Javascript Tutor
- Lesson 10
The while statement.
while (condition)
{
do stuff;
}
Consider the following...
<HTML>
<HEAD>
<TITLE></TITLE>
<SCRIPT language="javascript"><!--
function Adder()
{
number = 1;
while (number < 5)
{
alert(number + " is less than 5");
number = number + 1;
}
}
//--></SCRIPT>
</HEAD>
<BODY>
<A HREF="javascript:Adder()">Click here</A>
</BODY>
</HTML>
Try it.
See what's going on here? Study the example until you do.
"While" we're here, there's a little programming shortcut you might
be interested in. It is very common to increment or decrement a number by 1.
In the last example we wrote it as...
number = number + 1;
This can also be written as...
number++;
You'll see this a lot in javascript, plus it's fairly common in other programming
languages as well.
The same shorthand can also be used for subtraction...
number--;
is the same as
number = number - 1;
Exercise: Alter the example above to prompt the user for both the first
and last number. And use the number++ shorthand notation. (When you run this,
I wouldn't make your "spread" to large or you'll be clicking alert
boxes for an hour.)
Notice I multiplied the prompt box by 1. This is so that all entries are forced
into being numbers before we do anything with them. If we left that out, multi-digit
numbers such as 12 are sometimes considered strings rather than numbers.
Exercise: Alter your last exercise to check if the second number is larger
than the first. If it's not, inform the user and have him try again. (Hint:
You'll need to add an if-else statement in there.)