2006 pearson education, inc. all rights reserved. 1 6 6 control statements: part 2
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2006 Pearson Education, Inc. All rights reserved.
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
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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
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OBJECTIVESIn this chapter you will learn: The essentials of counter-controlled
repetition. To use the for and do...while repetition
statements to execute statements in an application repeatedly.
To understand multiple selection using the switch selection statement.
To use the break and continue program control statements to alter the flow of control.
To use the logical operators to form complex conditional expressions in control statements.
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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
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6.1 Introduction
• Continue structured-programming discussion– Introduce C#’s remaining control structures
• for, do…while, switch
– Introduce the break and continue statements
– Introduce the logical operators
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Common 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.
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Error-Prevention Tip 6.1
Control counting loops with integers.
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6.2 Essentials of Counter-Controlled Repetition
• Counter-controlled repetition requires:– Control variable (loop counter)
– Initial value of the control variable
– Increment/decrement of control variable through each loop
– Loop-continuation condition that tests for the final value of the control variable
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1 // Fig. 6.1: WhileCounter.cs
2 // Counter-controlled repetition with the while repetition statement.
3 using System;
4
5 public class WhileCounter
6 {
7 public static void Main( string[] args )
8 {
9 int counter = 1; // declare and initialize control variable
10
11 while ( counter <= 10 ) // loop-continuation condition
12 {
13 Console.Write( "{0} ", counter );
14 counter++; // increment control variable
15 } // end while
16
17 Console.WriteLine(); // output a newline
18 } // end Main
19 } // end class WhileCounter 1 2 3 4 5 6 7 8 9 10
Outline
WhileCounter.cs
Control-variable name is counter
Control-variable initial value is 1
Condition tests for counter’s final value
Increment for counter
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Good Programming Practice 6.1
Place blank lines above and below repetition and selection control statements, and indent the statement bodies to enhance readability.
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Software Engineering Observation 6.1
“Keep it simple” is good advice for most of the code you will write.
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6.3 for Repetition Statement
• Handles counter-controlled-repetition details
• Format:for ( initialization; loopContinuationCondition; increment )
statement;
– If the counter is initialize in the For…Next header, then that variable has a scope of that loop.
• Can usually be rewritten as:initialization;while ( loopContinuationCondition )
{ statement; increment;}
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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 <= 10; 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 6 7 8 9 10
Outline
ForCounter.cs
Control-variable name is counter
Control-variable initial value is 1
Condition tests for counter’s final value
Increment for counter
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Common Programming Error 6.2
Using an incorrect relational operator or an incorrect final value of a loop counter in the loop-continuation condition of a repetition statement causes an off-by-one error.
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Good Programming Practice 6.2
Using the final value in the condition of a while or for statement with the <= relational operator helps avoid off-by-one errors. For a loop that prints the values 1 to 10, the loop-continuation condition should be counter <= 10, rather than counter < 10 (which causes an off-by-one error) or counter < 11 (which is correct). Many programmers prefer so-called zero-based counting, in which to count 10 times, counter would be initialized to zero and the loop-continuation test would be counter < 10.
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Common Programming Error 6.3
Using commas instead of the two required semicolons in a for header is a syntax error.
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Common Programming Error 6.4
When a for statement’s control variable is declared in the initialization section of the for’s header, using the control variable after the for’s body is a compilation error.
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Performance Tip 6.1
There is a slight performance advantage to using the prefix increment operator, but if you choose the postfix increment operator because it seems more natural (as in a for header), optimizing compilers will generate MSIL code that uses the more efficient form anyway.
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Good Programming Practice 6.3
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. Given that the compiler typically optimizes your code to help you get the best performance, use the idiom (prefix or postfix) with which you feel most comfortable in these situations.
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Common Programming Error 6.5
Placing 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.
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Error-Prevention Tip 6.2
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.
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Error-Prevention Tip 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.
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Fig. 6.4 | UML activity diagram for the for statement in Fig. 6.2.
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6.4 Examples Using the for Statement
• Varying control variable in for headers– 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 increments of –1• for ( int i = 100; i >= 1; i-- )
– Vary control variable from 7 to 77 in increments of 7• for ( int i = 7; i <= 77; i += 7 )
– Vary control variable from 20 to 2 in decrements of -2• for ( int i = 20; i >= 2; i -= 2 )
– Vary control variable over the sequence: 2, 5, 8, 11, 14, 17, 20• for ( int i = 2; i <= 20; i += 3 )
– Vary control variable over the sequence: 99, 88, 77, 66, 55, 44, 33, 22, 11, 0• for ( int i = 99; i >= 0; i -= 11 )
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Common Programming Error 6.6
Not using the proper relational operator in the loop-continuation condition of a loop that counts downward (e.g., using i <= 1 instead of i >= 1 in a loop counting down to 1) is a logic error.
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1 // Fig. 6.5: Sum.cs
2 // Summing integers with the for statement.
3 using System;
4
5 public class Sum
6 {
7 public static void Main( string[] args )
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
increment number by 2 each iteration
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6.4 Examples Using the for Statement (Cont.)
• Initialization and increment expression can be comma-separated lists of expressions
– E.g., lines 12-13 of Fig. 6.5 can be rewritten as
for ( int number = 2; number <= 20; total += number, number += 2 )
; // empty statement
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Good Programming Practice 6.4
Limit the size of control statement headers to a single line if possible.
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Good Programming Practice 6.5
Place only expressions involving the control variables in the initialization and increment sections of a for statement. Manipulations of other 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 increment or decrement statements).
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1 // Fig. 6.6: Interest.cs
2 // Compound-interest calculations with for.
3 using System;
4
5 public class Interest
6 {
7 public static void Main( string[] args )
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
Interest.cs
(1 of 2)
Second string is right justified and displayed with a field width of 20
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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 );
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
Outline
Interest.cs
(2 of 2)
Calculate amount with for statement
amount is displayed right justified in currency format
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6.4 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 (-)
•static method– ClassName.methodName( arguments)
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Good Programming Practice 6.6
Do not use variables of type double (or float) to perform precise monetary calculations; use type decimal instead. The imprecision of floating-point numbers can cause errors that will result in incorrect monetary values.
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Performance Tip 6.2
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.]
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6.5 do…while Repetition Statement
•do…while structure– Similar to while structure
– Tests loop-continuation after performing body of loop• i.e., loop body always executes at least once
• Format:
do
statement;
while ( condition );
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1 // Fig. 6.7: DoWhileTest.cs
2 // do...while repetition statement.
3 using System;
4
5 public class DoWhileTest
6 {
7 public static void Main( string[] args )
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
Outline
DoWhileTest.cs
Declares and initializes control variable counter
Variable counter’s value is displayed before testing counter’s final value
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Fig. 6.8 | do while repetition statement UML activity diagram.
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Error-Prevention Tip 6.4
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.
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6.6 switch Multiple-Selection Statement
•switch statement– Used for multiple selections
• Each case must have a break – Exception: case body is empty and it falls through to
another case
• Goes to default if none of the cases matches– Optional
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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
16 // 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)
Variables to be incremented determined by the switch
statement
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22
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)
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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 the end-of-file indicator (<Ctrl> z)
57 while ( input != 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
Display prompt
Loop condition: if there is more data input
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Outline
GradeBook.cs
(4 of 5)
69
70 // add 1 to appropriate counter for specified grade
71 private void IncrementLetterGradeCounter( int grade )
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
83 case 7: // grade was between 70 and 79
84 cCount++; // increment cCount
85 break; // exit switch
86 case 6: // grade was between 60 and 69
87 dCount++; // increment dCount
88 break; // exit switch
89 default: // grade was less than 60
90 fCount++; // increment fCount
91 break; // exit switch
92 } // end switch
93 } // end method IncrementLetterGradeCounter
switch statement determines which case label to execute,
depending on controlling expression
(grade / 10 ) is the controlling expression
default case for grade less than 60
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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
Prints out results
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Common Programming Error 6.7
Forgetting a break statement when one is needed in a switch is a syntax error.
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1 // Fig. 6.10: GradeBookTest.cs
2 // Create GradeBook object, input grades and display grade report.
3
4 public class GradeBookTest
5 {
6 public static void Main( string[] args )
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
(1 of 2)
Call GradeBook public methods to count grades
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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
Outline
GradeBookTest.cs
(2 of 2)
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Software Engineering Observation 6.2
Provide a default label in switch statements. Cases not explicitly tested in a switch that lacks a default label are ignored. Including a default label focuses you on the need to process exceptional conditions.
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Good Programming Practice 6.7
Although each case and the default label in a switch can occur in any order, place the default label last for clarity.
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6.6 switch Multiple-Selection Statement (Cont.)
• Utility / helper methods– private methods to support other methods
• Expression in each case– Constant integral expression
• Combination of integer constants that evaluates to a constant integer value
– Character constant• E.g., ‘A’, ‘7’ or ‘$’
– Constant variable
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Fig. 6.11 | switch multiple-selection statement UML activity diagram with break statements.
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6.7 break and continue Statements
•break/continue– Alter flow of control
•break statement – Causes immediate exit from control structure
• Used in while, for, do…while, switch, or foreach statements
•continue statement – Skips remaining statements in loop body
– Proceeds to next iteration• Used in while, for, do…while or foreach statements
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1 // Fig. 6.12: BreakTest.cs
2 // break statement exiting a for statement.
3 using System;
4
5 public class BreakTest
6 {
7 public static void Main( string[] args )
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.csLoop 10 times
Exit for statement (break) when count equals 5
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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 {
7 public static void Main( string[] args )
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
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Software Engineering Observation 6.3
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.
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Software Engineering Observation 6.4
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.
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6.8 Logical Operators
• Logical operators– Allows for forming more complex conditions
– Combines simple conditions
• C# logical operators– && (conditional AND)
– || (conditional OR)
– & (boolean logical AND)
– | (boolean logical inclusive OR)
– ^ (boolean logical exclusive OR)
– ! (logical NOT)
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6.8 Logical Operators (Cont.)
• Conditional AND (&&) Operator– Consider the following if statement
if ( gender == FEMALE && age >= 65 )
seniorFemales++;
– Combined condition is true • if and only if both simple conditions are true
– Combined condition is false • if either or both of the simple conditions are false
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Fig. 6.14 | && (conditional AND) operator truth table.
expression1 expression2 expression1 && expression2
false false false
false true false
true false false
true true true
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6.8 Logical Operators (Cont.)
• Conditional OR (||) Operator– Consider the following if statement
if ( ( semesterAverage >= 90 ) || ( finalExam >= 90 )
Console.WriteLine( “Student grade is A” );
– Combined condition is true • if either or both of the simple condition are true
– Combined condition is false • if both of the simple conditions are false
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Fig. 6.15 | || (conditional OR) operator truth table.
expression1 expression2 expression1 || expression2
false false false
false true true
true false true
true true true
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6.8 Logical Operators (Cont.)
• Short-Circuit Evaluation of Complex Conditions– Parts of an expression containing && or || operators are
evaluated only until it is known whether the condition is true or false
– E.g., ( gender == FEMALE ) && ( age >= 65 )• Stops immediately if gender is not equal to FEMALE
65
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Common Programming Error 6.8
In expressions using operator &&, a condition—which we refer to as the dependent condition—may require another condition to be true for the evaluation of the dependent condition to be meaningful. In this case, the dependent condition should be placed after the other condition, or an error might occur. For example, in the expression ( i != 0 ) && ( 10 / i == 2 ), the second condition must appear after the first condition, or a divide-by-zero error might occur.
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6.8 Logical Operators (Cont.)
• Boolean Logical AND (&) Operator– Works identically to &&
– Except & always evaluate both operands
• Boolean Logical OR (|) Operator – Works identically to ||
– Except | always evaluate both operands
67
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Error-Prevention Tip 6.5
For clarity, avoid expressions with side effects in conditions. The side effects may look clever, but they can make it harder to understand code and can lead to subtle logic errors.
68
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6.8 Logical Operators (Cont.)
• Boolean Logical Exclusive OR (^)– One of its operands is true and the other is false
• Evaluates to true
– Both operands are true or both are false• Evaluates to false
• Logical Negation (!) Operator– Unary operator
– Opposite of the boolean value
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Fig. 6.16 | ^ (boolean logical exclusive OR) operator truth table.
expression1 expression2 expression1 ^ expression2
false false false
false true true
true false true
true true false
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Fig. 6.17 | ! (logical negation) operator truth table.
expression !expression
false true
true false
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1 // Fig. 6.18: LogicalOperators.cs
2 // Logical operators.
3 using System;
4
5 public class LogicalOperators
6 {
7 public static void Main( string[] args )
8 {
9 // create truth table for && (conditional AND) operator
10 Console.WriteLine( "{0}\n{1}: {2}\n{3}: {4}\n{5}: {6}\n{7}: {8}\n",
11 "Conditional AND (&&)", "false && false", ( false && false ),
12 "false && true", ( false && true ),
13 "true && false", ( true && false ),
14 "true && true", ( true && true ) );
15
16 // create truth table for || (conditional OR) operator
17 Console.WriteLine( "{0}\n{1}: {2}\n{3}: {4}\n{5}: {6}\n{7}: {8}\n",
18 "Conditional OR (||)", "false || false", ( false || false ),
19 "false || true", ( false || true ),
20 "true || false", ( true || false ),
21 "true || true", ( true || true ) );
22
23 // create truth table for & (boolean logical AND) operator
24 Console.WriteLine( "{0}\n{1}: {2}\n{3}: {4}\n{5}: {6}\n{7}: {8}\n",
25 "Boolean logical AND (&)", "false & false", ( false & false ),
26 "false & true", ( false & true ),
27 "true & false", ( true & false ),
28 "true & true", ( true & true ) );
Outline
LogicalOperators.cs
(1 of 3)
Conditional AND truth operator
Boolean logical AND operator
Conditional OR truth operator
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29
30 // create truth table for | (boolean logical inclusive OR) operator
31 Console.WriteLine( "{0}\n{1}: {2}\n{3}: {4}\n{5}: {6}\n{7}: {8}\n",
32 "Boolean logical inclusive OR (|)",
33 "false | false", ( false | false ),
34 "false | true", ( false | true ),
35 "true | false", ( true | false ),
36 "true | true", ( true | true ) );
37
38 // 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
46 // create truth table for ! (logical negation) operator
47 Console.WriteLine( "{0}\n{1}: {2}\n{3}: {4}",
48 "Logical negation (!)", "!false", ( !false ),
49 "!true", ( !true ) );
50 } // end Main
51 } // end class LogicalOperators
Outline
LogicalOperators.cs
(2 of 3)
Boolean logical inclusive OR operator
Boolean logical exclusive OR operator
Logical negation operator
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Conditional AND (&&) false && false: False false && true: False true && false: False true && true: True Conditional OR (||) false || false: False false || true: True true || false: True true || true: True Boolean logical AND (&) false & false: False false & true: False true & false: False true & true: True Boolean logical inclusive OR (|) false | false: False false | true: True true | false: True true | true: True Boolean logical exclusive OR (^) false ^ false: False false ^ true: True true ^ false: True true ^ true: False Logical negation (!) !false: True !true: False
Outline
LogicalOperators.cs
(3 of 3)
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Fig. 6.19 | Precedence/associativity of the operators discussed so far.
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
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6.9 Structured Programming Summary
• Sequence structure– “built-in” to C#
• Selection structure– if, if…else and switch
• Repetition structure– while, do…while, for, and foreach
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Fig. 6.20 | C#’s single-entry/single-exit sequence, selection and repetition statements.
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Fig. 6.21 | Rules for forming structured applications.
Rules for Forming Structured Applications
1 Begin with the simplest activity diagram (Fig. 6.22).
2 Any action state can be replaced by two action states in sequence.
3 Any action state can be replaced by any control statement (sequence of action states, if, if else, switch, while, do while, for or foreach, which we will see in Chapter 8).
4 Rules 2 and 3 can be applied as often as necessary in any order.
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Fig. 6.23 | Repeatedly applying the stacking rule (Rule 2) of Fig. 6.21 to the simplest activity diagram.
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Fig. 6.24 | Repeatedly applying the nesting rule (Rule 3) of Fig. 6.21 to the simplest activity diagram.
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6.10 (Optional) Software Engineering Case Study: Identifying Objects’ State and Activities in the ATM System• State Machine Diagrams
– Commonly called state diagram
– Model several states of an object
– Show under what circumstances the object changes state
– Focus on system behavior
– UML representation• State
- Rounded rectangle
• Initial state
- Solid circle
• Transitions
- Arrows with stick arrowheads
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Software Engineering Observation 6.5
Software designers do not generally create state machine diagrams showing every possible state and state transition for all attributes—there are simply too many of them. State machine diagrams typically show only the most important or complex states and state transitions.
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Fig. 6.26 | State machine diagram for some of the states of the ATM object.
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6.10 (Optional) Software Engineering Case Study: Identifying Objects’ State and Activities in the ATM System (Cont.)• Activity Diagrams
– Focus on system behavior
– Model an object’s workflow during program execution
– Model the actions the object will perform and in what order
– UML representation• Action state ( rectangle with its left and right sides replaced
by arcs curving outwards)
• Action order ( arrow with a stick arrowhead)
• Initial state (solid circle)
• Final state (solid circle enclosed in an open circle)
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Fig. 6.27 | Activity diagram for a BalanceInquiry transaction.
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Fig. 6.28 | Activity diagram for a Withdrawal transaction.