How to pass form from a page with header as example.com?a=100?

Question

There is a form in adminhome.php?action=addbook named addbook

<form name="addbook" action="adminhome.php?action=addbook" method="get" onsubmit="validatenumber();">
     Code:<br/><input type="text" name="code" ><br/>
     Class:<br/><input type="number" name="class" id="class1"><br/>
     title:<br/><input type="text" name="title"><br/>
     price:<br/><input type="number" name="price" id="price"><br/>
     quantity:<br/><input type="number" name="quantity" id="quantity"><br/>
     category:<br/><input type="text" name="category"><br/>
     <input type="submit" value="submit"><br/>
 </form>

What should be the correct action in the form action attribute given below?

action="adminhome.php?action=addbook&addbook.php" 

Actually when I submit form it is not getting validated.

<script language="javascript">
    function validatenumber(){
        var class1=document.getElementByName("class")[0];
        if(parseInt(class1.value, 10) < 0){
            alert("Please enter positive integer");
            return false;
        }
    }
</script>

Answer 1

 <form name="addbook" action="adminhome.php" method="get" onsubmit="validatenumber();"> Code:<br/><input type="text" name="code" ><br/> Class:<br/><input type="number" name="class" id="class1"><br/> title:<br/><input type="text" name="title"><br/> price:<br/><input type="number" name="price" id="price"><br/> quantity:<br/><input type="number" name="quantity" id="quantity"><br/> category:<br/><input type="text" name="category"><br/> <input type="hidden" name="action" value="addbook"> <input type="submit" value="submit"><br/> </form> 

That would make all of the form inputs and the action available in the $_GET[] global in file adminhome.php