Last Row of Buttons
Five, Four, Tip...
On to the last line of buttons. This one gets a little tricky, so let's take it by itself.
See it in action
Here's the code
(It's big. Get it all.)
The last line of buttons look like this:
Zero, decimal, + sign, equals, square root, random, Pi

Here are the actual button codes without all the table coding:
<INPUT TYPE=BUTTON VALUE=" 0 " NAME="but0"
onClick="document.calculator.text.value+='0'">
<INPUT TYPE=BUTTON VALUE=" . " NAME="decimal"
onClick="document.calculator.text.value+='.'">
<INPUT TYPE=BUTTON VALUE=" + " NAME="sign" onClick="change()">
<INPUT TYPE=BUTTON VALUE=" = " NAME="equals"
onClick="document.calculator.text.value=eval(document.calculator.text.value)">
<INPUT TYPE=BUTTON VALUE=" x= " NAME="sqrt"
onClick="document.calculator.text.value=Math.sqrt(document.calculator.text.value)">
<INPUT TYPE=BUTTON VALUE=" rand " NAME="random"
onClick="document.calculator.text.value = getRandom()">
<INPUT TYPE=BUTTON VALUE=" pi " NAME="pi"
onClick="document.calculator.text.value+= getPi()">


Allow me to take them a little out of order. You've seen some of the formats before, so I'll hit them first.
Zero & Decimal
<INPUT TYPE=BUTTON VALUE=" 0 " NAME="but0" onClick="document.calculator.text.value+='0'">
<INPUT TYPE=BUTTON VALUE=" . " NAME="decimal" onClick="document.calculator.text.value+='.'">


Look familiar? It should. Both of these buttons act like the other number buttons, one through nine. You click and a 0 is placed in the display. You click and a decimal point is placed in the display.
Again, notice the use of += to add the number to the display rather than replacing what is already displayed.
Square Root
<INPUT TYPE=BUTTON VALUE=" x= " NAME="sqrt"
onClick="document.calculator.text.value=Math.sqrt(document.calculator.text.value)">


Just as before, the number displayed is acted upon through the Math object and the command "sqrt" to create the result.
In case you're wondering, "x½" is the ascii code to display x½. Cool, huh?
Random
<INPUT TYPE=BUTTON VALUE=" rand " NAME="random"
onClick="document.calculator.text.value = getRandom()">


A function. For this random button, and the Pi button that follows, the author decided to go with a function. Note in the code how the display (document,calculator.text.value) is created by going to the function
getRandom(), which looks like this:
function getRandom()
{return Math.random()}


The function simply returns (return) a random number (created through Math.random) to the display. It seems simple enough, but you might ask why not just follow the same format for putting it all in the onClick? I guess you could, but I would think the author set this aside as a function because the random number had nothing to do with the display. By setting it in a function he separated it from any other numbers. It's probably a good idea.
Pi
<INPUT TYPE=BUTTON VALUE=" pi " NAME="pi" onClick="document.calculator.text.value+= getPi()">

Same as above. The number for Pi is returned from a function that looks like this:
function getPi()
{return Math.PI}


Again, could the author have simply done it inside the button itself? Yes. This, I think, is just a cleaner method of doing it. Plus, Pi has a decimal point in it and that's tough to get into a simple display. Doing this solved that problem pretty quickly.
Equals
<INPUT TYPE=BUTTON VALUE=" = " NAME="equals"
onClick="document.calculator.text.value=eval(document.calculator.text.value)">


Ah, now we get to the meat of the calculator function, the equal button. You push this one, you get the answer. How you get the answer is a matter of how the author set up the script.
Remember earlier in the script, the majority of the buttons simply set numbers or operators (+, , /, *) into the display? You clicked on the numbers and they displayed one right after the other so that when you were done putting in all of your numbers, the equation you entered appeared there in the display.
The equals button simply says "Do it!" after you've entered in the numbers. There in the display is a math equation. Click the equal button and that equation is evaluated (eval) and the result is placed into the display. Poof! Your answer! And you thought it was hard....
There's one more button to worry about. It's the one that changes a number from negative to positive or the other way around. It's clever and it will be a Script Tip unto itself.
Next Time: Positive to Negative
This article was originally published on September 7, 1999