I just cant get my head around setting form value

[ICEcoffee]

Hi all

I've spent so much time trying to set these form values, it's getting silly not to mention frustrating. Here is what I am trying to do, (see code below):

A form is presented with a table partially completed, taking values stored in a database. The field I am interested in is "Price". Whether the user chages this value or not is not the issue (I think). What I'm tring to do is to set 2 hidden fields with values based on the value of "price".

I was told on a previous thread, the "value" option within the <input> tag, is text only and cant contain a call to a funtion. so how do I set the values of the fields called Vat and PriceMinusVat? I want do do some math on the Value of "Price" to get the values for the other 2 fields.

Please help whilst I still have hair.

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<input name="Price" type="text" id="price" style="height:20px; font-family:Arial,Tahoma; font-size:11px " value="<?php echo $row_RSparts['Price']; ?>" size="10" maxlength="10">
<td height="18" colspan="2"><input type="submit" name="Submit4" value="Submit">
<input name="Callid" type="hidden" id="Callid43" value="<?php echo $HTTP_GET_VARS['Callid']; ?>">
<input name="ID" type="hidden" id="ID"> <br> </td>
<td height="18"><input name="PartPageNum" type="hidden" id="PartPageNum" value="<?php echo $row_RSpartpagenum['PageNum'] +1; ?>">
<input name="VAT" type="hidden" id="VAT" value="">
<input name="PriceMinusVAT" type="hidden" id="PriceMinusVAT" value=""></td>

=======================================

[Kor]

[/quote]
I want do do some math on the Value of "Price" to get the values for the other 2 fields.
[/quote]

The text value is a string not a number (nomatter if it is initially set or input by user). Thus to operate math with these values you have to parse them into integer using parseInt() or Number() methods.

[ICEcoffee]

I don't understand, what do you mean and will this solve the problem?:mad:

[Fang]

<input name="Price" type="text" id="price" value="<?php echo $row_RSparts['Price']; ?>" size="10" maxlength="10" onchange="DoSomeMaths();">

[Kor]

Fang is also right:

1. you need an event handler to fire a function, thus he suggest "onchange"

2. The input's value is a string. Thus if you take it as a variable

var v= document.forms[0].inputname.value, where let's say user input : "7"

and try, for instance, to add a number

var sum=v+3;

The result will be 73 (concatenate two strings) not 10, as you intended to do as a math operator.

Thus you need something like

var v= parseInt(forms[0].inputname.value)

to be sure that your value will be treated as number, not as string