Jozef Goetz, 2012 1 2011 Pearson Education, Inc. All rights reserved. 2002 Prentice Hall. All...

Jozef Goetz, 2012

1

2011 Pearson Education, Inc. All rights reserved.

2002 Prentice Hall. All rights reserved.

expanded by J. Goetz, 2012

Jozef Goetz, 2012

2

Not everything that can be counted counts, and not every thing that counts can be counted. Albert Einstein

Who can control his fate? William Shakespeare

The used key is always bright. Benjamin Franklin

Jozef Goetz, 2012

3

Every advantage in the past is judged in the light of the final issue. Demosthenes

Intelligence …is the faculty of making artificial objects, especially tools to make tools. Henri Bergson

Jozef Goetz, 2012

4Objectives

The essentials of counter-controlled repetition. To be able to use the for and do/loop while

repetition structures to execute statements in a program repeatedly.

To understand multiple selection that uses the switch selection structure.

To be able to use the break and continue program-control statements.

To be able to use the logical operators.

Jozef Goetz, 2012

5

Chapter 6 – Control Structures: Part 2

6.1 Introduction 6.2 Essentials of Counter-Controlled Repetition 6.3 for Repetition Statement 6.4 Examples Using the for Statement 6.5 do…while Repetition Statement 6.6 switch Multiple-Selection Statement 6.7 break and continue Statements 6.8 Logical Operators 6.9 Structured Programming Summary 6.10 (Optional) Software Engineering Case Study:

Identifying Objects’ States and Activities in the ATM System

6.11 Wrap-Up

Jozef Goetz, 2012

66.1 Introduction

Before writing program Have thorough understanding of problem Carefully planned approach for solving it

While writing program Know what “building blocks” are available Use good programming principles

Continue structured-programming discussion Introduce C#’s remaining control structures

Jozef Goetz, 2012

76.2 Essentials of Counter-Controlled Repetition

Counter-controlled repetition (CCR) requires: Name of a control variable (loop counter) Initial value Condition to test for the final value (whether looping should

continue) Increment (or decrement)

Control variable modified each time through the loop

Upcoming example Counter-controlled repetition

2002 Prentice Hall.All rights reserved.

Outline8

WhileCounter.cs

Program Output

1 // Fig. 6.1: WhileCounter.cs2 // Counter-controlled repetition.3 4 using System;5 6 class WhileCounter7 {8 static void Main( string[] args )9 {10 int counter = 1; // 1 initialization11 12 while ( counter <= 5 )// 2 repetition condition13 {14 Console.WriteLine("{0}”,counter );15 counter++; // 3 increment16 17 } // end while18 19 } // end method Main20 21 } // end class WhileCounter

12345

This is where the counter variable is initialized. It is set to 1.

The loop will continue until counter is greater than five (it will stop once it gets to six)

The counter is incremented and 1 is added to it

Jozef Goetz, 2012

96.2 Essentials of Counter Controlled Repetition

Loop can be shortened Initialize counter to zero

Change loop to:

while ( ++counter <= 5 ) //repetition condition

Console.WriteLine( counter );

The precedence of ++ is higher that of <=

Good Programming Practice: Programs should control counting loops with

integer values. Indent the body; a blank line before & after control structure; avoid more than 3 level of nesting;

Jozef Goetz, 2012

10Common Programming Error 6.1

Because floating-point values may be approximate, controlling loops with floating-point

variables may result in imprecise counter values and inaccurate termination tests.

Jozef Goetz, 2012

116.3 for Repetition Structure

for ( int counter = 1; counter <= 5; counter++ )

Initial value of control variable Increment of control variable

Control variable name Final value of control variablefor keyword

Loop-continuation condition (test)

Fig. 6.3 Components of a typical for header.

•Handles counter-controlled-repetition details

Jozef Goetz, 2012


The for repetition structure Syntax: for (Expression1; Expression2; Expression3)

Expression1 = names the control variable– Can contain several variables

Expression2 = loop-continuation condition Expression3 = incrementing/decrementing

– If Expression1 has several variables, Expression3 must have several variables accordingly

– ++counter and counter++ are equivalent

for ( int counter = 1; counter <= 5; counter++ )

Variable scope Expression1 can only be used in the body of the for loop When the loop ends the variable counter expires

Jozef Goetz, 2012


counter++

Establish initial value of control variable.

Determine if final value of control variable has been reached.

counter <= 5

Console.WriteLine( counter * 5 );

true

false

counter = 1

Body of loop (this may be multiple statements)

Increment the control variable.

Fig. 6.4 Flowcharting a typical for repetition structure.

10 int counter = 1; // 1 initialization11 12 while ( counter <= 5 )// 2 repetition condition13 {14 Console.WriteLine("{0}”,counter );15 counter++; // 3 increment16 17 } // end while

Jozef Goetz, 2012

14 1 // Fig. 6.2: ForCounter.cs

2 // Counter-controlled repetition with the for repetition statement.

3 using System;

4

5 public class ForCounter

6 {

7 public static void Main( string[] args )

8 {

9 // for statement header includes initialization,

10 // loop-continuation condition and increment

11 for ( int counter = 1; counter <= 5; counter++ )

12 Console.Write( "{0} ", counter );

13

14 Console.WriteLine(); // output a newline

15 } // end Main

16 } // end class ForCounter 1 2 3 4 5

Outline

ForCounter.cs

Control-variable name is counter

Control-variable initial value is 1

Condition tests for counter’s final value

Increment for counter


Outline15

ForCounter.cs

Program Output

1 // Fig. 6.2: ForCounter.cs2 // Counter-controlled repetition with the for structure.3 4 using System;5 6 class ForCounter7 {8 static void Main( string[] args )9 {10 // initialization, repetition condition and incrementing11 // are all included in the for structure12 for ( int counter = 1; counter <= 5; counter++ )13 Console.WriteLine( “{0}”, counter );14 }15 }

12345

Fig. 6.4 | UML activity diagram for the for statement in Fig. 6.2.

Jozef Goetz, 2012

166.3 The for Repetition Structure (cont.)

Good Programming Practices Place only expressions involving the control variables in the

initialization and increment sections of a for structure. Manipulations of other control variables should appear

either before the loop (if they execute only once, like initialization

statements) or in the body of the loop (if they execute once per iteration of

the loop, like incrementing or decrementing statements).

Common Programming Errors 6.2 When the control variable of a for structure is initially

defined in the initialization section of the header of the for structure, using the control variable after the for’s body is a compilation error (the control variable expires).

Jozef Goetz, 2012


– General format:

for ( initialization; loopContinuationTest; increment ) statement;

•If multiple statements needed, enclose in braces

•Control variable only exists in body of for structure – the variable’s scope

•If loopContinuationTest is initially false, body not executed

•All three expressions in a for header are optional.

•Omitting the loopContinuationCondition creates an infinite loop• for ( initialization; ; increment ) //an infinite loop statement;

•Omitting the initialization expression can be done if the control variable is initialized before the loop.•Omitting the increment expression can be done if the application calculates the increment with statements in the loop’s body or if no increment is needed.

Jozef Goetz, 2012


–General format:


• for ( initialization; ; increment ) //an infinite loop statement;

•If multiple statements needed, enclose in braces

•Control variable only exists in body of for structure – the variable’s scope

•If loopContinuationTest is initially false, body not executed


can usually be rewritten as an equivalent while structure:

initialization;while (loopContinuationTest )

{ statement

increment;}

Jozef Goetz, 2012

19

Good Programming Practice 6.2•In many cases, the prefix and postfix increment operators are both used to add 1 to a variable in a statement by itself.

•In these cases, the effect is exactly the same, except that the prefix increment operator has a slight performance advantage

•but if you choose the postfix incrementoperator, optimizing compilers will generate MSIL code that uses the more efficient form.

6.3 for Repetition Statement

Common Programming Error 6.5Placing a semicolon immediately to the right of the right parenthesis of a for header makes that for’s body an empty statement. This is normally a logic error.

Jozef Goetz, 2012

206.4 Examples Using the for Structure Varying control variable in for structure

Vary control variable from 1 to 100 in increments of 1 for ( int i = 1; i <= 100; i++ )

Vary control variable from 100 to 1 in decrements of –1 for ( int i = 100; i >= 1; i-- ) It counts downward

Vary control variable from 7 to 77 in steps of 7 for ( int i = 7; i <= 77; i += 7 )

The initialization, loop-continuation condition and increment portions of a for statement can contain arithmetic expressions. Let x = 2, y = 10for ( int j = x; j <= 4 * x * y; j += y / x )

equivalent tofor ( int j = 2; j <= 80; j += 5 )

Jozef Goetz, 2012

216.4 Examples Using the for Structure

Increment/Decrement When incrementing

In most cases < or <= is used - avoid off-by-one error

When decrementing In most cases > or >= is used - avoid off-by-one error

avoid off-by-one error Using an incorrect relational operator or an incorrect final

value of a loop counter in the condition of a while, for or do while statement can cause an off-by-one error or an infinite loop.

For zero-based counting test the loop if e.g. counter < 10 instead of counter <= 10 starting from counter = 0

Jozef Goetz, 2012

22Error-Prevention Tip 6.2 – 6.3

Although the value of the control variable can be changed in the body of a for loop, avoid doing so, because this practice can lead to

subtle errors.

Infinite loops occur when the loop-continuation condition in a repetition statement never becomes false. To prevent this situation in a counter-controlled loop,

ensure that the control variable is incremented (or decremented) during each iteration of the loop. In a sentinel-controlled loop, ensure that the sentinel

value is eventually input.

Jozef Goetz, 2012

23

1 // Fig. 6.5: Sum.cs

2 // Summing even integers with the for statement.

3 using System;

4

5 public class Sum

6 {


8 {

9 int total = 0; // initialize total

10

11 // total even integers from 2 through 20

12 for ( int number = 2; number <= 20; number += 2 )

13 total += number;

14

15 Console.WriteLine( "Sum is {0}", total ); // display results

16 } // end Main

17 } // end class Sum Sum is 110

Outline

Sum.cs

Example program:

Sum all the even integers from 2 to 20

Jozef Goetz, 2012


Massages boxes Icons

Exclamation Question Error Information

Message boxes Buttons

OK OKCancel YesNo AbortRetryIgnore YesNoCancel RetryCancel

Jozef Goetz, 2012


MessageBox Icons Icon Description MessageBoxIcon.Exclamation

Displays a dialog with an exclamation point. Typically used to caution the user against potential problems.

MessageBoxIcon.Information

Displays a dialog with an informational message to the user.

MessageBoxIcon.Question

Displays a dialog with a question mark. Typically used to ask the user a question.

MessageBoxIcon.Error

Displays a dialog with an x in a red circle. Helps alert user of errors or important messages.

Fig. Icons for message dialogs.

Jozef Goetz, 2012


MessageBox Buttons Description MessageBoxButton.OK Specifies that the dialog should include an OK button.

MessageBoxButton.OKCancel Specifies that the dialog should include OK and Cancel buttons. Warns the user about some condition and allows the user to either continue or cancel an operation.

MessageBoxButton.YesNo Specifies that the dialog should contain Yes and No buttons. Used to ask the user a question.

MessageBoxButton.YesNoCancel Specifies that the dialog should contain Yes, No and Cancel buttons. Typically used to ask the user a question but still allows the user to cancel the operation.

MessageBoxButton.RetryCancel Specifies that the dialog should contain Retry and Cancel buttons. Typically used to inform a user about a failed operation and allow the user to retry or cancel the operation.

MessageBoxButton.AbortRetryIgnore Specifies that the dialog should contain Abort, Retry and Ignore buttons. Typically used to inform the user that one of a series of operations has failed and allow the user to abort the series of operations, retry the failed operation or ignore the failed operation and continue.

Fig. Buttons for message dialogs.

Jozef Goetz, 2012


Compute compound interest Calculate the value each year of a $1000 deposit, yielding

5% annually Calculate the value for 10 years

Use

a = p (1 + r ) ⁿ – p - principal

– r - interest rate

– n - number of years

– a - amount on deposit after nth year

Example program Use a for loop to calculate interest

Jozef Goetz, 2012

286.4 Examples Using the for Structure static method accesss

ClassName.MethodName( arguments) “.” aceess operator

static methods do not need to be called on objects ( an instance of an object)

static method pow (class Math)

public static double Pow( double x, double y );

Math.pow( x, y )

Raises x to the yth power Takes two doubles, returns a double


Outline29

Interest.cs

1 // Fig. 5.8 ed1: Interest.cs2 // Calculating compound interest.3 4 using System;5 using System.Windows.Forms;6 7 class Interest8 {9 static void Main( string[] args )10 {11 decimal amount, principal = ( decimal ) 1000.00; 12 double rate = .05;13 string output;14 15 output = "Year\tAmount on deposit\n";16 17 for ( int year = 1; year <= 10; year++ )18 {19 amount = principal *20 ( decimal ) Math.Pow( 1.0 + rate, year );21 22 output += year + "\t" + 23 String.Format( "{0:C}", amount ) + "\n"; // {0} represents the argument being displayed24 }25 26 MessageBox.Show( output, "Compound Interest", 27 MessageBoxButtons.OK, MessageBoxIcon.Information );28 29 } // end method Main30 31 } // end class Interest

Creates a message box that displays the output with a title of “Compound Interest” has an OK button and an information icon

Loops through 10 times starting at 1 and ending at 10, adding 1 to the counter (year) each time

Insert a Tab

Formats amount to have a currency formatting ($0.00)

// a = p (1 + r ) ⁿ

Jozef Goetz, 2012

30

Jozef Goetz, 2012

31 1 // Fig. 6.6: Interest.cs

2 // Compound-interest calculations with for.

3 using System;

4

5 public class Interest

6 {


8 {

9 decimal amount; // amount on deposit at end of each year

10 decimal principal = 1000; // initial amount before interest

11 double rate = 0.05; // interest rate

12

13 // display headers

14 Console.WriteLine( "{0}{1,20}", "Year", "Amount on deposit" );

Outline

Different solution:

Interest.cs 15

16 // calculate amount on deposit for each of ten years

17 for ( int year = 1; year <= 10; year++ )

18 {

19 // calculate new amount for specified year

20 amount = principal *

21 ( ( decimal ) Math.Pow( 1.0 + rate, year ) );

22

23 // display the year and the amount 24 Console.WriteLine( "{0,4}{1,20:C}", year, amount );// a field width of // 20 chrs with right justification, -20 is left justification 25 } // end for

26 } // end Main

27 } // end class Interest

Year Amount on deposit 1 $1,050.00 2 $1,102.50 3 $1,157.63 4 $1,215.51 5 $1,276.28 6 $1,340.10 7 $1,407.10 8 $1,477.46 9 $1,551.33 10 $1,628.89

Jozef Goetz, 2012

326.4 Examples Using the for Statement (Cont.)

Formatting output Ex: {1, 20} Field width is after the comma Right justified To left justify, use the minus sign (-)

Jozef Goetz, 2012


Console.WriteLine( "{0,4}{1,20:C}", year, amount ); // a field width of // 20 with right justification, -20 is left justification “{1,20:F4}”

Format Specifier Description

C or c Formats the string as currency. Precedes the number with an appropriate currency symbol ($ in the US). Separates digits with an appropriate separator character (comma in the US) and sets the number of decimal places to two by default.

D or d Formats the string as a decimal. Displays number as an integer.

N or n Formats the string with commas and a default of two decimal places.

E or e Formats the number using scientific notation with a default of six decimal places.

F or f Formats the string with a fixed number of decimal places (two by default).

G or g General. Formats the number normally with decimal places or using scientific notation, depending on context. If a format item does not contain a format specifier, format G is assumed implicitly.

X or x Formats the string as hexadecimal.

Jozef Goetz, 2012


Beware rounding when performing monetary calculations using 4 bytes for Float (in .NET) or 8 bytes for Double to represent dollar amount

The imprecision of floating-points (Float or Double) can cause errors (assuming displaying Double with 2 decimal places):

Machine Display(rounded) Person14.234 -> 14.23 14.2318.673 -> 18.67 18.67

Total 32.907 -> 32.91 32.90

Use the data type Decimal (16 bytes) for monetary calculations

Do not use variables of type double (or float)

Jozef Goetz, 2012

356.5 do/while Repetition Structure The while loops vs. the do/while loops Format

do { statement }

while ( condition );

Good practice to put brackets in, even if not required

Using a do/while loop1. Action is performed2. Then the loop condition is tested3. Loop must be run though once

Using a while loop1. Condition is tested2. The action is performed3. Loop could be skipped altogether

true

false

action(s)

condition

Jozef Goetz, 2012

36 1 // Fig. 6.7: DoWhileTest.cs

2 // do...while repetition statement.

3 using System;

4

5 public class DoWhileTest

6 {


8 {

9 int counter = 1; // initialize counter

10

11 do

12 {

13 Console.Write( "{0} ", counter );

14 counter++;

15 } while ( counter <= 10 ); // end do...while

16

17 Console.WriteLine(); // outputs a newline

18 } // end Main

19 } // end class DoWhileTest 1 2 3 4 5 6 7 8 9 10

In loops, avoid calculations for which the result never changes —such calculations should typically be placed before the loop.

[Note: Optimizing compilers will typically place such calculations outside loops in the compiled code.]

Fig. 6.8 | do while repetition statement UML activity

diagram.

Jozef Goetz, 2012

37

Error-Prevention Tip Always include braces in a do...while statement, even if they are not necessary.

This helps eliminate ambiguity between while statements and do...while statements containing only one statement.

6.5 do...while Repetition Statement

Jozef Goetz, 2012

386.6 The switch Multiple-Selection Structure switch structure

Used for multiple selections Useful to test variable for different values

Different action taken

Format:switch ( variable){

case expr1:actions

case expr2:actions…

default: //optional but it is good programming practice to test it Actions // exceptional conditions

}

expr1,..exprn is 1. a variable or 2. a constant integral expression value which evaluates to (byte, sbyte,

short, ushort, int, uint, long, ulong or char type(e.g.‘A’) or 3. a constant string expression (is any expression composed of string

literals that always result on the same string) Series of case labels: case1: case2: actions an optional default case break; causes exit from structure

The switch multiple-selection statement performs different actions based on the value of an expression.

Each action is associated with the value of a constant integral expression or a constant string expression that the expression may assume.

Jozef Goetz, 2012

39

The expression following keyword switch is called the switch expression.

The application attempts to match the value of the switch expression with one of the case labels.

You are required to include a statement that terminates the case, such as a break, a return or a throw.

The break statement causes program control to proceed with the first statement after the switch.

If no match occurs, the statements after the default label execute.

Common Programming ErrorForgetting a break statement when one is needed in a switch is a compilation error.

6.6 The switch Multiple-Selection Structure

Jozef Goetz, 2012

406.6 switch Multiple-Selection Structure

break;

case: a case a action(s)true

false

.

.

.

break;

case b action(s) break;

false

false

case: z case z action(s) break;

default action(s)

true

true

case: b

Fig. 6.11 Flowcharting the switch multiple-selection structure.

The switch statement Constant expressions

String Integral

Cases Case ‘x’ :

– Use of constant variable cases

Empty cases The default case

The break – not included is a syntax error Exit the switch

statement

Jozef Goetz, 2012

41Fig. 6.11 | switch multiple-selection statement UML activity diagram with

break statements.

Common Programming ErrorForgetting a break statement when one is needed in a switch is a compilation error.

Good Programming Practice 6.4Although each case and the default label in a switch can occur in any order, place the default label last for clarity.


Outline42

SwitchTest.cs

1 // Fig. 6.10 ed1: SwitchTest.cs2 // Counting letter grades.3 4 using System;5 6 class SwitchTest7 {8 static void Main( string[] args )9 {10 char grade; // one grade11 int aCount = 0, // number of As12 bCount = 0, // number of Bs13 cCount = 0, // number of Cs14 dCount = 0, // number of Ds15 fCount = 0; // number of Fs16 17 for ( int i = 1; i <= 10; i++ )18 {19 Console.Write( "Enter a letter grade: " );20 grade = Char.Parse( Console.ReadLine() );21 22 switch ( grade )23 {24 case 'A': // grade is uppercase A25 case 'a': // or lowercase a26 ++aCount;27 break;28 29 case 'B': // grade is uppercase B30 case 'b': // or lowercase b31 ++bCount;32 break;33

Each of these variables acts as a counter so they are initialized to zero

The start of the switch statement. The grade variable is used as the data to be tested for each case.

Prompt the user for a grade and store it into the grade variable

case ‘A’ is empty so it is the same as case ‘a’

The break statement is used to exit the switch statement and not perform the rest of the operations

Both case ‘B’ and case ‘b’ add one to the bCount variable

Enter a letter grade: aEnter a letter grade: AEnter a letter grade: cEnter a letter grade: FEnter a letter grade: zIncorrect letter grade entered.Grade not added to totals.Enter a letter grade: DEnter a letter grade: dEnter a letter grade: BEnter a letter grade: aEnter a letter grade: C Totals for each letter grade are:A: 3B: 1C: 2D: 2F: 1


Outline43

SwitchTest.cs

34 case 'C': // grade is uppercase C35 case 'c': // or lowercase c36 ++cCount;37 break;38 39 case 'D': // grade is uppercase D40 case 'd': // or lowercase d41 ++dCount;42 break;43 44 case 'F': // grade is uppercase F45 case 'f': // or lowercase f46 ++fCount;47 break;48 49 default: // processes all other characters50 Console.WriteLine( 51 "Incorrect letter grade entered." +52 "\nGrade not added to totals." );53 break;54 55 } // end switch56 57 } // end for58 59 Console.WriteLine( 60 "\nTotals for each letter grade are:\nA: {0}" +61 "\nB: {1}\nC: {2}\nD: {3}\nF: {4}", aCount, bCount,62 cCount, dCount, fCount );63 64 } // end method Main65 66 } // end class SwitchTest

Both cases add 1 to cCount

If grade equals D or d add one to dCount

If non of the cases are equal to the value of grade then the default case is executed

Display the results

Enter a letter grade: aEnter a letter grade: AEnter a letter grade: cEnter a letter grade: FEnter a letter grade: zIncorrect letter grade entered.Grade not added to totals.Enter a letter grade: DEnter a letter grade: dEnter a letter grade: BEnter a letter grade: aEnter a letter grade: C Totals for each letter grade are:A: 3B: 1C: 2D: 2F: 1

Jozef Goetz, 2012

44 1 // Fig. 6.10: GradeBookTest.cs

2 // Create GradeBook object, input grades and display grade report.

3

4 public class GradeBookTest

5 {


7 {

8 // create GradeBook object myGradeBook and

9 // pass course name to constructor

10 GradeBook myGradeBook = new GradeBook(

11 "CS101 Introduction to C# Programming" );

12

13 myGradeBook.DisplayMessage(); // 1. display welcome message

14 myGradeBook.InputGrades(); // 2. read grades from user

15 myGradeBook.DisplayGradeReport(); // 3. display report based on grades

16 } // end Main

17 } // end class GradeBookTest

Outline

GradeBookTest.cs

Welcome to the grade book for CS101 Introduction to C# Programming! Enter the integer grades in the range 0-100. Type <Ctrl> z and press Enter to terminate input:

99 92 45 100 57 63 76 14 92 ^Z

Grade Report: Total of the 9 grades entered is 638 Class average is 70.89 Number of students who received each grade: A: 4 B: 0 C: 1 D: 1 F: 3

1.

2.

3.

Jozef Goetz, 2012

45 1 // Fig. 6.9: GradeBook.cs

2 // GradeBook class uses switch statement to count A, B, C, D and F grades.

3 using System;

4

5 public class GradeBook

6 {

7 // private string courseName; // name of course this GradeBook represents

8 private int total; // sum of grades

9 private int gradeCounter; // number of grades entered

10 private int aCount; // count of A grades

11 private int bCount; // count of B grades

12 private int cCount; // count of C grades

13 private int dCount; // count of D grades

14 private int fCount; // count of F grades 15 // automatic property CourseName

16 public string CourseName { get; set; }

// constructor initializes courseName;

17 // int instance variables are initialized to 0 by default

18 public GradeBook( string name )

19 {

20 CourseName = name; // initializes courseName

21 } // end constructor

Outline

GradeBook.cs

(1 of 5)

Keeping track of the sum of the grades and the number of grades entered, for averaging.

Counter variables for each grade category.

• Figure 6.9 contains an enhanced version of the GradeBook class.

Jozef Goetz, 2012

4622

23 // property that gets and sets the course name

24 /* public string CourseName

25 {

26 get

27 {

28 return courseName;

29 } // end get

30 set

31 {

32 courseName = value;

33 } // end set

34 } // end property CourseName

35 */

36 // display a welcome message to the GradeBook user

37 public void DisplayMessage()

38 {

39 // CourseName gets the name of the course

40 Console.WriteLine( "Welcome to the grade book for\n{0}!\n",

41 CourseName );

42 } // end method DisplayMessage

Outline

GradeBook.cs

(2 of 5)

Welcome to the grade book for CS101 Introduction to C# Programming! Enter the integer grades in the range 0-100. Type <Ctrl> z and press Enter to terminate input: 99 92 45 100 57 63 76 14 92 ^Z


Jozef Goetz, 2012

47

Outline

GradeBook.cs

(3 of 5)

43

44 // input arbitrary number of grades from user

45 public void InputGrades()

46 {

47 int grade; // grade entered by user

48 string input; // text entered by the user

49

50 Console.WriteLine( "{0}\n{1}",

51 "Enter the integer grades in the range 0-100.",

52 "Type <Ctrl> z and press Enter to terminate input:" );

53

54 input = Console.ReadLine(); // read user input

55

56 // loop until user enters (null) the end-of-file indicator ( <Ctrl> z)

57 while ( input != null ) // compare a string reference with a null

58 {

59 grade = Convert.ToInt32( input ); // read grade off user input

60 total += grade; // add grade to total

61 gradeCounter++; // increment number of grades

62

63 // call method to increment appropriate counter

64 IncrementLetterGradeCounter( grade );

65

66 input = Console.ReadLine(); // read user input

67 } // end while

68 } // end method InputGrades



Jozef Goetz, 2012

48

Outline

GradeBook.cs

(4 of 5)

69

70 // add 1 to appropriate counter for specified grade

71 private void IncrementLetterGradeCounter( int grade ) //helper

72 {

73 // determine which grade was entered

74 switch ( grade / 10 )

75 {

76 case 9: // grade was in the 90s

77 case 10: // grade was 100

78 aCount++; // increment aCount

79 break; // necessary to exit switch

80 case 8: // grade was between 80 and 89

81 bCount++; // increment bCount

82 break; // exit switch


84 cCount++; // increment cCount



87 dCount++; // increment dCount


89 default: // grade was less than 60

90 fCount++; // increment fCount


92 } // end switch

93 } // end method IncrementLetterGradeCounter

• A switch statement determines whether each grade is an A, B, C, D or F.

Jozef Goetz, 2012

49

Outline

GradeBook.cs

(5 of 5)

94

95 // display a report based on the grades entered by the user

96 public void DisplayGradeReport()

97 {

98 Console.WriteLine( "\nGrade Report:" );

99

100 // if user entered at least one grade...

101 if ( gradeCounter != 0 )

102 {

103 // calculate average of all grades entered

104 double average = ( double ) total / gradeCounter;

105

106 // output summary of results

107 Console.WriteLine( "Total of the {0} grades entered is {1}",

108 gradeCounter, total );

109 Console.WriteLine( "Class average is {0:F2}", average );

110 Console.WriteLine( "{0}A: {1}\nB: {2}\nC: {3}\nD: {4}\nF: {5}",

111 "Number of students who received each grade:\n",

112 aCount, // display number of A grades

113 bCount, // display number of B grades

114 cCount, // display number of C grades

115 dCount, // display number of D grades

116 fCount ); // display number of F grades

117 } // end if

118 else // no grades were entered, so output appropriate message

119 Console.WriteLine( "No grades were entered" );

120 } // end method DisplayGradeReport

121 } // end class GradeBook



Jozef Goetz, 2012

50 1 // Fig. 6.10: GradeBookTest.cs

2 // Create GradeBook object, input grades and display grade report.

3

4 public class GradeBookTest

5 {


7 {

8 // create GradeBook object myGradeBook and

9 // pass course name to constructor

10 GradeBook myGradeBook = new GradeBook(

11 "CS101 Introduction to C# Programming" );

12

13 myGradeBook.DisplayMessage(); // display welcome message

14 myGradeBook.InputGrades(); // read grades from user

15 myGradeBook.DisplayGradeReport(); // display report based on grades

16 } // end Main

17 } // end class GradeBookTest

Outline

GradeBookTest.cs

Welcome to the grade book for CS101 Introduction to C# Programming! Enter the integer grades in the range 0-100. Type <Ctrl> z and press Enter to terminate input:

99 92 45 100 57 63 76 14 92 ^Z


Jozef Goetz, 2012

516.7 Statements break and continue Alter the flow of control break statement

Causes immediate exit from control structure Used in while, for, do/while or switch statements

Program continues with the first statement after the structure Common uses of the break statement

Escape early from a loop Skip the remainder of a switch structure

continue statement

Skips the remaining statements in body of while, for or do/while

Proceeds with the next iteration of the loop while and do/while

Loop-continuation test is evaluated immediately after continue for structure

Increment expression is executed, then the loop-continuation test is evaluated

Jozef Goetz, 2012

526.7 Statements break and continue

Used to alter the flow of control

The break statement Used to exit a loop early

The continue statement Used to skip the rest of the statements and begin

the loop at the first statement in the loop Programs can be completed without their usage

Jozef Goetz, 2012

53 1 // Fig. 6.12: BreakTest.cs

2 // break statement exiting a for statement.

3 using System;

4

5 public class BreakTest

6 {


8 {

9 int count; // control variable also used after loop terminates

10

11 for ( count = 1; count <= 10; count++ ) // loop 10 times

12 {

13 if ( count == 5 ) // if count is 5,

14 break; // terminate loop

15

16 Console.Write( "{0} ", count );

17 } // end for

18

19 Console.WriteLine( "\nBroke out of loop at count = {0}", count );

20 } // end Main

21 } // end class BreakTest 1 2 3 4 Broke out of loop at count = 5

Outline

BreakTest.cs

Loop 10 times

Exit for statement (break) when count equals 5


Outline54

BreakTest.cs

1 // Fig. 6.12: BreakTest.cs with a MessageBox2 // Using the break statement in a for structure.3 4 using System;5 using System.Windows.Forms;6 7 class BreakTest8 {9 static void Main( string[] args ) 10 {11 string output = "";12 int count;13 14 for ( count = 1; count <= 10; count++ )15 {16 if ( count == 5 )17 break; // skip remaining code in loop 18 // if count == 519 20 output += count + " ";21 22 } // end for loop23 24 output += "\nBroke out of loop at count = " + count;25 // Display the last value that the counter was at before it broke26 MessageBox.Show( output, "Demonstrating the break statement",27 MessageBoxButtons.OK, MessageBoxIcon.Information );28 29 } // end method Main30 31 } // end class BreakTest

Displays a message box the displays the output, has a title of “demonstrating the break statement,” uses an OK button, and displays an information icon

A loop that starts at one, goes to ten, and increments by one

If count = 5 then break out of the loop

Jozef Goetz, 2012

55 1 // Fig. 6.13: ContinueTest.cs

2 // continue statement terminating an iteration of a for statement.

3 using System;

4

5 public class ContinueTest

6 {


8 {

9 for ( int count = 1; count <= 10; count++ ) // loop 10 times

10 {

11 if ( count == 5 ) // if count is 5,

12 continue; // skip remaining code in loop

13

14 Console.Write( "{0} ", count );

15 } // end for

16

17 Console.WriteLine( "\nUsed continue to skip printing 5" );

18 } // end Main

19 } // end class ContinueTest 1 2 3 4 6 7 8 9 10 Used continue to skip printing 5

Outline

ContinueTest.csLoop 10 times

Skip line 14 and proceed to line 9 when count equals 5


Outline56

ContinueTest.cs

1 // Fig. 6.13: ContinueTest.cs with a MessageBox2 // Using the continue statement in a for structure.3 4 using System;5 using System.Windows.Forms;6 7 class ContinueTest8 {9 static void Main( string[] args ) 10 {11 string output = "";12 13 for ( int count = 1; count <= 10; count++ )14 {15 if ( count == 5 )16 continue; // skip remaining code in loop17 // only if count == 518 19 output += count + " ";20 }21 22 output += "\nUsed continue to skip printing 5";23 24 MessageBox.Show( output, "Using the continue statement",25 MessageBoxButtons.OK, MessageBoxIcon.Information );26 27 } // end method Main28 29 } // end class ContinueTest

A loop that starts at 1, goes to 10, and increments by 1

If count = 5 then continue looping causing the program to skip the rest of the loop

Create a message box that displays the output, has the title “using the continue statement,” uses an button, and displays an information icon.

Jozef Goetz, 2012

57Software Engineering Observation 6.2

Some programmers feel that break and continue statements violate structured programming.

Since the same effects are achievable with structured programming techniques, these programmers prefer not to use break or continue statements.

Jozef Goetz, 2012

58TIPSPerformance Tips

The break and continue statements, when used properly, perform faster than the corresponding structured techniques.

Software Engineering Observation There is a tension between achieving quality software

engineering and achieving the best performing software. Often, one of these goals is achieved at the expense of the other.

For all but the most performance-intensive situations, apply the

following rule of thumb:

First, make your code simple and correct; then make it fast and small, but only if necessary.

Jozef Goetz, 2012

596.8 Logical and Conditional Operators

Used to add multiple conditions to a statement Operators

Allows for forming more complex conditions Combines simple conditions

Logical AND (&), Conditional AND (&&) Returns true if both conditions are true

Logical OR (|) , Conditional OR (||) Returns true if either of its conditions are true

Logical exclusive OR or XOR (^)

Returns false when the two conditionals are the same Logical NOT (!)

Reverses the truth/falsity of its condition Unary operator, has one operand Can be avoided if desired by using other conditional operators

Jozef Goetz, 2012

606.8 Logical Operators

Logical Operators & (Logical exclusive OR or XOR )

true if exactly one condition true

| (inclusive OR) = Boolean logical OR All logical operators & and | always evaluates both

expressions (no short-circuit evaluation)– Useful if right operand has a needed side effect

birthday == true | ++age >= 65– Avoid expressions with side effects – more trouble than

they are worth.

Short circuit evaluation is applied only to Conditional AND (&&) and OR (||):

Evaluate left operand, decide whether to evaluate right operand If left operand of && is false, will not evaluate right operand

Boolean logical AND (&) and OR(|) work identical to conditional AND (&&) and logical OR (||)

Jozef Goetz, 2012

616.8 Logical Operators

Examples

Expression Result

true && false falsetrue || false true

!false truetrue ^ true false

if ( ( gender == 1 ) && ( age >= 65 ) ) ++seniorFemales;

seniorFemales updated if both conditions true

Jozef Goetz, 2012


expression1 expression2 expression1 && expression2

false false false false true false true false false true true true Fig. 6.14 Truth table for the && (conditional AND) operator.

expression1 expression2 expression1 || expression2

false false false false true true true false true true true true Fig. 6.15 Truth table for the || (conditional OR) operator.

if ( ( semesterAverage >= 90 ) || ( finalExam >= 90 ) ) Console.WriteLine ( "Student grade is A" );

Jozef Goetz, 2012


expression1 expression2 expression1 ^ expression2

false false false false true true true false true true true false Fig. 6.16 Truth table for the logical exclusive OR (^) operator.

expression !expression false true True false Fig. 6.17 Truth table for operator! (logical NOT).

if ( grade != sentinelValue ) Console.WriteLine( "The next grade is {0}", grade );


Outline64

LogicalOperators.cs

1 // Fig. 6.18: LogicalOperators.cs2 // Demonstrating the logical operators.3 using System;4 5 class LogicalOperators6 {7 // main entry point for application8 static void Main( string[] args )9 {10 // testing the conditional AND operator (&&)11 Console.WriteLine( "Conditional AND (&&)" +12 "\nfalse && false: " + ( false && false ) +13 "\nfalse && true: " + ( false && true ) +14 "\ntrue && false: " + ( true && false ) +15 "\ntrue && true: " + ( true && true ) );16 17 // testing the conditional OR operator (||)18 Console.WriteLine( "\n\nConditional OR (||)" +19 "\nfalse || false: " + ( false || false ) +20 "\nfalse || true: " + ( false || true ) +21 "\ntrue || false: " + ( true || false ) +22 "\ntrue || true: " + ( true || true ) );23 24 // testing the logical AND operator (&)25 Console.WriteLine( "\n\nLogical AND (&)" +26 "\nfalse & false: " + ( false & false ) +27 "\nfalse & true: " + ( false & true ) +28 "\ntrue & false: " + ( true & false ) +29 "\ntrue & true: " + ( true & true ) );30

Only true if both inputs are true

Only false if both inputs are false

The result is only true if both are true

Outputs a truth table for the conditional AND operator (&&)

Outputs a truth table for the conditional OR operator (||)

Outputs a truth table for the logical AND operator (&)

Conditional AND (&&)false && false: Falsefalse && true: Falsetrue && false: Falsetrue && true: True

Conditional OR (||)false || false: Falsefalse || true: Truetrue || false: Truetrue || true: True

Logical AND (&)

false & false: False

false & true: False

true & false: False

true & true: True


Outline65

LogicalOperators.cs

Program Output

Notice in ed4: lines 38-44 have different output format than others

31 // testing the logical OR operator (|)32 Console.WriteLine( "\n\nLogical OR (|)" +33 "\nfalse | false: " + ( false | false ) +34 "\nfalse | true: " + ( false | true ) +35 "\ntrue | false: " + ( true | false ) +36 "\ntrue | true: " + ( true | true ) );37 // create truth table for ^ (boolean logical exclusive OR) operator 39 Console.WriteLine( "{0}\n{1}: {2}\n{3}: {4}\n{5}: {6}\n{7}: {8}\n",40 "Boolean logical exclusive OR (^)",41 "false ^ false", ( false ^ false ),42 "false ^ true", ( false ^ true ),43 "true ^ false", ( true ^ false ),44 "true ^ true", ( true ^ true ) );45 // testing the logical NOT operator (!)46 Console.WriteLine( "\n\nLogical NOT (!)" +47 "\n!false: " + ( !false ) +48 "\n!true: " + ( !true ) );49 }50 } Returns the opposite as the input

Returns false when the two conditionals are the same

If one is true the result is true

Outputs a truth table for the logical OR operator (||)

Outputs a truth table for the logical exclusive OR operator (||)

Outputs a truth table for the logical NOT operator (!)

Logical OR (|)

false | false: False

false | true: True

true | false: True

true | true: True

Logical exclusive OR (^)

false ^ false: False

false ^ true: True

true ^ false: True

true ^ true: False

Logical NOT (!)

!false: True

!true: False

Jozef Goetz, 2012


Operators Associativity Type

. new ++(postfix) --(postfix) left to right highest precedence

++ -- + - ! (type) right to left unary prefix

* / % left to right multiplicative

+ - left to right additive

< <= > >= left to right relational

== != left to right equality

& left to right boolean logical AND

^ left to right boolean logical exclusive OR

| left to right boolean logical inclusive OR

&& left to right conditional AND

|| left to right conditional OR

?: right to left conditional

= += -= *= /= %= right to left assignment

Fig. 6.19 | Precedence/associativity of the operators discussed

so far.

Jozef Goetz, 2012

676.9 Structured Programming Summary

Produces programs that are: easy to understand, test, debug and modify them and even prove correct in a mathematical sense.

Control Structures Only one entrance Only one exit Building blocks to programming Allow nesting Makes code neater and easier to follow No overlapping structures

The goto keyword

Jozef Goetz, 2012


3 forms of control necessary Many ways to implement these controls Sequential (only 1 way)

Straight forward programming

Selection (3 ways) if selection (one choice) if/else selection (two choices) switch statement (multiple choices)

Repetition (4 ways) while structure do/while structure for structure foreach structure (chapter 7)

Jozef Goetz, 2012


Connecting control structures: the exit point of one control structure connects to the entry point the next control structure (control-structure stacking).

Any these control structures can be combined in only 2 ways: control-structure stacking and nesting.

Jozef Goetz, 2012

70Fig. 6.20 | C#’s single-entry/single-exit sequence, selection and repetition

statements.

Jozef Goetz, 2012


Rules for Forming Structured Programs 1) Begin with the “simplest flowchart” (Fig. 6.22). 2) The Stacking Rule. Any rectangle (action) can be replaced by two

rectangles (actions) in sequence. 3) The Nesting Rule. Any rectangle (action) can be replaced by any control

structure (sequence, if, if/else, switch, while, do/while, for or foreach, as we will see in Chapter 8).

4) Rules 2 and 3 may be applied as often as you like and in any order. Fig. 6.21 Rules for forming structured programs.

Jozef Goetz, 2012

72Fig. 6.22 | Simplest activity diagram.

Jozef Goetz, 2012

73Fig. 6.23 | Repeatedly applying the stacking rule (Rule 2) of Fig. 6.21 to the simplest activity diagram.

Jozef Goetz, 2012

74Fig. 6.24 | Repeatedly applying the nesting rule (Rule 3)

of Fig. 6.21 to the simplest activity diagram.

Jozef Goetz, 2012

75Fig. 6.25 | “Unstructured” activity diagram.

Jozef Goetz, 2012


Fig. 6.27 Stacked, nested and overlapped building blocks.

Stacked building blocks

Overlapping building blocks (illegal in structured programs)

Nested building blocks

Combination of control structures:

1. Stacking

Placing one after another

2. Nesting

Inserting of one structure into another

Jozef Goetz, 2012

77Structured Programming Summary

All programs can be written in terms of 3 control structures Sequence, Selection and Repetition (Bohm and Jacopini)

All structured programs can be broken down into 3 parts Sequence - trivial Selection - if, if/else, or switch

Can be rewritten as an if statement

Repetition - while, do/while, or for Can be rewritten as a while statement

Structured programs can be reduced by applying rules 1-4 in reverse to the simplest flowchart.

Jozef Goetz, 2012

Jozef Goetz, 2012

79 Output sum s for x = 0, 0.1, 0.2, …0.9, 1 in the table format

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