Can't get AJAX to work, (very simple)

Hello.  I have two drop down boxes, upon the selection of an option in the second box, I would like this values sent to a PHP server using AJAX and printed in the appropriate div.  Why is my code not working?  Thank you.

Homepage

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>

<script type="text/javascript">
function showCars(car1, car2)
{
var xmlhttp;
if (car1.length==0)
  { 
  document.getElementById("txtHint").innerHTML="";
  return;
  }
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","gethint3.php?q="+car1 + "r&" + car2,true);
xmlhttp.send();
}
</script>


</head>

<body>
   <select name='one' id="one">
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
   </select>

   <select name="two" onchange="showCars(this, document.getElementById('one');">
    <option value="volvo" name="two">Volvo</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
   </select>
  
 <div id="txtHint"></div>

</body>
</html>

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<?php
$q=$_GET["q"];
echo $q;
$r=$_GET["r"];
echo $r;
?>

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Kiran SonawaneProject LeadCommented:
Try this

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<script src="http://code.jquery.com/jquery-1.7.2.js"></script>
<script type="text/javascript">



  $(document).ready(function(){
    
    
    $('#two').change(function(){
      var url1 = 'gethint3.php?q=' + $('#one').val() + '&r=' + $('#two').val();
      alert(url1);
       $.ajax({
       url: url1,
       dataType: 'text',
       data: {},
       success: function(data){
          $('#txtHint').html(data);
       }
       
     });
    })
      
  
  });

</script>


</head>

<body>
   <select name='one' id="one">
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
   </select>

   <select name="two" id="two">
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
   </select>
  
 <div id="txtHint"></div>

</body>
</html>

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Dave BaldwinFixer of ProblemsCommented:
Or try this:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>

<script type="text/javascript">
function showCars()
{
ndxcar1 = document.forms.formx.one.selectedIndex;
car1 = document.forms.formx.one.options[ndxcar1].value;
ndxcar2 = document.forms.formx.two.selectedIndex;
car2 = document.forms.formx.two.options[ndxcar2].value;
var xmlhttp;
if (car1.length==0)
  { 
  document.getElementById("txtHint").innerHTML="";
  return;
  }
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","gethint3.php?q="+car1 + "&r=" + car2,true);
xmlhttp.send();
}
</script>


</head>

<body>
<form action="" method="" name="formx">

   <select name='one' id="one">
	  <option>Select One</option>
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
   </select>

   <select name="two" id="two" onchange="showCars();">
	  <option>Select Two</option>
    <option value="volvo" name="two">Volvo</option>
    <option value="saab">Saab</option>
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
   </select>
  
</form>
 <div id="txtHint">---</div>

</body>
</html>

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<?php
$q=$_GET["q"];
echo $q." ";
$r=$_GET["r"];
echo $r;
?>

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NewWebDesignerAuthor Commented:
Dave Baldwin,  What is "formx?"  I have never seen that before.
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Dushyant SharmaCommented:
Two changes

xmlhttp.open("GET","gethint3.php?q="+car1 + "&r=" + car2,true);

and

<select name="two" onchange="showCars(this.options[this.selectedIndex].value, document.getElementById('one').options[document.getElementById('one').selectedIndex].value);">

your existing code is not working because there is a typo mistake in your html select code. You have not closed the showCars call in select element
Dave BaldwinFixer of ProblemsCommented:
"formx" is the name of the form.  I put the <select> statements in a <form> because it was an easy way (that I've done before) to get the value of the currently selected option.  There is probably another way but this is one I've done.
Dave BaldwinFixer of ProblemsCommented:
Here is an alternative way to get the currently selected value: http://www.w3schools.com/jsref/prop_select_selectedindex.asp   While the browser will send the selected value when you submit a form, it is a pain to get it in javascript on the same page.
4e4enCommented:
Also in your original code were error:
<select name="two" onchange="showCars(this, document.getElementById('one');">

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which should be replaced with
<select name="two" onchange="showCars(this, document.getElementById('one'));">

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