tik-20 computer and information science

TIK-20 Computer and Information Science

April 3, 2009

1TIK20 - West Hill C.I. - Spring 2009

Lesson 7a: Conditional Loops Homework

1. A program accepts the price of a new car, trade-in-allowance, and down payment, and then tells how much is owing on the car. The program continues to ask the user if he/she would like to continue entering values (with a confirm dialogue box--see script examples for an explanation of what they are and how they work) and continues to perform the calculations if the user clicks OK, but exits if the person clicks CANCEL.



• Write a program segment containing a loop for a program that accepts the number of words in a classified ad as input and calculates the price of the ad based on the following criteria (using selection statements):

The output should be in the following format: The West Hill Classifieds The cost of your classified ad is $__________. The loop should continue to accept values until the user clicks CANCEL at the

confirm dialogue box prompt.

TIK20 - West Hill C.I. - Spring 2009 3

Number of Words Price

1 to 50 words $25.00

51 to 100 words $45.00

101 to 200 words $75.00

Today’s Agenda

1. >,<,>=,<=,==,!=2. for, while3. IPO and Lesson 7a Homework4. DO (1) and (2) at your workstations5. Show Mr. Robinson or Ms. Jansen that your

programs are working before you leave.


A=1; B=1; C=2; D=2; E=3

Tell me if the following are true or false

A > B || C >= D true or false

B < C && C != D true or false

A <= B || B == E true or false


For loops

Recall for loops from last class…

for (i = 0; i < 5; i++){ document.write(i + “<BR>”)}


Now the while loop

Easier to use than the for loop is the while loop.

A while loop doesn't initialize or increment any fields automatically as part of the command.

It just tests a condition and executes the loop for as long as the condition remains true.


Let's begin by looking at a simple while statement:

x = 0 // initialize before the loopwhile (x<10) { document.write(x + "<BR>") x++; // increment the variable inside loop}


Common errors


Forget to do something to the value that is being tested. What’s wrong here?

x = 0 // initialize before the loopwhile (x<10) { document.write(x + "<BR>")}

Do while loop

The “test” goes to the bottom of the loop:

x = 12do {

document.write(x)x++

} while (x<10)


Do while loop - note

In this example the loop will execute once even though the original value of x is greater than that tested for in the while condition.


Back to Lesson 7a

Recall an IPO

Input: Input from the keyboard

Processing: Operations carried out by the computer

Output: Variables (storing data) that will be output to the screen


Question from HomeworkA program accepts the price of a new car, trade-in-

allowance, and down payment, and then tells how much is owing on the car. The program continues to ask the user if he/she would like to continue entering values (with a confirm dialogue box--see script examples for an explanation of what they are and how they work) and continues to perform the calculations if the user clicks OK, but exits if the person clicks CANCEL.


Translate to Javascript

response = “”// Cancel button pressed??? while(response != null){ document.write(response) response=prompt("How are you today? ","")}



• Write a program segment containing a loop for a program that accepts the number of words in a classified ad as input and calculates the price of the ad based on the following criteria (using selection statements):

The output should be in the following format: The West Hill Classifieds The cost of your classified ad is $__________. The loop should continue to accept values until the user clicks CANCEL at the

confirm dialogue box prompt.


Number of Words Price

1 to 50 words $25.00

51 to 100 words $45.00

101 to 200 words $75.00

tik-20 computer and information science

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