Download ppt - 2001 Prentice Hall, Inc. All rights reserved. 1 Chapter 17 - WMLScript: Control Structures I Outline 17.1 Introduction 17.2 Algorithms 17.3 Pseudocode

2001 Prentice Hall, Inc. All rights reserved.

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Chapter 17 - WMLScript: Control Structures I

Outline 17.1 Introduction17.2 Algorithms17.3 Pseudocode17.4 Control Structures17.5 if Selection Structure17.6 if/else Selection Structure17.7 while Repetition Structure17.8 Formulating Algorithms: Case Study 1 (Counter-Controlled Repetition)17.9 Formulating Algorithms with Top-Down, Stepwise

Refinement: Case Study 2 (Sentinel-Controlled Repetition)17.10 Formulating Algorithms with Top-Down, Stepwise

Refinement: Case Study 3 (Nested Control Structures)17.11 Assignment Operators17.12 Increment and Decrement Operators17.13 Note on Data Types17.14 WMLScript Internet and World Wide Web Resources


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17.4 Control Structures

add grade to to tal tota l = tota l + grade;

add 1 to c ounter counter = c ounter + 1;

Fig. 17.1 Flowcharting WMLScript’s sequence structure.


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17.5 if Selection Structure

grade >= 60 true

false

print “Passed”

Fig. 17.2 Flowcharting the single-selection if structure.


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17.6 if/else Selection Structure

grade >= 60

print “Failed” print

Fig. 17.3 Flowcharting the double-selection if/else structure.

“Passed”


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17.7 while Repetition Structure

product <= 1000 produc t = 2 * produc ttrue

fa lse

Fig. 17.4 Flowcharting the while repetition structure.


Outline61 // Fig. 17.6: mean1.wmls

2 // Class average program3 4 extern function average()5 {6 var total = 0; // clear total7 var gradeCounter = 1; // prepare to loop8 var grade; // grade input9 var gradeValue; // number returned by parseInt method10 11 while ( gradeCounter <= 10 ){ // loop 10 times12 grade = Dialogs.prompt( "Enter integer grade", "" );13 14 gradeValue = Lang.parseInt( grade );15 16 total += gradeValue;17 18 ++gradeCounter;19 }20 21 var average = String.format( "%3.2f", ( total / 10 ) );22 23 WMLBrowser.setVar( "classAve", average );24 WMLBrowser.go( "#classAverage" );25 }

Mean1.wmlsLoop 10 times.

Prompt for user input.

Convert the user input to an integer.

Add the value input by the user to the total.Increment the counter.

Calculate the average.


Outline7

1 <?xml version = "1.0"?>2 <!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.2//EN" 3 "http://www.wapforum.org/DTD/wml12.dtd"> 4 5 6 7 8 <wml>9 10 <card id = "index" title = "Class Average Program">11 12 13 <do type = "accept" label = "Enter">14 <go href = "mean1.wmls#average()" />15 </do>16 17 18 Click Enter to enter the grades19 20 </card>21 22 <card id = "classAverage" title = "Class Average">23 24 The class average is: $classAve 25 26 </card>27 </wml>

Fig17_7.wml

Display the class average.


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Outline101 // Fig. 17.9: mean2.wmls

2 // Class average program3 4 extern function average2()5 {6 var total = 0; // clear total7 var gradeCounter = 0; // prepare to loop8 var average;9 10 // prompt for input and read grade from user11 var grade = Dialogs.prompt( "Enter integer grade," + 12 "(-1) to Quit", "" );13 14 // convert grade from a string to an integer15 var gradeValue = Lang.parseInt( grade );16 17 while ( gradeValue != (-1) ) {18 19 // add gradeValue to total20 total = total + gradeValue;21 22 // increment gradeCounter23 ++gradeCounter;24 25 // prompt for input and read grade from user26 grade = Dialogs.prompt( "Enter integer grade, " + 27 "(-1) to Quit", "" );28 29 // convert grade from string to integer30 gradeValue = Lang.parseInt( grade );31 }32

Mean2.wmlsPrompt for user input.

Convert user input to an integer.

Loop until a value of –1 is entered by user.

Add grade entered to total.Prompt for user input.


Outline11

33 // termination phase34 if ( gradeCounter != 0 ) {35 average = 36 String.format( "%3.2f", ( total / gradeCounter ) );37 }38 else {39 average = "No grades were entered";40 }41 42 WMLBrowser.setVar( "classAve", average );43 WMLBrowser.go( "#classAverage" );44 }

Mean2.wmls

Calculate class average.

Display an error message if no grades were entered.


Outline12

1 <?xml version = "1.0"?>2 <!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.2//EN" 3 "http://www.wapforum.org/DTD/wml12.dtd"> 4 5 6 7 8 <wml>9 10 <card id = "index" title = "Class Average">11 12 13 <do type = "accept" label = "Enter">14 <go href = "mean2.wmls#average2()"/>15 </do>16 17 18 Click Enter to enter the grades19 20 </card>21 22 <card id = "classAverage" title = "Class Average">23 24 The class average is: $classAve 25 26 </card>27 </wml>

Fig17_10.wml

Display the class average.


Outline13


Outline14

1 // Fig. 17.12: count.wmls2 // Examination-results program3 4 extern function passFail()5 {6 var passes = 0; // number of passes7 var failures = 0; // number of failures8 var student = 1; // student counter9 10 while ( student <= 10 ) { 11 12 // prompt for user input13 var result = 14 Dialogs.prompt( "Enter result (1 = pass, 2 = fail)", "");15 16 if ( result == "1" ) {17 passes = passes + 1;18 }19 else {20 failures = failures + 1;21 }22 23 student = student + 1;24 }25 26 if ( passes > 8 ) {27 WMLBrowser.setVar( "tooMany", "Raise Tuition" );28 }29 30 WMLBrowser.setVar( "numberPass", passes );31 WMLBrowser.setVar( "numberFail", failures );32 WMLBrowser.go( "#results" );33 }

count.wmlsLoop 10 times.

Prompt for user input.

Update value of passes if a 1 was entered.

Update the value of failures if anything accept a 1 was entered.

Update the counter.


Outline15

1 <?xml version = "1.0"?>2 <!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.2//EN" 3 "http://www.wapforum.org/DTD/wml12.dtd">4 5 6 7 8 <wml>9 10 <card id = "index" title = "Exam Results Program">11 12 13 <do type = "accept" label = "Run">14 <go href = "count.wmls#passFail()" />15 </do>16 17 18 Click Run to run script19 20 </card>21 22 <card id = "results" title = "Results">23 24 25 26 Examination results: 27 Passed: $numberPass 28 Failed: $numberFail 29 $tooMany30 31 </card>32 </wml>

Fig17_13.wml

Display the results.


Outline16


Outline17


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17.12 Increment and Decrement Operators

Assignment operator

Initia l variable value Sample expression

Explanation Assigns

+= c = 3 c += 7 c = c + 7 10 to c

-= d = 5 d -= 4 d = d - 4 1 to d

*= e = 4 e *= 5 e = e * 5 20 to e

/= f = 6 f /= 3 f = f / 3 2 to f

%= g = 12 g %= 9 g = g % 9 3 to g

Fig. 17.14 Arithmetic assignment operators.


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Operator C alled Sample expression Explanation

++ preincrement ++a Increment a by 1, then use the new value of a in the expression in which a resides.

++ postincrement a++ Use the current value of a in the expression in which a resides, then increment a by 1.

-- predecrement --b Decrement b by 1, then use the new value of b in the expression in which b resides.

-- postdecrement b-- Use the current value of b in the expression in which b resides, then decrement b by 1.

Fig. 17.15 The increment and decrement operators.


Outline20

1 // Fig. 17.16: incrementScript.wmls2 // Increment example3 4 extern function increment() 5 {6 var variable1 = 5; // initial variable7 var variable2 = 5; // initial variable8 var post1, post2, post3; // results of increment9 var pre1, pre2, pre3; // results of decrement10 11 12 post1 = variable1;13 post2 = variable1++; // increment14 post3 = variable1;15 16 pre1 = variable2;17 pre2 = ++variable2; // decrement18 pre3 = variable2;19 20 WMLBrowser.setVar( "postResult", post1 );21 WMLBrowser.setVar( "postResult2", post2 );22 WMLBrowser.setVar( "postResult3", post3 );23 WMLBrowser.setVar( "preResult", pre1 );24 WMLBrowser.setVar( "preResult2", pre2 );25 WMLBrowser.setVar( "preResult3", pre3 );26 WMLBrowser.refresh();27 }

IncrementScript.wmls

To begin, the value of variable1 is 5.To begin, the value of variable2 is 5.

Postincrement variable1.

Preincrement variable2.


Outline21

1 <?xml version = "1.0"?>2 <!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.2//EN" 3 "http://www.wapforum.org/DTD/wml12.dtd"> 4 5 6 7 8 <wml>9 10 <card id = "index" title = "Incrementing">11 12 13 <do type = "accept" label = "Run">14 <go href = "incrementScript.wmls#increment()" />15 </do>16 17 18 19 20 Postincrementing: 21 $postResult $postResult2 $postResult3 22 Preincrementing: 23 $preResult $preResult2 $preResult3 24 25 </card> 26 </wml>

Fig17_17.wml

Display the results.


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Operators Assoc iativity Type

() left to right parentheses

++ -- right to left unary

* / % left to right multiplicative

+ - left to right additive

< <= > >= left to right relational

== != left to right equality

?: right to left conditional

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

Fig. 17.18 Precedenc e and assoc ia tivity of the operators d iscussed so far.