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Thread: Calculating Percentage in a form

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  1. #1
    Join Date
    Oct 2008
    Beautiful BC

    Calculating Percentage in a form

    Hi there and thanks in advance for any assistance.
    I am writing a form and doing a bunch of calculations one of which is a percentage based on the value selected. I am returning a correct result for two of the values but for the other two I am not.
    Clearly I am missing something and maybe not testing for it but as I am clueless I can't think of what.
    The 'discount' value is what I am looking for. It should return as 0 for values of 1 but it is doing the math as though it is multiplying by 1. And again for the value of 6 it should be 10% but is taking the value as 4.6 or something.

    Code is below I've included all of it (sorry) for better ease of understanding the math that is happening:
    HTML Code:
    <form id="form1" action="" method="get">
    	<label for="Type">Type of Storage:</label>
    	<select id="Type" name="type">
    		<option name="Heated Storage" value="60">Heated - $60/month</option>
    		<option name="Unheated Storage" value="50">Unheated - $50/month</option>
    		<option name="Offsite Storage" value="40">Offsite - $40/month</option>
    	<label for="Length">How long you need storage:</label>					
    	<select id="Length" name="length">
    		<option name="Don't know" value="1">Unsure (month to month)</option>
    		<option name="One month" value="1">One month </option>
    		<option name="3 months" value="3">3 months (5% pre-payment discount)</option>
    		<option name="6 months" value="6">6 months (10% pre-payment discount)</option>
    		<option name="one year" value="12">One year (15% pre-payment discount)</option>
    	<label for="Gobox">Number of Goboxes:</label>					
    		<select id="Gobox" name="gobox">
    			<option value="1">1 - $70 delivery fee</option>
    			<option value="2">2 - $100 delivery fee</option>
    			<option value="3">3 - $130 delivery fee</option>
    			<option value="4">4 - $160 delivery fee</option>
    			<option value="5">5 - $190 delivery fee</option>
    			<option value="6">6 - $220 delivery fee</option>
    			<option value="7">7 - $250 delivery fee</option>			
    			<option value="8">8 - $280 delivery fee</option>
    			<option value="9">9 - $310 delivery fee</option>
    			<option value="10">10 - $340 delivery fee</option>
    		<label for="delivery">Delivery:</label>
    		<input type="text" id="delivery" size="10" maxlength="10" readonly="readonly" value="0" />
    	<br />
    		<label for="storageCosts">Storage Costs:</label>
    		<input type="text" id="storageFees" size="10" maxlength="10" readonly="readonly" value="0" />
    	<br />
    	<label for="discount">Discount:</label>
    		<input type="text" id="discount" size="10" maxlength="10" readonly="readonly" value="0" />
    	<br />
    		<label for="taxes">Taxes:</label>
    		<input type="text" id="roundedTaxes" size="10" maxlength="10" readonly="readonly" value="0" />
    	<br />
    		<label for="total">Final Total:</label>
    		<input type="text" id="finalTotal" size="10" maxlength="10" readonly="readonly" value="0" />
    	<p align="right" ><input type="button" id="submit" value="Get an Esitmate" onclick="processForm()" />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>
    <script type="text/javascript">
    function roundNumber(num, dec) {
    	var result = Math.round(num*Math.pow(100,dec))/Math.pow(100,dec);
    	return result;
    function processForm() {
    	//get form variables
    	var theType = form1.type.options[form1.type.selectedIndex].value;
    	var theLength = form1.length.options[form1.length.selectedIndex].value;
    	var theGoBox = form1.gobox.options[form1.gobox.selectedIndex].value;
    	//set tax rate
    	var theTaxes = 0.07;
    	//set shipping rate
    	var theShipping = 30.00;
    	//variable for order total
    	var orderTotal = 0.00;
    	//the display box
    	var deliveryBox = document.getElementById( "delivery" );
    	var storageBox = document.getElementById( "storageFees" );
    	var discountBox = document.getElementById( "discount" );
    	var taxesBox = document.getElementById( "roundedTaxes" );
    	var totalBox = document.getElementById( "finalTotal" );
    	//Calculate Delivery
    	delivery = (theGoBox * theShipping) + 40;	
    		//Calculate Storage Costs
    	storageFees = ((theType * theGoBox)* theLength);
    	//Calculate prepayment Discount
    	if (theLength = 3) {
    		//multiply storage costs by 5% 
    		discount = storageFees *(5/100);
    		else if (theLength = 6) {
    		//multiply storage costs by 10% 
    		discount = storageFees *(10/100);
    		else if (theLength = 12) {
    		//multiply storage costs by 15% 
    		discount = storageFees *(15/100);
    		else {
    			discount = 0;
    	//Calculate Taxes
    	taxes = (storageFees + delivery) * theTaxes;
    	var roundedTaxes = roundNumber(taxes,2);
    	//figure final total
    	finalTotal = delivery + storageFees + roundedTaxes;
    	//output to text boxes
    	deliveryBox.value = "$" + delivery;
    	storageBox.value = "$" + storageFees;
    	discountBox.value = "$" + discount;
    	taxesBox.value = "$" + roundedTaxes;
    	totalBox.value = "$" + finalTotal;

  2. #2
    Join Date
    Mar 2010
    Had a quick look through your code. I haven't checked the logic but you have a syntax error at

    if (theLength = 3) {
    and in similar lines elsewhere in your code.

    Fix that and hopefully your form will process correctly.

  3. #3
    Join Date
    Jan 2009
    To be more specific you have an assignment operator (=) instead of a comparison operator (==). This same problem occurs in several places.

    I haven't checked the logic but you have a syntax error at
    Technically this is not a syntax error. It is a logical error. A syntax error would prevent execution of the code. A logical error doesn't do what was intended.

  4. #4
    Join Date
    Oct 2008
    Beautiful BC
    Thank-you criterion9 & tirna I actually dreamed that exact thing last night...worked like a charm! Much obliged.

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