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Javascript Tutor - Lesson 10

The while statement.

while (condition)
   do stuff;

Consider the following...


<script type="text/javascript">

function Adder()
   number = 1;
   while (number < 5)
      alert(number + " is less than 5");
      number = number + 1;



<a href="javascript:Adder()">Click here</a>


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...


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...


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" too large or you'll be clicking alert boxes for an hour.)

Here is a solution.

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.)

Here is a solution.

Javascript Tutor
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