Problem with if statement

<!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 ro_div_b(form) {
ro=parseFloat(form.ro.value)
b=parseFloat(form.b.value)
c=ro/b
form.ans.value = c
}

function alfa(form) {
	form.ans3.value = a;error
}

var a = 10;
var error = "error";
if (c<5 && c>3)
{
	document.write(a);
	}
	else {
		document.write(error);
	}
</script>
</head>

<body>

<CENTER>
  
  <FORM name="formx">
  <table width="93" border="1">
  <tr>
    <td width="30">&#961;=</td>
    <td width="154"><input type=text size=4 value="" name="ro"></td>
  </tr>
  <tr>
    <td>b=</td>
    <td><input type=text size=4 value="" name="b"></td>
  </tr>
  <tr>
    <td>&#961;/b=</td>
    <td><input type "number" value=0 name="ans" size=9></td>
  </tr>
  <tr>
    <td colspan="2"><div align="center">
      
      <input type="button" value=" ok " onClick="ro_div_b(this.form);alfa(this.form)">
    </div></td>
    </tr>
  <tr>
    <td colspan="2">
      </div>
      <div align="center">
      <input type="type" "number" value="" name="ans3" size="9" />
      </div>
    </td>
  </tr>
  </table>
  
</FORM>

</CENTER>

</body>
</html>

problem is in function alfa…i am aware that there is no way this is going to work, but i need a solution

so if answer is between 3 and 5 it writes 10 and if it not it writes error

pls help

nice…it works…thanks!

function alfa(form) {
var c = parseFloat(form.ans.value);
form.ans3.value = (c<5 && c>3)? 10 : 'error';
}