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  1. #1
    Join Date
    May 2010
    Posts
    2

    calculation result display

    Hi,
    I am a beginner to coding javascript. I have spent many hours trying to get this calculation result to display in the form box in the browser window. I think the calculation is correct because it works when I use a calculator but it doesn't do anything as it is now coded. Do I use parseInt, or Math.round and do I display it by saying return payment;

    Any help would be greatly appreciated! Here's the code by cut and paste method:

    <html>
    <head>
    <title>Final exam 2</TITLE>
    <script>
    /* car payment calculation function coding here */
    <!--
    function calc(myform) {
    var interest = myform.rate.value / 100;
    var total = ((myform.price.value - myform.down.value) * (1 + myform.rate.value));
    var payment = myform.total.value / 60;{
    return payment;
    }

    </script>
    </head>
    <body bgcolor="#FFE4E1">
    <h1>Final Exam Car Payment Calculator(CPC)</h1>
    <p>
    </p><form name="myform" id="myform"><!--are the name and id required? I've seen examples of forms that are referenced in the script. The function is calling "myform" right?-->
    <table border="1">
    <tr>
    <td>Car Price:</td>
    <td><input type="text" value="0" name="price" /></td>

    </tr>
    <tr>
    <td>Interest rate:</td>
    <td><input type="text" value="5.5" name="rate" /></td>
    </tr>
    <tr>
    <td>Number of Years:</td>
    <td>5 years (60 months)
    </td>
    </tr>
    <tr>
    <td>Down Payment:</td>
    <td><input type="text" value="0" name="down" /></td>
    </tr>

    <tr>
    <td>Monthly Payment:</td>
    <td><input type="text" name="payment" onFocus="this.blur();" /></td><!--Why is this blur?-->
    </tr>
    </table>
    <p></p>
    <p>
    <input type="button" value="Calculate" onClick="return calc(this)" />
    <input type="reset" value="Reset" />
    </p></form>

    <hr />
    <h3>Question #2</h3>
    Write a JavaScript function - calc() with parameter/argument to calculate a car payment:
    <ul><li>interest = rate / 100</li>

    <li>total = ((price - down) * (1 + interest))</li>
    <li>payment = total / 60 </li>
    </ul>

    </body>
    </html>

    Thanks, in advance!!

  2. #2
    Join Date
    Mar 2010
    Posts
    2,803
    You have at least 1 syntax error and at least 1 logic error.

    The Firefox error console tells you exactly what the errors are.

    Using some basic Debugging 101 as described here http://www.webdeveloper.com/forum/sh...47#post1074647 you should be able to debug your code using either a debugger or alert() statements to check values of variables and your code logic.

  3. #3
    Join Date
    Oct 2006
    Posts
    939
    The math doesn't look right to me?

    HTML Code:
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
    	"http://www.w3.org/TR/html4/strict.dtd">
    <HTML>
    <HEAD><TITLE>Mo8-40am49</TITLE>
    <META http-equiv=Content-Type content="text/html; charset=UTF-8">
    <STYLE type=text/CSS>
    
    
    </STYLE>
    <SCRIPT type="text/javascript">
    function calc(myform) {
    	var f=document.forms[0].elements;				// identify forms and inputs by their index rather than name or id (personal prefrence)
    	var interest = f[1].value / 100; 				// alert(interest)
    	var total = ((f[0].value - f[2].value) * (1 + f[1].value)); 	// alert(total)
    	 f[3].value=(total / 60).toFixed(2);				// monthly payment
    	f[4].value=total
    }
    
    </SCRIPT>
    <META content="MSHTML 6.00.2900.2963" name=GENERATOR></HEAD>
    <BODY scroll="auto" bgcolor="#FFE4E1">
    <h1>Final Exam Car Payment Calculator(CPC)</h1>
    
    <form>
    <table border="1" style="text-align:right;border-collapse:collapse">
     <tr>
      <td>Car Price: <input value="1000" name="price" /></td></tr> <!--default type is text, leave off if text-->
     
    <tr>
      <td>Interest rate: <input value="5.5" name="rate" /></td></tr>
    <tr>
      <td>Number of Years: 5 years (60 months)  </td></tr>
    <tr>
      <td>Down Payment: <input value="90" name="down" /></td></tr>
    <tr>
      <td>Monthly Payment: <input name="payment" onFocus="this.blur();" /></td></tr><!--Why is this blur? A: this blur becasue you don't get to decide how much to pay per month-->
    <tr>
      <td>paid after 5 years <input></td></tr>
    </table>
     <p>
     <input type="button" value="Calculate" onClick="calc(this)" /><input type="reset" value="Reset" />
    </form>
    
    <hr />
    <h3>Question #2</h3>
    Write a JavaScript function - calc() with parameter/argument to calculate a car payment:
    <ul><li>interest = rate / 100</li>
    
    <li>total = ((price - down) * (1 + interest))</li>
    <li>payment = total / 60 </li>
    </ul>
    
    </BODY></HTML>

  4. #4
    Join Date
    May 2010
    Posts
    2
    Thanks so much for your detailed reply! I think it will really help me, both for this problem and with javascript overall. I am going to study your answer and work on this calculation this afternoon.

  5. #5
    Join Date
    Nov 2012
    Posts
    4
    This is just amazing indeed. I really like it and appreciate to you about this work.
    This is the way to expose your ideas...Keep it up...

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