " + str); }

Exercise 2.1

Create 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/6uzp

http://alturl.com/o7fi

What you see on screen (blue by computer, red by user)

Your Input: 3Output: 3 3 3 3 3

Type conversion

Need to tell computer to convert fromstring to integer/double

string str; // a string variablestr = Console.Readline(); // get inputint numberInteger; // 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)

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 integer eg: double myNumber; Hint 2: conversion from string to double eg: myNumber = double.Parse(str);

=> Next page for screen output

Exercise 2.2

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

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

Exercise 2.3

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

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

Exercise 2.4

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

Exercise 2.5

Prompt user to key in 3 integers.Sort the integers in ascending order.Print the 3 integers as you sort.Eg:Input1: 2Input2: 1Input3: 0210120102012

if (n1 > n2) { … }

if (n2 > n3) { … }

if (n1 > n2) { … }

Summary

C# Language Fundamentals covered:

int, double, string, Console.WriteLine(), Console.Write(), Console.ReadLine(), int.Parse(), double.Parse(), simple if then statement

Problem solving skills covered:

repeating steps swopping of 2

variables simple sorting