Sum Values From Form Fields

programming web dev
1

Hello,
I am working on a script, but I’m really not an expert. Any help will be highly appreciated.
Description:
I have items - some have option for adding an amount and some not (because they can be only 1).
I need when the checkboxes are clicked (choosing an item) the total to be displayed in the text field at the bottom.
the single items work fine, but when i choose the one that can be added amount, it deletes the total from the first ones.
Below is the script so you can see what I’m trying to explain:



<html><head>
<script type="text/JavaScript"><!-- 

        var Cost;
        var Amount = 0;

function getNumber() {	
		Amount = document.orderform.EVT_01.value;
		}
function tally()        {
        Cost = 0;
        if (document.orderform.Item1.checked) { Cost = Cost + 40; }
        if (document.orderform.Item2.checked) { Cost = Cost + 30; }
        if (document.orderform.Item3.checked) { Cost = 100 * Amount; }
		
Cost = dollar(Cost);
document.orderform.Total.value = "$" + Cost;
        }

function dollar (amount)
{
        amount = parseInt(amount * 100);
        amount = parseFloat(amount/100);
        if (((amount) == Math.floor(amount)) && ((amount - Math.floor (amount)) == 0))
        {
                amount = amount + ".00"
                return amount;
        }
        if ( ((amount * 10) - Math.floor(amount * 10)) == 0)
        {
                amount = amount + "0";
                return amount;
        }
        if ( ((amount * 100) - Math.floor(amount * 100)) == 0)
        {
                amount = amount;
                return amount;
        }
        return amount;
}

//--></script>
</head>
<body><form name="orderform">
<table width="500" border="0" cellspacing="1" cellpadding="1">
<tr><td width="167"><input type="checkbox" name="Item1" value="Item1_chosen" onClick="tally()" />AAA</td>
<td width="51">$40</td>
<td width="109">&nbsp;</td></tr>
<tr><td><input type="checkbox" name="Item2" value="Item2_chosen" onClick="tally()" />BBB</td>
<td>$30</td>
<td>&nbsp;</td></tr>
<tr><td colspan="3">&nbsp;</td></tr>
<tr><td><input type="checkbox" name="Item3" value="Item3_chosen" onClick="tally()" /><span class="EventPrice"><a href="#" title=" CCC " 

target="_blank">CCC</a></span></td>
<td><span class="EventPrice">$100</span></td>
	
<td>Amount:<input name="EVT_01" type="text" id="EVT_01" value="0" size="3" maxlength="3" onChange="getNumber()" /></td></tr>
<tr>
<td colspan="3">&nbsp;</td></tr>
<tr><td>Total:<input name="Total" type="text" value="$0" size="7" readonly="readonly"></td>
<td colspan="2">&nbsp;</td></tr>
</table></form></body></html>

Thanks in advance for your help!