CS 101 - Lab 9

Due at the end of lab session during the 10th week

Arrays

This week we are going to look at arrays in JavaScript and some typical operations performed on arrays. This will also allow us to use the for loop. There are three ways to create an array:

• arrayName = new Array ()

• arrayName = new Array (arrayLength)

• arrayName = new Array (firstValue, secondValue, ... , lastValue)

The first method creates an array but the number of elements in the array (which is also called the length) is unknown. As elements are added into the array the length of the array is modified. This type of array usage is very uncommon in other languages, so we won't discuss it.

The second and third methods are much more common. The second method creates a array of length of "arrayLength" but no values are stored into the array. The third value create and initializes an array. The length of the array is equal to the number of values listed.

Lab Assignment

Turn in the JavaScript/HTML code that does the following to the Digital Drop Box:

Create a JavaScript program that has one button and 6 text fields. When the button is clicked perform the following tasks:

• Generate 10 random numbers and store them into an array (see below).

• Calculate the average of the array values and display that in the first text field.

• Determine the smallest value in the array and display it in the second text field.

• Determine the largest value in the array and display it in the third text field.

• Determine the number of array values that are equal to the average and display that number in the fourth text field.

• Determine the number of array values that are less than the average and display that number in the fifth text field.

• Determine the number of array values that are greater than the average and display that number in the sixth text field.

Remember that the subscript values for the array (also called the index values) start with the value of zero and end with the length of the array - 1. So an array with length of 10 has it subscript values in the range of 0 to 9.

When writing your code, the easiest way to do this is to use a for loop. Set up the for loop so that the loop variable has the value of a different subscript each time through the loop. The loop variable can then be used to access one element in the array each time though the loop. For example the following code will store 10 different random numbers in an array of length 10. Note the declaration of variables is not shown.

// generate 10 random numbers and store them in "array"

for (i = 0; i < 10; i++)

{

array[i] = Math.random()

}