Lesson Plan

March 20, 2000

Details

Title	Closer look at looping More statements, alerts, prompts, strings, & math.
Time Allotment	3 hrs

Reading / References

Tutorial 7 - Programming with JavaScript - New Perspectives Manual (NP)

Objectives

Apply our knowledge of looping and arrays
Alert boxes
Prompts
Declare JavaScript externally
Look at some additional statements for more control.
Strings
Math functionality
Date Gotchas

Coursework / Lab Work

Assignment #4 (Checkpoint #3) due
Work through practice exercises

Homework

Checkpoint #3
Assignment #5

Demo

Alert Boxes

alert ("A message to the user");

Prompting the user

var myvariable = prompt("Question goes here?", "Default Value");

External references

Looping through an array – compatibility?

         for count in myArray
         {
                  write(myArray[count]);
         }

Breaking out early

         count = 0;
         while (count < 10)
         {
           if (count == 5)
             break;

           write(count + "...");
           count++;
         }

Jumping to the next iteration
        for iteration in myArray
         {
            if (Math.odd(iteration))
              continue;

            writeln(myArray[iteration]);
         }

Strings
                Concatenation
                String methods
                                i.e. toUpperCase(), toLowerCase
                                changing attributes

Working with the math functions
Math functionality / methods
i.e. abs - absolute value, min, max, etc.

Exercises

EXERCISE 1: BALANCE CALCULATOR

Create a script that calculates the compounded monthly interest on a balance for an entire year. You should define variables for the initial balance and the annual interest rate. Set the variables to 1000 and 12 respectively.

You will need to apply a loop that loops 12 times in order to solve this problem. You will want to create an accumulator variable (name it CurrentBal) to calculate the accrued monthly balance.

*Note that the interest rate is for the whole year. You will want to divide it by 12 and then divide by 100 to make it a percentage.

Each iteration of the loop should perform the calculation, then display the results. After the loop has occurred 12 times, the total should be displayed. Your script should have the following output:

Initial balance: 1000
Interest rate: 12
Month Balance
1     1010
2     1020.1
3     1030.301
4     1040.60401
5     1051.0100501
6     1061.5201506009998
7     1072.1353521070098
8     1082.85670562808
9     1093.6852726843606
10     1104.6221254112042
11     1115.6683466653162
12     1126.8250301319694
Final balance is: 1126.8250301319694

EXERCISE 2: ARRAYS

An array of integers contains both positive and negative numbers. Assume that the negative numbers are undesirable, and we want to get rid of them. Form a NEW array by copying only the positive integers from the original array.

We define and initialize our array of mixed integers:

var Nums = new Array(5,-7,2,9,-22,-57,12,15,83,-45,22,67,-44);

We assign a variable that keeps track of the number of items in the array:

var Counter = 13;

Finally we define our new array that will contain the positive integers. We also need a counter that will hold the next available slot in the new array:

var PosNums = new Array();
var PosNumsIndex = 0;

Our Strategy for copying the positive numbers from Nums to PosNums is to sequentially pass through the array Nums, and each time we arrive at a positive number, copy it to the next available slot in PosNums, then increment the PosNumsIndex:

     for( NumsIndex=0; NumsIndex<Counter; NumsIndex++)
            if(Nums[NumsIndex]>=0)
        PosNums[PosNumsIndex++]=Nums[NumsIndex];

Write the script based on the above description. Once the new array has been formed, the script should display all elements of the new array.

SUPPLEMENTAL EXERCISES

Using the previous exercises as a reference:

Take the updated weight converter add prompts asking the user for input
Add prompts to the area calculator
Add prompts to the record rainfall program
Add prompts to the loop exercise for the balance calculator

Solutions

EXERCISE 1: BALANCE CALCULATOR

<HTML>
<HEAD>
</HEAD>
<BODY>

<SCRIPT LANGUAGE="JavaScript">

</SCRIPT>

</BODY>
</HTML>

EXERCISE 2: ARRAYS

<HTML>
<HEAD>
</HEAD>
<BODY>

<SCRIPT LANGUAGE="JavaScript">

</SCRIPT>

</BODY>
</HTML>

EXERCISE: LOOP EXERCISE WITH PROMPTS

<HTML>
<HEAD>
</HEAD>
<BODY>
<SCRIPT LANGUAGE="JavaScript">

</SCRIPT>

</BODY>
</HTML>