jozef goetz, 2012 1 2009 pearson education, inc. all rights reserved. 2002 prentice hall. all...

Jozef Goetz, 2012

1

2009 Pearson Education, Inc. All rights reserved.

2002 Prentice Hall. All rights reserved.

expanded by J. Goetz, 2012

Jozef Goetz, 2012

2

When faced with a decision, I always ask, “What would be the most fun?”• Peggy Walker

What’s in a name? That which we call a roseby any other name would smell as sweet.• William Shakespeare

“Take some more tea,” the March Hare said to Alice, very earnestly. “I’ve had nothing yet.” Alice replied in an offended tone, “So I can’t take more.” “You mean you can’t take less,” said the Hatter, “it’s very easy to take more than nothing.” • Lewis Carroll

Jozef Goetz, 2012

3OBJECTIVES

In this chapter you will learn: To write simple C# applications using code rather than visual

programming. To write statements that input and output data to the screen. To declare and use data of various types. To store and retrieve data from memory. To use arithmetic operators.

• To determine the order in which operators are applied. To write decision-making statements. To use relational and equality operators. To use message dialogs to display messages.

Jozef Goetz, 2012

4

Chapter 3 – Introduction to C# Programming

Outline

3.1 Introduction

3.2 A Simple C# Application: Displaying a Line of Text

3.3 Creating Your Simple Application in Visual C# Express

3.4 Modifying Your Simple C# Application

3.5 Formatting Text with Console.Write and Console.Writeline

3.6 Another C# Application: Adding Integers

3.7 Memory Concepts

3.8 Arithmetic

3.9 Decision Making: Equality and Relational Operators

Jozef Goetz, 2012

53.1 Introduction

Console applications• No visual components

• Only text output

• Text output in a console application is displayed in a console window.

Two types of console window – Command Line Interfaces (CLI)

– MS-DOS prompt

• called in Windows 95/98/ME

– Command prompt

• called in windows 2000/NT/XP/Vista/Windows 7

Windows applications Forms with several output types (windows, dialogs, and so forth) Contain Graphical User Interfaces (GUIs)

Jozef Goetz, 2012

63.2 Simple Program: Printing a line of text

Comments• Comments can be created using //…• Multi-lines comments use /* … *//* This is a multiple

line comment. It can be split over many lines */

Comments are ignored by the compiler• Used only for human readers

Namespaces• Groups related fundamental classes and base

classes into categories• Allows the easy reuse of code• Many namespaces are found in the Framework Class Library (FCL)• Must be referenced in order to be used

White Space• Includes spaces, newline characters and tabs

2002 Prentice Hall.All rights reserved.

Outline7

Welcome1.cs

Program Output

1 // Fig. 3.1: Welcome1.cs2 // A first program in C#.3 4 using System;5 6 class Welcome17 {8 static void Main( string[] args )9 {10 Console.WriteLine( "Welcome to C# Programming!" );11 }12 }

Welcome to C# Programming!

This is the using directive. It lets the compiler know that it should include the System namespace.

This is the start of the Main method. In this case it instructs the program to do everything


Outline8

Welcome1.cs

Program Output

1 // Fig. 3.1: Welcome1.cs2 // A first program in C#.3 4 using System;5 6 public class Welcome17 {8 static void Main( string[] args )9 {10 Console.WriteLine( "Welcome to C# Programming!" );11 }12 }

Welcome to C# Programming!

Line 1, 2: These are two single line comments. They are ignored by the compiler and are only used to aid other programmers. They use the double slash (//)

This is the using directive. It lets the compiler know that it should include the System namespace.

Line3: This is a blank line. It means nothing to the compiler and is only used to add clarity to the program.

Line 6: This is the beginning of the Welcome1 class definition. It starts with the class keyword and then the name of the class followed by class bodies

This is the start of the Main method. In this case it instructs the program to do everything

This is a string of characters that Console.WriteLine instructs the compiler to output

Jozef Goetz, 2012

93.2 Simple Program: Printing a Line of Text

Fig. 3.3 Execution of the Welcome1 program.

Jozef Goetz, 2012


C# identifier• Series of characters consisting of letters, digits and

underscores ( _ ) • Does not begin with a digit, has no spaces• Examples: Welcome1, identifier, _value, button7 7button is invalid

• C# is case sensitive (capitalization matters) a1 and A1 are different

Blank line• Makes program more readable• Blank lines, spaces, and tabs are white-space characters• Ignored by compiler

6 class Welcome1

Jozef Goetz, 2012


Keywords• words reserved for use by C# e.g. public class• Words that cannot be used as variable or class names or any other

capacity• Have a specific unchangeable function within the language

– Example: class • All keywords are lowercase

Classes• Every C# program has at least one user-defined class• Class names can only be one word long (i.e. no white space in class

name )

• Class names are capitalized, capitalize every word– SampleClassName

• Each class name is an identifier

6 class Welcome1

Jozef Goetz, 2012


• Class bodies start with a left brace ({) class Welcome1 {

• Class bodies end with a right brace (})

Methods• Building blocks of programs

– C# applications contain one or more methods• Methods can perform tasks and return information

void means Main returns no information

• The Main method Each console or windows application must have exactly

one All programs start by executing the Main method (in Java main() ) –

only a lower case difference)– static void Main( string[] args )

• Braces are used to start ({) and end (}) a method body

Jozef Goetz, 2012


Statements• Instructs computer to perform an action

• Anything in quotes (“) is considered a string including white spaces

• Every statement must end in a semicolon (;)

Prints string of characters

– String: series characters inside double quotes White-spaces in strings are not ignored by compiler

• Method Console.WriteLine Standard output Print to command window (i.e., MS-DOS prompt) Displays line of text

10 Console.WriteLine( "Welcome to C# Programming!" );

Jozef Goetz, 2012


Graphical User Interface• GUIs are used to make it easier to get data from the user as

well as display data to the user

• Message boxes Within the System.Windows.Forms namespace Used to prompt or display information to the user

Jozef Goetz, 2012

15Common Programming Error 3.1

Forgetting one of the delimiters of a delimited comment is a syntax error.

The syntax of a programming language specifies the rules for creating a proper application in that language.

A syntax error occurs when the compiler encounters code that violates C#’s language rules. • In this case, the compiler does not produce an executable file.

• Instead, the compiler issues one or more error messages to help you identify and fix the incorrect code.

Syntax errors are also called compiler errors, compile-time errors or compilation errors, because the compiler detects them during the compilation phase. • You will be unable to execute your application until you

correct all the syntax errors in it.

Jozef Goetz, 2012


Keyword: using A using directive tells the compiler where to look for a

predefined class that is used in an application.

Predefined classes are organized under namespaces—named collections of related classes.

• Collectively, .NET’s namespaces are referred to as the .NET Framework Class Library.

The System namespace contains the predefined Console class and many other useful classes.

All using directives must appear before any other code (except comments) in a C# source code file;

• otherwise a compilation error occurs.

Jozef Goetz, 2012

17Error-Prevention Tip 3.1

Forgetting to include a using directive for a class used in your application typically results in a compilation error

• containing a message such as "The name

'Console' does not exist in the current context."

When this occurs, check that you provided the proper using directives and that the names in the using directives are spelled correctly, including proper use of uppercase and lowercase

letters.

Jozef Goetz, 2012

18

C# Keywords

abstract as base bool break byte case batch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach goto if implicit in int interface internal is lock long namespace new null object operator out override params private protected public readonly ref return sbyte sealed short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushort using virtual void volatile while

Fig. 3.2 | C# keywords.

Jozef Goetz, 2012

19

Good Programming Practice 3.1

By convention, always begin a class name’s identifier with a capital letter and start each subsequent word in the identifier with a capital letter.

public class MyClass { … }

Jozef Goetz, 2012


C# is case sensitive. • Not using the proper uppercase and lowercase letters for an

identifier normally causes a compilation error.

• Identifiers may also be preceded by the @ character. This indicates that a word should be interpreted as an identifier, even if it is a keyword (e.g. @int).

By convention, a file that contains a single public class should have a name that is identical to the class name (plus the .cs extension) • Naming your files in this way makes it easier for other

programmers (and you) to determine where the classes of an application are located.

Good Programming Practice 3.2

Jozef Goetz, 2012

21Good Programming Practice 3.5

We recommend using 3 spaces to form each level of indentation.

As with class declarations, indent the entire body of each method declaration one “level” of indentation between the left and right braces that define the method body. • This format makes the structure of the method stand out and makes the method

declaration easier to read.• You can let the IDE format your code by selecting Edit > Advanced >

Format Document

Jozef Goetz, 2012

22Common Programming Error

Omitting the semicolon at the end of a statement is a syntax error.

Exc.1: Try removing a semicolon or brace from the code of Fig. 3.1, then recompiling the application to see the error messages generated by the omission.

Jozef Goetz, 2012

23Error-Prevention Tip

When the compiler reports a syntax error, the error may not be in the line indicated by the error message.

First, check the line for which the error was reported.

If that line does not contain syntax

errors, check several preceding lines.

Jozef Goetz, 2012

24Good Programming Practice

Following the closing right brace of a method body or class declaration with a comment indicating the method or class declaration to which the brace belongs

improves application readability.

} // end method Main

Jozef Goetz, 2012

25

3.2 A Simple C# Application: Displaying a Line of Text (Cont.)

.

Error-Prevention Tip 3.2

Whenever you type an opening left brace, {, in your application, immediately type the closing right brace, }, then reposition the cursor between the braces and indent to begin typing the body.

This practice helps prevent errors due to missing braces.

Jozef Goetz, 2012

26

3.2 A Simple C# Application: Displaying a Line of Text (Cont.)

Parentheses after an identifier indicate that it is an application building block called a method. Class declarations normally contain one or more methods.

Console.WriteLine( "Welcome to C# Programming!" )

Method names usually follow the same casing capitalization conventions used for class names.

For each application, one of the methods in a class must be called Main; otherwise, the application will not execute.

Methods are able to perform tasks and return information when they complete their tasks. • Keyword void indicates that this method will not return any

information after it completes its task.

Jozef Goetz, 2012

273.3 Creating Your Simple Application in Visual C# Express

1. Creating the Console Application• Select File > New Project… to display the New Project dialog

(Fig. 3.3).

• Select the Console Application template.

• In the dialog’s Name field, type Welcome1, and click OK to create the project.

2. Modifying the Editor Settings• Visual C# Express provides many ways to personalize your coding

experience (Fig. 3.5)

• e.g. tab setup: Tools->Options->Text Editor -> Tabs

3. Changing the Name of the Application File• Change the File Name property to Welcome1.cs.

(Fig. 3.6)

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28

Fig. 3.3 | Creating a Console Application with the New Project dialog.

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29

3.3 Creating a Simple Application in Visual C# Express (Cont.)

The IDE now contains the open console application.

The code coloring scheme used by the IDE is called syntax-color shading and helps you visually differentiate application elements.

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30


Fig. 3.4 | IDE with an open console application.

Editor window

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31

Fig. 3.5 | Modifying the IDE settings.

tab setup: Tools->Options->Text Editor -> Tabs

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32

Fig. 3.5 | Modifying the IDE settings.

To have the IDE display line numbers, select Tools > Options….• In the dialog that appears (Fig. 3.5), click the Show all settings checkbox on

the lower left of the dialog.

• Expand the Text Editor node in the left pane and select All Languages. On the right, check the Line numbers checkbox.

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33

Solution Explorer

Properties window

File Name Property

Click Program.cs to

display its properties

Type Welcome1.cs here

to rename the file

Fig. 3.6 | Renaming the program file in the Properties window.

1. Changing the Name of the Application FileChange the File Name property to Welcome1.cs.

Jozef Goetz, 2012

343.3 Creating Your Simple Application in Visual C# Express (Cont.)

4. Writing Code• IntelliSense: Lists a class’s members after a dot (Fig. 3.7-3.8)

5. Saving the Application• Specify the directory where you want to save this project (Fig.

3.9)

6. Compiling and Running the Application• Compiler compiles code into files (Fig. 3.10)

Ex: .exe (executable), .dll (dynamic link library), and more!

7. Running the Application from the Command Prompt• Alternate way to go run a program without using the IDE (Fig.

3.11-3.12)

Jozef Goetz, 2012

35

Partially-typed member

Member list

Highlighted member

Tool tip describeshighlighted member

Fig. 3.7 | IntelliSense feature of Visual C# Express.

Jozef Goetz, 2012

363.3 Creating a Simple Application in

Visual C# Express (Cont.) IntelliSense lists a class’s members, which include method

names. As you type characters, Visual C# Express highlights the

first member that matches all the characters typed, then displays a tool tip containing a description of that member.

You can either type the complete member name, double click the member name in the member list or press the Tab key to complete the name.

While the IntelliSense window is displayed pressing the Ctrl key makes the window transparent so you can see the code behind the window.

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37


When you type the open parenthesis character, (, after a method name, the Parameter Info window is displayed (Fig. 3.8).

This window contains information about the method’s parameters.

Down arrow Parameter Info window

Up arrow

Fig. 3.8 | Parameter Info window.

• Up and down arrows allow you to scroll through overloaded versions of the method.

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38


To save an application, select File > Save All to display the Save Project dialog (Fig. 3.9).

In the Location textbox, specify the directory where you want to save this project.

Select the Create directory for solution checkbox and click Save.

Fig. 3.9 | Save Project dialog.

Jozef Goetz, 2012

39

Console window

Fig. 3.10 | Executing the application shown in Fig. 3.11

To compile an application, select Build > Build Solution. To execute it, select Debug > Start Without

Debugging (or type Ctrl + F5).• This invokes the Main method.

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40


Running (outside the IDE) the Application from the Command Prompt

To open the Command Prompt, select Start > All Programs > Accessories > CommandPrompt.

Fig. 3.11 | Command Prompt window when it is initially opened.

Default prompt displays whenCommand Prompt is opened

User enters the next command here

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41


To Enter the command cd (which stands for “change directory”), followed by the directory where the application’s .exe file is located

Run the compiled application by entering the name of the .exe file.

Fig. 3.12 | Executing the application shown in Fig. 3.1 from aCommand Prompt window.

Updated prompt showingthe new current directory

Type this to change to theapplication’s directory

Application’s output Closes the Command PromptType this to run the Welcome1.exe application

Jozef Goetz, 2012

423.3 Creating Your Simple Application in Visual C# Express (Cont.)

Syntax Errors, Error Messages and the Error List Window

• Syntax Error A violation of Visual C# rules for creating correct application

• Error List Window (Fig. 3.13) Window where the descriptions of the errors are located

Note: Red underline indicts a syntax error

Jozef Goetz, 2012

43

Intentionally omitted parenthesis character (syntax error)

Red underline indicates a syntax errorError List window

Error description(s)

Fig. 3.13 | Syntax errors indicated by the IDE.

Jozef Goetz, 2012

44Error-Prevention Tip 3.5

Exc2: Remove the 1st parenthesis in line 10.• What happens?

The compiler thinks there are 2 statements.

One syntax error can lead to multiple entries in the Error List window.

Each error that you address could eliminate several subsequent error messages when you recompile your application.

So when you see an error you know how to fix, correct it and recompile — this may make several other errors disappear.

Jozef Goetz, 2012

45

• Class Welcome2, shown in Fig. 3.14, uses two statements to produce the same output as that shown in the previous example.

• Unlike WriteLine, the Console class’s Write method does not position the screen cursor at the beginning of the next line in the console window.

3.4 Modifying Your Simple C# Application

Jozef Goetz, 2012

46 1 // Fig. 3.14: Welcome2.cs

2 // Printing one line of text with multiple statements.

3 using System;

4

5 public class Welcome2

6 {

7 // Main method begins execution of C# application

8 public static void Main( string[] args )

9 {

10 Console.Write( "Welcome to " );

11 Console.WriteLine( "C# Programming!" );

12 } // end method Main

13 } // end class Welcome2 Welcome to C# Programming!

Outline

Welcome2.cs

Cursor stays on same line after outputting

Cursor moves to next line after outputting

Console.WriteLine will pick up where the line ends. This will cause the output to be on one line even though it is on two in the code.

Jozef Goetz, 2012

473.4 Modifying Your Simple C# Application (Cont.)

Escape characters• Backslash ( \ )

• Indicates special characters be output

Newline characters (\n)• Interpreted as “special characters” by methods Console.Write and Console.WriteLine

• Indicates cursor should be at the beginning of the next line

• Welcome3.cs (Fig. 3.15)

• Line breaks at \n

10 Console.WriteLine( “Welcome\nto\nC#\nProgramming!" );

Jozef Goetz, 2012


2 // Printing multiple lines with a single statement.

3 using System;

4


6 {



9 {

10 Console.WriteLine( "Welcome\nto\nC#\nProgramming!" );



Welcome3.cs

Notice how a new line is output for each \n escape sequence.

The \n escape sequence is used to put output on the next line. This causes the output to be on several lines even though it is only on one in the code.

Jozef Goetz, 2012


Escape sequence Description \n Newline. Position the screen cursor to the beginning of the

next line. \t Horizontal tab. Move the screen cursor to the next tab stop. \r Carriage return. Position the screen cursor to the beginning

of the current line; do not advance to the next line. Any characters output after the carriage return overwrite the previous characters output on that line.

\\ Backslash. Used to print a backslash character. \" Double quote. Used to print a double quote (") character. Fig. 3.16 Some common escape sequences.

Jozef Goetz, 2012


2 // Printing multiple lines of text with string formatting.

3 using System;

4


6 {



9 {

10 Console.WriteLine( "{0}\n{1}", "Welcome to", "C# Programming!" );



Outline

Welcome4.cs

Formatting Text Place a space after each comma (,) in an argument

list to make applications more readable.

Splitting a statement in the middle of an identifier or a string is a syntax error.

Method WriteLine’s first argument is a format string

that may consist of fixed text and format items.

Jozef Goetz, 2012

513.5 Formatting Text with Console.Write and Console.WriteLine

Formatted Data

• Arguments are separated with commas

• WriteLine’s first argument is format string Format items: Placeholder for a value

– {0} is a placeholder for the first additional argument.

– {1} is a placeholder for the second, and so on.

• Fixed text: Regular text that is outputted

10 Console.WriteLine( “{0}\n{1}”, “Welcome to”, “C# Programming” );


Outline52

Welcome4.cs

Program Output

1 // Fig. : Welcome5.cs ed1.2 // Printing multiple lines in a dialog Box.3 4 using System;5 using System.Windows.Forms;6 7 class Welcome48 {9 static void Main( string[] args )10 {§ MessageBox.Show( "Welcome\nto\nC#\nprogramming!" ); // static method of class MessageBox // static methods called using class name, dot (.) then method name

12 }13 }

The System.Windows.Forms namespace allows the programmer to use the MessageBox class.

This will display the contents in a message box as opposed to in the console window.

Create the GUI output

Jozef Goetz, 2012

53Simple Program: Printing a Line of Text

Fig. Dialog displayed by calling MessageBox.Show.

OK button allows the user to dismiss the dialog.

Dialog is automatically sized to accommodate its contents.

Mouse cursor

Close box

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54

Namespaces• Groups related C# fundamental classes and base classes into a

categories The assembly is package containing the Microsoft intermediate Language

(MSIL) code

• that a project has been compiled into, plus other info that is needed for these classes

• Assemblies can be comprised of many files of several different types

MessageBox is located in assembly System.Windows.Forms.dll

Developer for the appl. needs to include:

• namespaces with the using directive (package in Java) and • references

click the References folder in the solution Explorer and select Add References and select component from the dialog box by double clicking, then click OK

– VS adds a few common references when a project is created• Class Console is located in mscorlib.dll• Class MessageBox is located System.Windows.Forms.dll

(see C:\WINDOWS\Microsoft.Net\Framework\v4.0.30319 for above .dlls or select another version number) but a reference to mscorlib.dll assembly is not required to use it

Jozef Goetz, 2012


References folder

Solution Explorer

System.Windows.Forms reference

Fig. Adding a reference to an assembly in Visual Studio .NET (part 2).

Jozef Goetz, 2012


Fig. Adding a reference to an assembly in Visual Studio .NET (part 1).

Add Reference dialogue

Jozef Goetz, 2012

573.6 Another Simple Program: Adding Integers

Primitive data types• Data types that are built into C#

String, Int, Double, Char, Long 15 primitive data types (chapter 4)

• Each data type name is a C# keyword

• Same type variables can be declared on separate lines or on one line

Console.ReadLine()• Used to get a value from the user input

Int32.Parse() or Convert.ToInt32()• Used to convert a string argument to an integer

• Allows math to be preformed once the string is converted

Jozef Goetz, 2012

58Convention

Begin with a lowercase letter and capitalize each successive English letter for identifiers representing variables.

• middleInitial, myName.

This naming convention is known as camel casing.

Jozef Goetz, 2012

59 1 // Fig. 3.18: Addition.cs

2 // Displaying the sum of two numbers input from the keyboard.

3 using System;

4

5 public class Addition

6 {



9 {

10 int number1; // declare first number to add

11 int number2; // declare second number to add

12 int sum; // declare sum of number1 and number2

13

14 Console.Write( "Enter first integer: " ); // prompt user

15 // read first number from user

16 number1 = Convert.ToInt32( Console.ReadLine() );

17

18 Console.Write( "Enter second integer: " ); // prompt user

19 // read second number from user

20 number2 = Convert.ToInt32( Console.ReadLine() );

21

22 sum = number1 + number2; // add numbers

23

24 Console.WriteLine( "Sum is {0}", sum ); // display sum


26 } // end class Addition Enter first integer: 45 Enter second integer: 72 Sum is 117

This is the well commented program with comment indented.

Outline

Addition.cs

using declaration imports necessary components from the System namespace.

Declare variables number1, number2 and sum.

Convert user’s input into an int, and assign it to number1.

Convert user’s next input into an int, and assign it to number2.

Calculate the sum of the variables number1 and number2, assign result to sum.

Display the sum using formatted output.

Jozef Goetz, 2012

603.6 Another C# Application: Adding Integers

• Begins public class Addition Recall that file name must be Addition.cs

• Lines 8-9: begins Main

• Variables Location in memory that stores a value

– Declare with name and type before use Variable name: any valid identifier

• Declarations end with semicolons ;• Initialize variable in its declaration

Equal sign

5 public class Addition 6 {

8 public static void Main( string[] args) 9 {

Jozef Goetz, 2012

613.6 Another C# Application: Adding Integers (Cont.)

• Declare variable number1, number2 and sum of type int int holds integer values (whole numbers): i.e., 0, -4, 97 Types float, double and decimal can hold decimal numbers Type char can hold a single character: i.e., x, $, \n, 7 int, float, double, decimal and char are simple types

• Can add comments to describe purpose of variables

• Can declare multiple variables of the same type in one declaration Use comma-separated list

10 int number1; // first number to add11 int number2; // second number to add12 int sum; // second number to add

int number1, // first number to add number2, // second number to add sum; // second number to add

Jozef Goetz, 2012


Choosing meaningful variable names helps code to be self-documenting • i.e., one can understand the code simply by

reading it rather than by reading documentation manuals or viewing an excessive number of comments.

Jozef Goetz, 2012


• Similar to previous statement Prompts the user to input the second integer

• Similar to previous statement Assign variable number2 to second integer input

• Assignment statement Calculates sum of number1 and number2 (right hand side) Uses assignment operator = to assign result to variable sum Read as: sum gets the value of number1 + number2 number1 and number2 are operands

18 Console.Write( "Enter second integer: " ); // prompt user

20 number2 = Convert.ToInt32( (Console.ReadLine() );

22 sum = number1 + number2; // add numbers

Jozef Goetz, 2012


• Use Console.WriteLine to display results

• {0} is placeholder for sum

• Calculations can also be performed inside WriteLine

• Parentheses around the expression number1 + number2 are not required

24 Console.WriteLine( "Sum is {0}: " , sum ); // display sum

Console.WriteLine( "Sum is {0} " , ( number1 + number2 ) );


Outline65

Addition.cs

1 // Fig. 3.11: ed2. Addition.cs. Well commented program with comment indented.2 // An addition program.3 4 using System;5 6 class Addition7 {8 static void Main( string[] args )9 { // the sinle-line comments to indicate the purpose of each variable10 string firstNumber, // first string entered by user11 secondNumber; // second string entered by user12 13 int number1, // first number to add14 number2, // second number to add15 sum; // sum of number1 and number216 17 // prompt for and read first number from user as string18 Console.Write( "Please enter the first integer: " );19 firstNumber = Console.ReadLine();20 21 // read second number from user as string22 Console.Write( "\nPlease enter the second integer: " );23 secondNumber = Console.ReadLine(); // an assignment statement24 // = a binary operator 25 // convert numbers from type string to type int26 number1 = Int32.Parse( firstNumber ); // or use Convert.ToInt32()27 number2 = Int32.Parse( secondNumber );28 29 // add numbers30 sum = number1 + number2; // Read as: sum gets the value of number1 + number2

31

This is the start of class Addition

Two string variables defined over two lines

The comment after the declaration is used to briefly state the variable purpose

These are three ints that are declared over several lines and only use one semicolon. Each is separated by a coma.

Console.ReadLine is used to take the users input and place it into a variable.

This line is considered a prompt because it asks the user to input data.

Int32.Parse() or Convert.ToInt32() is used to convert the given string into an integer. It is then stored in a variable.

// Place spaces on either side of a binary operator to make it stand out and make the code more readable – see line 30


Outline66

Addition.cs

Program Output

32 // display results33 Console.WriteLine( "\nThe sum is {0}.", sum );34 35 } // end method Main36 37 } // end class Addition

Please enter the first integer: 45 Please enter the second integer: 72 The sum is 117.

Putting a variable out through Console.WriteLine is done by placing the variable after the text while using a placeholder { a number in curly braces} to show where the variable should be placed.

Declare each variable on a separate line. This format allows a comment to be easily inserted next to each declaration. See line 13-15

Jozef Goetz, 2012

673.7 Memory Concepts

Memory locations Variables

• Every variable has 1. a name,

2. a type,

3. a size and

4. a value

• Name corresponds to location in memory

• When new value is placed into a variable, replaces (and destroys) previous value

• Reading variables from memory does not change them

Jozef Goetz, 2012


Fig. 3.19 Memory location showing name and value of variable number1. 45 is replaced the previous value; previous value is destroyed

number1 45

Jozef Goetz, 2012


Fig. 3.20 Memory locations number1 and number2 after values for variables number1 and number2 have been input.

number1 45

number2 72

Jozef Goetz, 2012


Fig. 3.21 Memory locations after a calculation. When a sum is read from a memory , the process is nondestructive.

number1 45

number2 72

sum 117

Jozef Goetz, 2012

713.8 Arithmetic

Arithmetic operations• Not all operations use the same symbol

Asterisk (*) is multiplication Slash (/) is division Percent sign (%) is the modulus operator:

7 % 5 evaluates to 2 Plus (+) and minus (-) are the same

• Must be written in a straight line• There are no exponents

Division• Division can vary depending on the variables used

When dividing two integers the result is always rounded down to an integer

7 / 5 evaluates to 1

Tip: To be more exact use a variable that supports decimals

Jozef Goetz, 2012

723.8 Arithmetic

Order (Operator precedence):1. Parenthesis are done first

2. Division, multiplication and modulus are done second Left to right

3. Addition and subtraction are done last Left to right

Use parenthesis when needed or for clarity

• Example: Find the average of three variables a, b and c Do not use: a + b + c / 3 Use: ( a + b + c ) / 3

Jozef Goetz, 2012

733.8 Arithmetic

C# operation Arithmetic operator Algebraic expression C# expression

Addition + f + 7 f + 7

Subtraction – p – c p - c

Multiplication * bm b * m

Division / x / y or x / y

Modulus % r mod s r % s

Fig. 3.22 Arithmetic operators.

xy

Jozef Goetz, 2012

743.8 Arithmetic

Operator(s) Operation Order of evaluation (precedence) ( ) Parentheses Evaluated first. If the parentheses are

nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.

*, / or % Multiplication Division Modulus

Evaluated second. If there are several such operators, they are evaluated left to right.

+ or - Addition Subtraction

Evaluated last. If there are several such operators, they are evaluated left to right.

Fig. 3.23 Precedence of arithmetic operators.

Jozef Goetz, 2012

753.8 Arithmetic

Fig. 3.24 Order in which a second-degree polynomial is evaluated.

Exc: Show the order for z = p*r % w/x - y

Step 1.

Step 2.

Step 5.

Step 3.

Step 4.

Step 6.

y = 2 * 5 * 5 + 3 * 5 + 7;

2 * 5 is 10 (Leftmost multiplication)

y = 10 * 5 + 3 * 5 + 7;

10 * 5 is 50 (Leftmost multiplication)

y = 50 + 3 * 5 + 7;3 * 5 is 15 (Multiplication before addition)

y = 50 + 15 + 7;

50 + 15 is 65 (Leftmost addition)

y = 65 + 7;

65 + 7 is 72 (Last addition)

y = 72; (Last operation—place 72 into y)

Jozef Goetz, 2012


The if structure• Used to make a decision based on the truth of the

condition True: a statement is performed False: the statement is skipped over

Jozef Goetz, 2012


if control structure• Simple version in this section, more detail later• If a condition is true, then the body of the if statement

executed 0 interpreted as false, non-zero is true

• Control always resumes after the if structure• Conditions for if structures can be formed using equality or

relational operators (next slide)**************************************************if ( condition )

statement //executed if condition true

***************************************** No semicolon needed after condition

– Else conditional task not performed

Jozef Goetz, 2012


Standard algebraic equality operator or relational operator

C# equality or relational operator

Example of C# condition

Meaning of C# condition

Equality operators == x == y x is equal to y != x != y x is not equal to y Relational operators > > x > y x is greater than y < < x < y x is less than y >= x >= y x is greater than or equal to y <= x <= y x is less than or equal to y Fig. 3.25 Equality and relational operators.

Jozef Goetz, 2012


• if structure to test for equality using (==)

If variables equal (condition true) –number1 concatenated using + operator

if ( number1 == number2 )

Console.WriteLine( number1 + " == " + number2 );

string = number1 + other strings– Right side evaluated first, new string assigned to string


Outline80

Comparison.cs

1 // Fig. 3.26: Comparison.cs ed1.2 // Using if statements, relational operators and equality3 // operators.4 5 using System;6 7 class Comparison8 {9 static void Main( string[] args )10 { // multiple declaration for same type11 int number1, // first number to compare12 number2; // second number to compare13 14 // read in first number from user15 Console.Write( "Please enter first integer: " );16 number1 = Int32.Parse( Console.ReadLine() ); // or number1 = Convert.ToInt32( Console.ReadLine() );

18 // read in second number from user19 Console.Write( "\nPlease enter second integer: " );20 number2 = Int32.Parse( Console.ReadLine() );21 22 if ( number1 == number2 )23 Console.WriteLine( number1 + " == " + number2 ); //or Console.WriteLine( "{0} == {1}", number1, number2 );

25 if ( number1 != number2 )26 Console.WriteLine( number1 + " != " + number2 );27 28 if ( number1 < number2 )29 Console.WriteLine( number1 + " < " + number2 );30 31 if ( number1 > number2 )32 Console.WriteLine( number1 + " > " + number2 );33

Combining these two methods eliminates the need for a temporary string variable.

Please enter first integer: 2000 Please enter second integer: 10002000 != 10002000 > 10002000 >= 1000


Outline81

Comparison.cs

Program Output

34 if ( number1 <= number2 )35 Console.WriteLine( number1 + " <= " + number2 );36 37 if ( number1 >= number2 )38 Console.WriteLine( number1 + " >= " + number2 );39 40 } // end method Main41 42 } // end class Comparison

Please enter first integer: 2000 Please enter second integer: 10002000 != 10002000 > 10002000 >= 1000

Please enter first integer: 1000 Please enter second integer: 20001000 != 20001000 < 20001000 <= 2000

Please enter first integer: 1000 Please enter second integer: 10001000 == 10001000 <= 10001000 >= 1000

If number1 is less than or equal to number2 then this code will be used

Lastly if number1 is greater than or equal to number2 then this code will be executed

Jozef Goetz, 2012


Omitting the left and/or right parentheses for the condition in an if statement is a syntax error — the parentheses are required.

if ( number1 > number2 )

Console.WriteLine( number1 + " > " + number2 );

Jozef Goetz, 2012

83Common Programming Error

Confusing the equality operator, ==, with the assignment operator, =, can cause a logic error or a syntax error.

The equality operator should be read as “is equal to,” and the assignment operator should be read as “gets” or “gets the value of.”

To avoid confusion, some people read the equality operator as “double equals” or “equals equals.”

Jozef Goetz, 2012


Indent an if statement’s body to make it stand out and to enhance application readability.

if ( number1 > number2 )

Console.WriteLine( number1 + " > " + number2 );

Placing a semicolon immediately after the right parenthesis of the condition in an if statement is normally a logic error.

Jozef Goetz, 2012


Place one statement per line in an application. This format enhances readability.

Jozef Goetz, 2012


A lengthy statement can be spread over several lines. If a single statement must be split across lines,

• choose breaking points that make sense, such as after a comma in a comma-separated list, or after an operator in a lengthy expression.

If a statement is split across two or more lines, indent all subsequent lines until the end of the statement.

if ( studentGrade >= 90 ) Console.WriteLine( "A" );

else if ( studentGrade >= 80 ) Console.WriteLine( "B" );

Jozef Goetz, 2012

873.9 Decision Making: Equality and

Relational Operators in decreasing order of precedence

Operators Associativity Type () left to right parentheses * / % left to right multiplicative + - left to right additive < <= > >= left to right relational == != left to right equality = right to left assignment Fig. 3.27 Precedence and associativity of operators discussed in this

chapter.

Example:

x = y = 0 is evaluated as if were written x = (y = 0)

and later the result of (y = 0) is 0 assigned to x

If you are uncertain about the order of evaluation in a complex expression, use parentheses to force the order, as you would do in algebraic expressions. Observe that some operators, such as assignment, =, associate from right to left rather than from left to right.

if ( x > 5 ) { if ( y > 5 ) Console.WriteLine("x and y are > 5" ); } else Console.WriteLine( "x is <= " );

jozef goetz, 2012 1 2009 pearson education, inc. all rights reserved. 2002 prentice hall. all...

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