JavaScript Control Statements II

IPA
1st
Semester, 2007-2008
Internet 1
Ch. 10
JavaScript: Control
Statements II
attasr@ipa.edu.sa

09/30/15 © Reem Al-Attas 2
Essentials of Counter-Controlled
Repetition
Counter-controlled repetition requires
 Control variable (loop counter)
 Initial value of the control variable
 Increment or decrement the control variable
through the loop
 Condition to test the final value of the control
variable

WhileCounter.html
(1 of 2)
1 <?xml version = "1.0"?>
2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
4
5 
6 
7
8 <html xmlns = "http://www.w3.org/1999/xhtml">
9 <head>
10 <title>Counter-Controlled Repetition</title>
11
12 <script type = "text/javascript">
13 
23 </script>
24

25 </head><body></body>
26 </html>

for Repetition Statement
 for repetition statement
 Handles all the details of counter-controlled
repetition
 for structure header

for ( var counter = 1; counter <=7; ++counter )
Initial value of control variable Increment of control variable
Control variable name Final value of control variable
for which the condition is true
forkeyword
Loop-continuation condition
Fig. 9.3 for statement header components.

ForCounter.html
(1 of 1)
4
5 
6 
7
9 <head>
10 <title>Counter-Controlled Repetition</title>
11
13 
22 </script>
23
25 </html>

counter <= 7
document.writeln(
"<p style="font-size: "
+ counter +
"ex">XHTML font size " +
counter + "ex</p>" );
true
false
var counter = 1
++counter
Establish
initial value
of control
variable.
Determine
if final value
of control
variable
has been
reached.
Body of loop
(this may be many
statements)
Increment
the control
variable.
Fig. 9.4 for repetition structure flowchart.

General Format of:
 For
for (initialization;
loopContiuationTest;
increment)
statement;
 While
initialization;
while
(loopContiuationTest)
{
increment;
statement;
}

Examples Using the for
Statement
Book Sec 9.4.
Summation with for
Compound interest calculation with for
loop
 Math object
 Math.pow
 Math.round

Sum.html
(1 of 1)
4
5 
6 
7
9 <head>
10 <title>Sum the Even Integers from 2 to 100</title>
11
13 
22 </script>
23
25 </html>

Interest.html
(1 of 2)
4
5 
6 
7
9 <head>
10 <title>Calculating Compound Interest</title>
11
13 <!--
14 var amount, principal = 1000.0, rate = .05;
15
16 document.writeln(
17 "<table border = "1" width = "100%">" );
19 "<caption>Calculating Compound Interest</caption>" );
21 "<thead><tr><th align = "left">Year</th>" );
23 "<th align = "left">Amount on deposit</th>" );
24 document.writeln( "</tr></thead>" );
25

Interest.html
(2 of 2)
26 for ( var year = 1; year <= 10; ++year ) {
27 amount = principal * Math.pow( 1.0 + rate, year );
28 document.writeln( "<tbody><tr><td>" + year +
29 "</td><td>" + Math.round( amount * 100 ) / 100 +
30 "</td></tr>" );
31 }
32
33 document.writeln( "</tbody></table>" );
34 // -->
35 </script>
36
38 </html>

switch Multiple-Selection
Statement
Controlling expression
Case labels
Default case

SwitchTest.html
(1 of 3)
4
5 
6 
7
9 <head>
10 <title>Switching between XHTML List Formats</title>
11
13 <!--
14 var choice, // user’s choice
15 startTag, // starting list item tag
16 endTag, // ending list item tag
17 validInput = true, // indicates if input is valid
18 listType; // list type as a string
19
20 choice = window.prompt( "Select a list style:n" +
21 "1 (bullet), 2 (numbered), 3 (lettered)", "1" );
22

SwitchTest.html
(2 of 3)
23 switch ( choice ) {
24 case "1":
25 startTag = "<ul>";
26 endTag = "</ul>";
27 listType = "<h1>Bullet List</h1>";
28 break;
29 case "2":
30 startTag = "<ol>";
31 endTag = "</ol>";
32 listType = "<h1>Ordered List: Numbered</h1>";
33 break;
34 case "3":
35 startTag = "<ol type = "A">";
36 endTag = "</ol>";
37 listType = "<h1>Ordered List: Lettered</h1>";
38 break;
39 default:
40 validInput = false;
41 }
42
43 if ( validInput == true ) {
44 document.writeln( listType + startTag );
45
46 for ( var i = 1; i <= 3; ++i )
47 document.writeln( "<li>List item " + i + "</li>" );

SwitchTest.html
(3 of 3)
48
49 document.writeln( endTag );
50 }
51 else
52 document.writeln( "Invalid choice: " + choice );
53 // -->
54 </script>
55
56 </head>
57 <body>
58 <p>Click Refresh (or Reload) to run the script again</p>
59 </body>
60 </html>

switch Multiple-Selection Statement
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

do…while Repetition Statement
Similar to the while statement
Tests the loop continuation condition after
the loop body executes
Loop body always executes at least once

DoWhileTest.html
(1 of 2)
4
5 
6 
7
9 <head>
10 <title>Using the do...while Repetition Statement</title>
11
13 
24 </script>

25
27 </html>

do…while Repetition Structure
condition
true
action(s)
false
Fig. 9.10 do…while repetition statement flowchart.

General Format of do…while
initialization;
do {
statement;
increment;
} while
(loopContiuationTest);
 While
initialization;
while
(loopContiuationTest)
{
increment;
statement;
}

break and continue Statements
 break
 Immediate exit from the structure
 Used to escape early from a loop
 Skip the remainder of a switch statement
 continue
 Skips the remaining statements in the body of
the structure
 Proceeds with the next iteration of the loop

BreakTest.html
(1 of 2)
4
5 
6 
7
9 <head>
10 <title>
11 Using the break Statement in a for Structure
12 </title>
13
15 <!--
16 for ( var count = 1; count <= 10; ++count ) {
17 if ( count == 5 )
18 break; // break loop only if count == 5
19
20 document.writeln( "Count is: " + count + "<br />" );
21 }
22

24 "Broke out of loop at count = " + count );
25 // -->
26 </script>
27
29 </html>

ContinueTest.html
(1 of 2)
4
5 
6 
7
9 <head>
10 <title>
11 Using the continue Statement in a for Structure
12 </title>
13
15 <!--
16 for ( var count = 1; count <= 10; ++count ) {
17 if ( count == 5 )
18 continue; // skip remaining code in loop
19 // only if count == 5
20
21 document.writeln( "Count is: " + count + "<br />" );
22 }
23

24 document.writeln( "Used continue to skip printing 5" );
25 // -->
26 </script>
27
29 </html>

Labeled break and continue Statements
 Labeled break statement
 Break out of a nested set of structures
 Immediate exit from that structure and enclosing
repetition structures
 Execution resumes with first statement after enclosing
labeled statement
 Labeled continue statement
 Skips the remaining statements in structure’s body
and enclosing repetition structures
 Proceeds with next iteration of enclosing labeled
repetition structure
 Loop-continuation test evaluates immediately after the
continue statement executes

4
5 
6 
7
9 <head>
10 <title>Using the break Statement with a Label</title>
11
13 <!--
14 stop: { // labeled block
15 for ( var row = 1; row <= 10; ++row ) {
16 for ( var column = 1; column <= 5 ; ++column ) {
17
18 if ( row == 5 )
19 break stop; // jump to end of stop block
20
21 document.write( "* " );
22 }
23
24 document.writeln( "<br />" );
25 }

26
27 // the following line is skipped
28 document.writeln( "This line should not print" );
29 }
30
31 document.writeln( "End of script" );
32 // -->
33 </script>
34
36 </html>

4
5 
6 
7
9 <head>
10 <title>Using the continue Statement with a Label</title>
11
13 <!--
14 nextRow: // target label of continue statement
15 for ( var row = 1; row <= 5; ++row ) {
16 document.writeln( "<br />" );
17
18 for ( var column = 1; column <= 10; ++column ) {
19
20 if ( column > row )
21 continue nextRow; // next iteration of
22 // labeled loop
23
24 document.write( "* " );
25 }

ContinueLabelTest.html
(2 of 2)
26 }
27 // -->
28 </script>
29
31 </html>

Logical Operators
More logical operators
 Logical AND ( && )
 Logical OR ( || )
 Logical NOT ( ! )

Logical Operators
expression1 expression2 expression1 &&
expression2
false false false
false true false
true false false
true true true
Fig. 9.15 Truth table for the && (logical AND)
operator.

Logical Operators
expression1 expression2 expression1 ||
expression2
false false false
false true true
true false true
true true true
Fig. 9.16 Truth table for the || (logical OR) operator.
expression !expression
false true
true false
Fig. 9.17 Truth table for operator ! (logical negation).

4
5 
6 
7
9 <head>
10 <title>Demonstrating the Logical Operators</title>
11
13 <!--
15 "<table border = "1" width = "100%">" );
16
18 "<caption>Demonstrating Logical " +
19 "Operators</caption" );
20
22 "<tr><td width = "25%">Logical AND (&&)</td>" +
23 "<td>false && false: " + ( false && false ) +
24 "<br />false && true: " + ( false && true ) +
25 "<br />true && false: " + ( true && false ) +

26 "<br />true && true: " + ( true && true ) +
27 "</td>" );
28
30 "<tr><td width = "25%">Logical OR (||)</td>" +
31 "<td>false || false: " + ( false || false ) +
32 "<br />false || true: " + ( false || true ) +
33 "<br />true || false: " + ( true || false ) +
34 "<br />true || true: " + ( true || true ) +
35 "</td>" );
36
38 "<tr><td width = "25%">Logical NOT (!)</td>" +
39 "<td>!false: " + ( !false ) +
40 "<br />!true: " + ( !true ) + "</td>" );
41
42 document.writeln( "</table>" );
43 // -->
44 </script>
45
47 </html>

Logical Operators
Operator Associativity Type
++ -- ! right to left unary
* / % left to right multiplicative
+ - left to right additive
< <= > >= left to right relational
== != left to right equality
&& left to right logical AND
|| left to right logical OR
?: right to left conditional
= += -= *= /= %= right to left assignment
Fig. 9.19 Precedence and associativity of the operators discussed
so far.

Summary of Structured
Programming
Flowcharts
 Reveal the structured nature of programs
Single-entry/single-exit control structures
 Only one way to enter and one way to exit each
control structure
Control structure stacking
 The exit point of one control structure is
connected to the entry point of the next control
structure

Programming
T
F
whilestatement
T
F
for
T
F
do…while
Repetition
Fig. 9.20 Single-entry/single-exit sequence, selection and repetition structures. (1 of 3)
statement
statement

Summary of Structured Programming
break
T
F
ifstatement
(singleselection)
TF
if…else
(doubleselection)
T
F
switch
(multipleselection)
T
F
T
F
.
.
.
Selection
break
break
Fig. 9.20 Single-entry/single-exit sequence, selection and repetition structures. (2 of 3)
statement
statement

ProgrammingSequence
.
.
.Fig. 9.20 Single-entry/single-exit sequence, selection and repetition structures. (3 of 3)

Programming
Rules for Forming Structured Programs
1) Begin with the “simplest flowchart” (Fig. 9.22).
2) Any rectangle (action) can be replaced by two rectangles (actions) in sequence.
3) Any rectangle (action) can be replaced by any control structure (sequence, if, if…else,
switch, while, do…while or for).
4) Rules 2 and 3 may be applied as often as you like and in any order.
Fig. 9.21Rules for forming structured programs.

Programming
Fig. 9.22 Simplest flowchart.

.
.
.
Rule 2 Rule 2 Rule 2
Fig. 9.23 Repeatedly applying rule 2 of Fig. 9.21 to the simplest flowchart.

Rule 3
Rule 3
Fig. 9.24 Applying rule 3 of Fig. 9.21 to the simplest flowchart.

Stacked building blocks Nested building blocks
Overlapping building blocks
(Illegal in structured programs)
Fig. 9.25 Stacked, nested and overlapped building blocks.

Programming
Fig. 9.26 Unstructured flowchart.

Assignment 7
 1) Exercise # 9.9 &
 2) Exercise # 9.14 in
the text book.
Due Date for A # 7:
 Monday before your
lecture.

JavaScript Control Statements II

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