- •Microsoft C# Programming for the Absolute Beginner
- •Table of Contents
- •Microsoft C# Programming for the Absolute Beginner
- •Introduction
- •Overview
- •Chapter 1: Basic Input and Output: A Mini Adventure
- •Project: The Mini Adventure
- •Reviewing Basic C# Concepts
- •Namespaces
- •Classes
- •Methods
- •Statements
- •The Console Object
- •.NET Documentation
- •Getting into the Visual Studio .Net Environment
- •Examining the Default Code
- •Creating a Custom Namespace
- •Adding Summary Comments
- •Creating the Class
- •Moving from Code to a Program
- •Compiling Your Program
- •Looking for Bugs
- •Getting Input from the User
- •Creating a String Variable
- •Getting a Value with the Console.ReadLine() Method
- •Incorporating a Variable in Output
- •Combining String Values
- •Combining Strings with Concatenation
- •Adding a Tab Character
- •Using the Newline Sequence
- •Displaying a Backslash
- •Displaying Quotation Marks
- •Launching the Mini Adventure
- •Planning the Story
- •Creating the Variables
- •Getting Values from the User
- •Writing the Output
- •Finishing the Program
- •Summary
- •Chapter 2: Branching and Operators: The Math Game
- •The Math Game
- •Using Numeric Variables
- •The Simple Math Game
- •Numeric Variable Types
- •Integer Variables
- •Long Integers
- •Data Type Problems
- •Math Operators
- •Converting Variables
- •Explicit Casting
- •The Convert Object
- •Creating a Branch in Program Logic
- •The Hi Bill Game
- •Condition Testing
- •The If Statement
- •The Else Clause
- •Multiple Conditions
- •Working with The Switch Statement
- •The Switch Demo Program
- •Examining How Switch Statements Work
- •Creating a Random Number
- •Introducing the Die Roller
- •Exploring the Random Object
- •Creating a Random Double with the .NextDouble() Method
- •Getting the Values of Dice
- •Creating the Math Game
- •Designing the Game
- •Creating the Variables
- •Managing Addition
- •Managing Subtraction
- •Managing Multiplication and Division
- •Checking the Answers
- •Waiting for the Carriage Return
- •Summary
- •Chapter 3: Loops and Strings: The Pig Latin Program
- •Project: The Pig Latin Program
- •Investigating The String Object
- •The String Mangler Program
- •A Closer Look at Strings
- •Using the Object Browser
- •Experimenting with String Methods
- •Performing Common String Manipulations
- •Using a For Loop
- •Examining The Bean Counter Program
- •Creating a Sentry Variable
- •Checking for an Upper Limit
- •Incrementing the Variable
- •Examining the Behavior of the For Loop
- •The Fancy Beans Program
- •Skipping Numbers
- •Counting Backwards
- •Using a Foreach Loop to Break Up a Sentence
- •Using a While Loop
- •The Magic Word Program
- •Writing an Effective While Loop
- •Planning Your Program with the STAIR Process
- •S: State the Problem
- •T: Tool Identification
- •A: Algorithm
- •I: Implementation
- •R: Refinement
- •Applying STAIR to the Pig Latin Program
- •Stating the Problem
- •Identifying the Tools
- •Creating the Algorithm
- •Implementing and Refining
- •Writing the Pig Latin Program
- •Setting Up the Variables
- •Creating the Outside Loop
- •Dividing the Phrase into Words
- •Extracting the First Character
- •Checking for a Vowel
- •Adding Debugging Code
- •Closing Up the code
- •Summary
- •Introducing the Critter Program
- •Creating Methods to Reuse Code
- •The Song Program
- •Building the Main() Method
- •Creating a Simple Method
- •Adding a Parameter
- •Returning a Value
- •Creating a Menu
- •Creating a Main Loop
- •Creating the Sentry Variable
- •Calling a Method
- •Working with the Results
- •Writing the showMenu() Method
- •Getting Input from the User
- •Handling Exceptions
- •Returning a Value
- •Creating a New Object with the CritterName Program
- •Creating the Basic Critter
- •Using Scope Modifiers
- •Using a Public Instance Variable
- •Creating an Instance of the Critter
- •Adding a Method
- •Creating the talk() Method for the CritterTalk Program
- •Changing the Menu to Use the talk() Method
- •Creating a Property in the CritterProp Program
- •Examining the Critter Prop Program
- •Creating the Critter with a Name Property
- •Using Properties as Filters
- •Making the Critter More Lifelike
- •Adding More Private Variables
- •Adding the Age() Method
- •Adding the Eat() Method
- •Adding the Play() Method
- •Modifying the Talk() Method
- •Making Changes in the Main Class
- •Summary
- •Introducing the Snowball Fight
- •Inheritance and Encapsulation
- •Creating a Constructor
- •Adding a Constructor to the Critter Class
- •Creating the CritViewer Class
- •Reviewing the Static Keyword
- •Calling a Constructor from the Main() Method
- •Working with Multiple Files
- •Overloading Constructors
- •Viewing the Improved Critter Class
- •Adding Polymorphism to Your Objects
- •Modifying the Critter Viewer in CritOver to Demonstrate Overloaded Constructors
- •Using Inheritance to Make New Classes
- •Creating a Class to View the Clone
- •Creating the Critter Class
- •Improving an Existing Class
- •Introducing the Glitter Critter
- •Adding Methods to a New Class
- •Changing the Critter Viewer Again
- •Creating the Snowball Fight
- •Building the Fighter
- •Building the Robot Fighter
- •Creating the Main Menu Class
- •Summary
- •Overview
- •Introducing the Visual Critter
- •Thinking Like a GUI Programmer
- •Creating a Graphical User Interface (GUI)
- •Examining the Code of a Windows Program
- •Adding New Namespaces
- •Creating the Form Object
- •Creating a Destructor
- •Creating the Components
- •Setting Component Properties
- •Setting Up the Form
- •Writing the Main() Method
- •Creating an Interactive Program
- •Responding to a Simple Event
- •Creating and Adding the Components
- •Adding an Event to the Program
- •Creating an Event Handler
- •Allowing for Multiple Selections
- •Choosing a Font with Selection Controls
- •Creating the User Interface
- •Examining Selection Tools
- •Creating Instance Variables in the Font Chooser
- •Writing the AssignFont() Method
- •Writing the Event Handlers
- •Working with Images and Scroll Bars
- •Setting Up the Picture Box
- •Adding a Scroll Bar
- •Revisiting the Visual Critter
- •Designing the Program
- •Determining the Necessary Tools
- •Designing the Form
- •Writing the Code
- •Summary
- •Chapter 7: Timers and Animation: The Lunar Lander
- •Introducing the Lunar Lander
- •Reading Values from the Keyboard
- •Introducing the Key Reader Program
- •Setting Up the Key Reader Program
- •Coding the KeyPress Event
- •Coding the KeyDown Event
- •Determining Which Key Was Pressed
- •Animating Images
- •Introducing the ImageList Control
- •Setting Up an Image List
- •Looking at the Image Collection
- •Displaying an Image from the Image List
- •Using a Timer to Automate Animation
- •Introducing the Timer Control
- •Configuring the Timer
- •Adding Motion
- •Checking for Keyboard Input
- •Working with the Location Property
- •Detecting Collisions between Objects
- •Coding the Crasher Program
- •Getting Values for newX and newY
- •Bouncing the Ball off the Sides
- •Checking for Collisions
- •Extracting a Rectangle from a Component
- •Getting More from the MessageBox Object
- •Introducing the MsgDemo Program
- •Retrieving Values from the MessageBox
- •Coding the Lunar Lander
- •The Visual Design
- •The Constructor
- •The timer1_Tick() Method
- •The moveShip() Method
- •The checkLanding() Method
- •The theForm_KeyDown() Method
- •The showStats() Method
- •The killShip() Method
- •The initGame() Method
- •Summary
- •Chapter 8: Arrays: The Soccer Game
- •The Soccer Game
- •Introducing Arrays
- •Exploring the Counter Program
- •Creating an Array of Strings
- •Referring to Elements in an Array
- •Working with Arrays
- •Using the Array Demo Program to Explore Arrays
- •Building the Languages Array
- •Sorting the Array
- •Designing the Soccer Game
- •Solving a Subset of the Problem
- •Adding Percentages for the Other Players
- •Setting Up the Shot Demo Program
- •Setting Up the List Boxes
- •Using a Custom Event Handler
- •Writing the changeStatus() Method
- •Kicking the Ball
- •Designing Programs by Hand
- •Examining the Form by Hand Program
- •Adding Components in the Constructor
- •Responding to the Button Event
- •Building the Soccer Program
- •Setting Up the Variables
- •Examining the Constructor
- •Setting Up the Players
- •Setting Up the Opponents
- •Setting Up the Goalies
- •Responding to Player Clicks
- •Handling Good Shots
- •Handling Bad Shots
- •Setting a New Current Player
- •Handling the Passage of Time
- •Updating the Score
- •Summary
- •Chapter 9: File Handling: The Adventure Kit
- •Introducing the Adventure Kit
- •Viewing the Main Screen
- •Loading an Adventure
- •Playing an Adventure
- •Creating an Adventure
- •Reading and Writing Text Files
- •Exploring the File IO Program
- •Importing the IO Namespace
- •Writing to a Stream
- •Reading from a Stream
- •Creating Menus
- •Exploring the Menu Demo Program
- •Adding a MainMenu Object
- •Adding a Submenu
- •Setting Up the Properties of Menu Items
- •Writing Event Code for Menus
- •Using Dialog Boxes to Enhance Your Programs
- •Exploring the Dialog Demo Program
- •Adding Standard Dialogs to Your Form
- •Using the File Dialog Controls
- •Responding to File Dialog Events
- •Using the Font Dialog Control
- •Using the Color Dialog Control
- •Storing Entire Objects with Serialization
- •Exploring the Serialization Demo Program
- •Creating the Contact Class
- •Referencing the Serializable Namespace
- •Storing a Class
- •Retrieving a Class
- •Returning to the Adventure Kit Program
- •Examining the Room Class
- •Creating the Dungeon Class
- •Writing the Game Class
- •Writing the Editor Class
- •Writing the MainForm Class
- •Summary
- •Chapter 10: Chapter Basic XML: The Quiz Maker
- •Introducing the Quiz Maker Game
- •Taking a Quiz
- •Creating and Editing Quizzes
- •Investigating XML
- •Defining XML
- •Creating an XML Document in .NET
- •Creating an XML Schema for Your Language
- •Investigating the .NET View of XML
- •Exploring the XmlNode Class
- •Exploring the XmlDocument Class
- •Reading an Existing XML Document
- •Creating the XML Viewer Program
- •Writing New Values to an XML Document
- •Building the Document Structure
- •Adding an Element to the Document
- •Displaying the XML Code
- •Examining the Quizzer Program
- •Building the Main Form
- •Writing the Quiz Form
- •Writing the Editor Form
- •Summary
- •Overview
- •Introducing the SpyMaster Program
- •Creating a Simple Database
- •Accessing the Data Server
- •Accessing the Data in a Program
- •Using Queries to Modify Data Results
- •Limiting Data with the SELECT Statement
- •Using an Existing Database
- •Adding the Capability to Display Queries
- •Creating a Visual Query Builder
- •Working with Relational Databases
- •Improving Your Data with Normalization
- •Using a Join to Connect Two Tables
- •Creating a View
- •Referring to a View in a Program
- •Incorporating the Agent Specialty Attribute
- •Working with Other Databases
- •Creating a New Connection
- •Converting a Data Set to XML
- •Reading from XML to a Data Source
- •Creating the SpyMaster Database
- •Building the Main Form
- •Editing the Assignments
- •Editing the Specialties
- •Viewing the Agents
- •Editing the Agent Data
- •Summary
- •List of Figures
- •List of Tables
- •List of Sidebars
Data Type Problems
To a human being, the integer 3 is just like the real number 3.0. However, in a computer system, the int value 3 is stored differently than the long value 3. The float and double versions of these numbers are even more different. The computer can convert between these types, but often with problems. Take a look at this segment of the Simple Math program:
//division by integers can cause problems Console.WriteLine("5/4 = {0}", 5 / 4);
In the corresponding output, you see a surprising result.
Output:
5/4 = 1
Of course, 5 divided by 4 equals 1.25, so something went wrong. C# recognizes that both 5 and 4 are integers, so it assumes that the result of any operation between them should also be an integer. I fixed this problem by forcing 4 and 5 to be read as floating−point variables, like this:
Console.WriteLine("5f/4f = {0}", 5f / 4f);
Math Operators
Now that you know how to represent numbers, you can do basic math on them. All the basic operators work as you might expect. The plus sign (+) is used for addition, the minus sign (−) for subtraction, the forward slash (/) for division, and the asterisk (*) for multiplication.
Converting Variables
Knowing how to convert variables from one data type to another is important for programmers. C# offers many ways to perform these conversions. Sometimes, as in the Simple Math program, the conversion is done automatically. Other times, you have to do the conversion explicitly. Fortunately, C# makes variable conversion easy. As usual, it makes sense to look at a working program (see Figure 2.4):
Figure 2.4: Although the console works only with string values, you can convert strings to whatever
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type of variable you wish.
using System;
namespace ConvertDemo
{
///<summary>
///demonstrates various types of variable conversions
///Andy Harris, 11/09/01
///</summary>
class ConvertDemo
{
static void Main()
{
int myInt; double myDouble; string myString;
myInt = 5;
//copying an int to a double causes no problems myDouble = myInt;
Console.WriteLine("myDouble is {0}.", myDouble);
//copying |
a double to an int won't |
work! |
|
myDouble = 3.5; |
|
|
|
//myInt = |
myDouble; |
//this line |
causes an error |
//Console.WriteLine(myInt); |
|
||
//You can |
explicitly cast, but you |
might lose data |
|
myInt = (int)myDouble; |
|
|
Console.WriteLine("After casting, myInt = {0}.", myInt);
myString = myDouble.ToString(); Console.WriteLine("myDouble as a String: {0}", myString);
Console.Write("Please enter a number: "); myString = Console.ReadLine();
Console.WriteLine("myString converted to double: {0}",
Convert.ToDouble(myString));
} // end main } // end class
}// end namespace
Trick Some programmers prefer some alternate syntaxes, such as myFloat.Parse(someString) or myInt.Parse(someString). However, the Convert syntax works on all variables types, so it’s a pretty convenient solution.
To illustrate some key conversion ideas, I created an int, a double, and a string. These are, by far, the most common variable types you will use. I started by assigning the value 5 (an integer value) to myInt. Then, I copied the value of myInt to the myDouble variable. This caused no problems because a double can easily hold all the information in an int. However, the next few lines of code assign the value 3.5 to myDouble and then try to copy the value of myDouble to myInt. In the preceding source code, I’ve placed the comment characters before this line so it will not execute. This is commonly called commenting out code.
I commented out that particular line of code because it causes the system to crash. You cannot copy a double value to an int because doubles have more information (namely, the information after the decimal point). You can’t even copy the value 3.0 to an int variable directly because 3.0 is a
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double value.
Explicit Casting
You can convert a double value to an integer value, but you will lose some information along the way. Take a look at this line:
myInt = (int)myDouble;
This line copies the value of myDouble to myInt successfully, but it does so by utilizing a trick called casting, in which the term (int) tells the compiler to convert the value immediately following into an integer value. This results in a loss of data, but it works. You can use this type of operation to convert any numeric data types.
The Convert Object
Strings are not like other types of data because the amount of information necessary to store a string can vary, based on the length of the string. You don’t have to worry about this, but you should know that the conversion techniques that work between numbers do not work the same way with string variables. The string value "123" is not the same as the int value 123 or the double value 123.0. You cannot use a casting operation to convert to or from a string value. Therefore,
myInt = (int)"123"
does not work, and
myString = (string) 123
does not work, either.
In the Real World
Converting numeric data to strings is important because all the user generally sees is text information. When the user types something, the program usually sees it as a string value. For example, the Console.ReadLine() method always results in a string value. If you want to get a number from the user, you have to take the string from the ReadLine() method and convert it to a number yourself.
Fortunately, C# has an object that specializes in converting variables between types, and it always works. The convert object, pictured in Figure 2.5, is a special object that provides several useful methods. Methods are actions an object can perform. Most of the convert object’s methods convert data from one type to another.
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Figure 2.5: The convert object can convert nearly any variable type to any other variable type.
The Convert class is part of the System namespace, so you already have access to it. To use the class, you call one of its methods. For example,
myInt = Convert.ToInt32("123");
converts the string value "123" into an integer and stores that value into myInt. Likewise, the statement
myString = Convert.ToString(123);
takes the int value 123 and converts it into a string for storage in the myString variable. Of course, you usually won’t use the Convert class with literal values, as I’ve done in these examples. Generally, you stuff a variable in the ToInt32() or ToString() method, like this:
myInt = Convert.ToInt32(myString);
Because you sometimes grab a numeric value from the console, you often simply put the Console.ReadLine() method inside the ToInt() parentheses, like this:
myInt = Convert.ToInt32(Console.ReadLine());
Trap The convert object isn’t foolproof. If you let the user type in data, you don’t have any way to know whether he or she added a decimal point. You might be tempted to write code like this: myInt = Convert.ToInt32(Console.ReadLine()); This code works great if the user types an integer, but if the user enters a real number with a decimal point, your program will crash. It is safer to do the same operation in two steps, like this: myDouble = Convert.ToDouble(Console.ReadLine()); myInt = (int)
myDouble; The compiler will have no problem converting a
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