CX 103: Introduction to Computers
 
 

Lecture 17
 
 


 

Assignment 17


 
 

JavaScript Control Structures

Sequence

Selection

if

if/else

switch

Repetition

while

for

do/while


Repetition with Loops

while ("pre-test") Loops

do/while ("post-test") Loops

for ("counted") Loops
 

Terminology: Each of these loops contains a loop body. It is the loop body that will be executed over and over again.

Each loop will be executed a certain number of times that is governed by a loop control variable (lcv).

Each loop has a test for termination.
 
 

Any repetition carried out by one of these methods can be modified to be done by the other two methods.


 
 

while Loops

The while loop has the form:

while ( some boolean condition)

{ body of loop }

The body of the loop is executed as long as the Boolean condition is true.

When Boolean becomes false, the loop terminates and execution continues with the code following the loop.

The test for termination occurs "at the top" of the loop, before the body is executed. It is possible that the loop may not be executed at all.

You must update the lcv yourself.

do/while Loops

The form of the do/while loop is:

do

{ body of loop }

while (some Boolean condition)

Test for termination is "at the bottom."

The loop body will be executed at least once.

The loop body will be performed as long as the Boolean condition is true.

You must update the lcv yourself.
Example:

N = 1;

do

document.writeln("I Love JavaScript.");

N = N + 1;

while (N <= 100)


 
 

Application of a do/while Loop

<HTML>

<HEAD>

<TITLE>User Friendly Input</TITLE>

<! ForceUpperCase.html

Forces User to Enter UpperCase Letters -->

<SCRIPT LANGUAGE = "JavaScript">

var valid, Character ;

valid = false;

do

{

Character = window.prompt("Enter UPPERCASE Letter", "");

document.writeln("<H2>" + Character);

if ( (Character >= 'A') && (Character <= 'Z') ) valid = true;

}

while (valid == false);
 
 

</SCRIPT>

</HEAD>

<BODY BGCOLOR = "beige">

</BODY>

</HTML>

ForceUpperCase.html

for Loops

easiest to use:

test for termination and

updating of loop control variable

are automatically handled
 

Basic form of for Loop:

for ( lcv initialization; loop continuation condition; lcv update)

{ body of loop }

Example:

var i;

for ( i = 1; i <= 100; i = i+1)

document.writeln("Get Rid of SUV's Now!");
 
 

Example: Find sum of first 200 positive integers:

var i, sum;

sum = 0;

for (i = 1; i <= 200; i = i + 1)

sum = sum + i;

document.writeln(sum);
 
 
 
 

Example: Find sum of all the even numbers from 2 to 200:

var i, sum;

sum = 0;

for (i = 2; i <= 200; i = i + 2)

sum = sum + i;

document.writeln(sum);
 



 

Application of a for Loop

How Much will it Cost to Attend Midd?

<HTML>

<! Homer Simpson March 23, 2001

HomerSimpson/Middfee.html

This Program Projects The Middlebury College Comprehensive Fee Forward 30 years assuming a constant percentage increase -->

<HEAD>

<TITLE>Middlebury's Projected Comprehensive Fee</TITLE>

<SCRIPT LANGUAGE = "JavaScript">
 
 

Fee = 32765;

GrowthRate = 0.047;

for (Year = 2000; Year <= 2030; Year = Year+1)

{

document.writeln("<H2>"+Year + ": $" + Fee + "<BR>");

Fee = Fee + Fee*GrowthRate;

}

</SCRIPT>

</HEAD>

<BODY BGCOLOR = "white">

</BODY>

</HTML>
MiddFee.html

<HTML>

<HEAD>

<TITLE>Middlebury's Projected Comprehensive Fee</TITLE>

<! Homer Simpson March 23, 2001

HomerSimpson/MiddFee2.html

An improvement over MiddFee

Rounds Fee to nearest dollar ->

<SCRIPT LANGUAGE = "JavaScript">
 
 

Fee = 32765;

GrowthRate = 0.047;

document.writeln("<H1>Middlebury's Projected Fee</H1>");

for (Year = 2000; Year <= 2030; Year = Year+1)

{

document.writeln("<H2>"+Year + ": $" + Math.round(Fee) + "<BR>");

Fee = Fee + Fee*GrowthRate;

}

</SCRIPT>

</HEAD>

<BODY BGCOLOR = "white">

</BODY>

</HTML>

MiddFee2.html

<HTML>

<HEAD>

<TITLE>Middlebury's Projected Comprehensive Fee</TITLE>

<! Homer Simpson March 23, 2001

HomerSimpson/MiddFee3.html

Uses a table to display projected Comprehensive Fee ->

<SCRIPT LANGUAGE = "JavaScript">

Fee = 32765;

GrowthRate = 0.047;

document.writeln("<H1>Middlebury's Projected Fee </H1>");

document.writeln( "<TABLE BORDER = '1' >");

document.writeln( "<TR><TD WIDTH = '100'>Year</TD>" );

document.writeln( "<TD><B>Comprehensive Fee</B></TD>" );
 
 

for (Year = 2000; Year <= 2030; Year = Year+1)

{ document.writeln("<TR><TD>" +Year + "</TD><TD>"+ "$" + Math.round(Fee) + "</TD></TR>" );

Fee = Fee + Fee*GrowthRate;

}
 
 

document.writeln( "</TABLE>");

</SCRIPT>

</HEAD>

<BODY BGCOLOR = "linen">

</BODY>

</HTML>

MiddFee3.html


 

Selection

if

if/else

switch


 

<HTML>

<HEAD>

<TITLE>Pick a College </TITLE>

<SCRIPT LANGUAGE = "JavaScript">

where = window.prompt("Where do you want to go to College? Enter Middlebury, Carleton,Williams, Amherst or Dartmouth","");

switch( where) {

case "Middlebury" :

alert("Great Choice!!!");

window.location = "http://www.middlebury.edu";

break;

case "Carleton":

alert("Not bad, but very far away");

window.location = "http://www.carleton.edu";

break;

case "Williams":

alert("Boo, Hiss");

window.location = "http://www.williams.edu";

break;

case "Amherst":

alert("Are you kidding? Too preppie");

window.location = "http://www.amherst.edu";

break;

case "Dartmouth":

alert("Party School");

window.location = "http://www.dartmouth.edu";

break;

default:

document.writeln("Not available");

}

</SCRIPT>

</HEAD>

<BODY BGCOLOR = "white">

</BODY>

</HTML>

CollegeChoice.html
 


First Encryption Idea

1) Break Text into 2 character blocks

2) Change each block into a 4 digit number using ASCII Values

3) Add 7 (mod 10) to each digit

4) Swap first digit with fourth digit

5) Swap second digit with third digit

6) Transmit new 4 digit number
 
 

Example

text: CX 103

2 character blocks: CX_1 03

Change to 4 digits: 6788 3249 4851

Add 7 (mod 10) to each digit

6788 3249 4851

7777 77777777

3455 0916 1528

Swap digits

5543 6190 8251

Send message as 554361908251
 
 
 

What You Can Do On Your Spring Break