Whats wrong here? Help

[asherinho]

I have a form with multiple select fields and text fields.Each select field is associated with a text field,the options of select fields carries the product name,id and unit saling price while the text fields takes the corresponding quantity.Here is my form

 

<form id="form1" name="form1" method="post" action="sale.php">
<select name="product_name1">
<option value="">Select...</option>
<option value="1" unit="3000">Cocacola</option>
<option value="2" unit="4000">Pepsi</option>
</select>
<select name="product_name2">
<option value="">Select...</option>
<option value="1" unit="3000">Cocacola</option>
<option value="2" unit="4000">Pepsi</option>
</select>
<input type="text" name="quantity1" size="20">
<input type="text" name="quantity2" size="20">
<input type="text" name="total_price" />
<input type="button" value="Calculate" onclick="cal()" />
<input type="submit" value="submit">
</form>

I want to calculate the total price by multiplying the unit sale price and quantity of each product then suming all of them,by using a javascript function call(),but it doesn't work.Below is the function

<script language="javascript">
function cal(){

var count= 3;
var i=1;
var total=0;
while(i<=count){
var num1=document.form1.product_name+i+.options.selectedIndex;
var pick1=document.form1.product_name+i+.selectedIndex;
  var total2=document.form1.product_name+i+.options(pick1).unit*document.form1.quantity_sold+i+.value;
  i=i+1;
  total=total+total2;
}
document.form1.total_price.value=total;
</script>

 

What is wrong with the code above?