First Post, please help me with this script

**AhmedScript** · 07-10-2012 08:16 AM

<!DOCTYPE>
<html><head>
<title>Chapter Two</title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8" />
<script type="text/javascript">
/*<CDATA[[*/

var guestsCost=0;
var limousinesCost=0;
var liveMusicCost=0;
var flowersCost=0;
var totalEstimate=0;

function calcGuests(){
totalEstimate -= guestsCost;
guestsCost = document.details.numGuests.value * 65;
totalEstimate += guestsCost;
document.estimate.cost.value = "$" + totalEstimate;
}
/*]]>*/
</script>
</head>

<body>
<form action="" name="details">
<table border="1">
<tr>
<td>Guests<br />
($65 each)</td>
<td>
<input type="text" name="numGuests" size="5" onchange="calcGuests();" /></td>
</tr>
</table>

</form>
<form action="" name="estimate">
<p>
<input type="text" name="cost" size="5"
style="border-style: none; border-color: inherit border-width: medium; background-color: yellow; text="0" /></p>
</form>

</body>
</html>

I didn't understand what the second statement (totalEstimate -= guestsCost

in the "calcGuests" function is for?
Please someone explain to me as I'm a beginner.

Thanks in Advance!

**payukim** · 07-10-2012 10:27 AM

(totalEstimate -= guestsCost) = (totalEstimate=totalEstimate-guestsCost)

or it means subtract "total estimate" by "guest cost" and save the result in "total estimate".

**AhmedScript** · 07-10-2012 01:29 PM

Originally Posted by payukim

(totalEstimate -= guestsCost) = (totalEstimate=totalEstimate-guestsCost)

or it means subtract "total estimate" by "guest cost" and save the result in "total estimate".

Thank u for u quick reply.

I changed the value of the variable totalEstimate and assigned it a value of 5 as : var totlaEstimate = 5;

Now, if, lets say, I type 1 in the textbox.. I got a result of of 70?

Please, if possible, explain to me the whole process/calculations that are taking place and how?

**Padonak** · 07-10-2012 04:51 PM

Code:

var guestsCost=0;
 var limousinesCost=0;/* this variable does nothing */
 var liveMusicCost=0;/* this variable does nothing */
 var flowersCost=0;/* this variable does nothing */
 var totalEstimate=0;

 function calcGuests(){
 totalEstimate -= guestsCost; /* for the very first calculation this line has no sense because it is equal to 'totalEstimate = 0 - 0;' */
 guestsCost = document.details.numGuests.value * 65;/* this means 'guestsCost = here_goes_what_you_type_in_the_first_form_input * 65' */
 totalEstimate += guestsCost;/* this is equal to 'totalEstimate = totalEstimate + guestsCost' */
 document.estimate.cost.value = "$" + totalEstimate;/* this makes a string from the dollar sign and the calculation result and puts it into the second form's INPUT element named 'COST' */
 }

**dororo** · 07-10-2012 08:43 PM

totalEstimate -= guestsCost;

first time,it's mean totalEstimate = totalEstimate-guestsCost;// totalEstimate=0-0;
result:
totalEstimate=0+first time input numGuest*65;
second time,your change the input numGuests,the js will run again,but the varables is global,
totalEstimate!=0
totalEstimate=first time input numGuest*65+second time input numGuest*65;//wrong answer!
you must make totalEstimate=0 as the first time

**payukim** · 07-11-2012 01:16 AM

Originally Posted by AhmedScript

Thank u for u quick reply.

I changed the value of the variable totalEstimate and assigned it a value of 5 as : var totlaEstimate = 5;

Now, if, lets say, I type 1 in the textbox.. I got a result of of 70?

Please, if possible, explain to me the whole process/calculations that are taking place and how?

Yes, you will get 70 as the result. Because:

Let's say, you declare:

guestsCost=0
totalEstimate = 5

Then you type 1 as the value in the text box name = numGuests

After that it will call the function calcGuests() as you have onchange="calcGuests()" in the text box

In the function, it does:

totalEstimate -= guestsCost means totalEstimate = 5-0; totalEstimate now = 5

guestsCost = document.details.numGuests.value * 65 means guestsCost = 1*65; guestsCost now = 65

totalEstimate += guestsCost means totalEstimate = 5+65; totalEstimate now = 70

document.estimate.cost.value = "$" + totalEstimate means it puts value $70 to the text box named "cost"

That's all. Hope this can help.

**AhmedScript** · 07-11-2012 04:23 AM

Thanks to both of u, it really helped me a lot.

ur clear explanation made me to grasp it easily, payukim. Thanks once again!

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