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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.)

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.

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