7.1  Java Script - Variables

Index Code Tester

OBJECTIVE

DISCUSSION

Variables

Variable Types

Type Description Examples
Integer

Holds whole numbers, positive or negative

iCount = 23

iTemp = -11

Float Holds real numbers (numbers with decimal points, positive or negative)

fTemp = 98.6

fAvogadro = 6.02E23

String Holds characters

sName = "Me"

sAddress = "100 Kenwood Ave"

Boolean Only true or false. Can use 0 to represent false and 1 to represent true. bFlag = true

Demo - Variable Types

Naming Conventions

Constants

Scope - Global vs Local Variables

Demo - Global and Local Variables 

EXERCISES

1.  Which of the following names are NOT valid? num, num1, 1num, _num, n&um, iNum, num 1. 

2.  Write statements to declare and initialize variables to...

  1. Store the name of someone.  Initialize it to your name.
  2. Store the number of students in a class.  Initialize it to the number in this class.
  3. Store your class average.
  4. Store whether or not a number is maximum.  Initialize it to "false".

3.  Explain the difference between a global and local variable.  Which is preferred? Where is each declared?

4.  Give examples of when you would use a local variable and a global variable.

5.  The purpose of this exercise is to determine what happens when you add variables of different types.  For example, what will be the result of adding a string to a boolean?  You will answer this question by creating a page that has 8 variables declared and initialized in a <script> block in the <head>.  There should be two variables of each type. Then you should create a table as shown below.  In each of the empty cells, the variable from the column and row should be added and written into the cell using document.write.

iX = 2 fX = 3.14 sX = "jo" bX = true
iY = 4
fY = 2.2
sY = "bob"
bY = false

6.  Create a program to demonstrate how global variables can be accessed from all functions.  Make sure that your page meets the following requirements:

  1. It has a textbox, a button labelled "Assign" and a button labelled "Display".
  2. It has a variable declared globally in the <script> block.
  3. It has a function called assign().  In this function, the value from the textbox should be assigned to the global variable.
  4. It has a function called display().  In this function, the global variable is displayed in an alert. 
  5. When the user clicks the "Assign" button, the function assign() is called.
  6. When the user clicks on the "Display" button, the function display() is called.

7. Create a program to demonstrate how local variables can NOTbe accessed from all functions.  Make sure that your page meets the following requirements:

  1. It has a textbox, a button labelled "Assign" and a button labelled "Display".
  2. It has a function called assign().  In this function a variable is declared and assigned the value from the textbox.
  3. It has a function called display().  In this function, the variable in the function assign() is displayed in an alert. 
  4. When the user clicks the "Assign" button, the function assign() is called.
  5. When the user clicks on the "Display" button, the function display() is called.

 8.  Determine the largest possible value for a float.  You can either search the Internet or create a program.

LINKS AND HELP

http://www.w3schools.com/js/js_variables.asp
http://www.southwest.com.au/~jfuller/javascript/javascript4.htm