Javascript Tutor
- Lesson 19
The for statement.
The for statement is a very useful tool. Here is an example...
<HTML>
<HEAD>
<TITLE></TITLE>
<SCRIPT language="Javascript"><!--
function boxPopper()
{
for (var x = 0; x < 5; x++)
{
alert(x);
}
}
//--></SCRIPT>
</HEAD>
<BODY>
<A HREF="javascript:boxPopper()">Click here</A>
</BODY>
</HTML>
Try it.
Here's what's happening...
for ( x = 0; x < 5; x++ ) - x starts at 0
for ( x = 0; x < 5; x++ ) - if x is less than
5, execute the instructions in the brackets once... alert(x);
for ( x = 0; x < 5; x++ ) - increment x by one
and go to step 2
The loop stops when x is no longer less than 5. (You might be thinking... hey,
the loop stopped after 4! To which I ask you... is 5 less than 5? If you say
yes, keep thinking about it until you say no ;-)
Exercise: Come up with a script that calculates the square root of each
integer from 0 to 20, rounds each to one decimal point and displays them in
an alert box like so...
The square root of 0 is 0
The square root of 1 is 1
The square root of 2 is 1.4
etc...
Hint: you can specify a line break in an alert box with an escaped n
(n for newline) - \n...
alert("Hand\nhand\nfingers\nthumb");
- try it
Again, it's a tough one. Hey, if they were easy you wouldn't learn anything,
right?
Exercise: Make a slight alteration to that last exercise and have it
round to two decimal places.