如何在PHP

Question

如何總結textboxA總結文本框（從數據庫中值）和HTML文本框（手動輸入）（接到數據庫值）* textboxB（手動鍵入的值）

我想做= 價格*數量 - 盤=總

，其中從數據庫中生成價格的價值只想計算，

這裏是代碼

<?php 
$con = mysqli_connect('localhost', 'root', '', 'a.karat'); 
if(isset($_POST['product_id'])) 
{ 

    $prno=$_POST['prno']; 
    $i=1; 
    $sql = mysqli_query($con,"select * from detail_pr where prNo='$prno'"); 
    while ($r = mysqli_fetch_array($sql)) { 

     echo 

     '<tr> 
    <td><input type="checkbox" name="check[]" id="check'.$i.'" value="'.$i.'"></td> 
    <td><label for="productCode"></label> 
     <input type="text" name="productCode'.$i.'" id="productCode'.$i.'" readonly value="'.$r["productCode"].'" ></td> 
    <td><label for="productName"></label> 
     <input type="text" name="productName'.$i.'" id="productName'.$i.'" readonly value="'.$r["productName"].'"></td> 
    <td><label for="qty"></label> 
     <input type="text" name="price'.$i.'" id="price'.$i.'" readonly value="'.$r["qty"].'" ></td> 
    <td><input type="text" name="qty'.$i.'" id="qty'.$i.'" ></td> 
    <td><input type="text" name="disc'.$i.'" id="disc'.$i.'" ></td> 
    <td><input type="text" name="total'.$i.'" id="total'.$i.'" ></td> 
    </tr>'; 
    $i++; 
    } 
} 
?> 


<script type="text/javascript"> 
function calculate(id){ 
var quantity = document.getElementById('qty'+id).value; 
var price = document.getElementById('price'+id).value; 
var sum = parseInt(quantity,10)*parseInt(price,10); 
document.getElementById('total'+id).value = sum; 
} 
</script> 

我想知道怎麼做

價格*數量 - 盤=總

誰能幫助我？

感謝

Answer 1

<script type="text/javascript"> 
function calculate(id){ 
var quantity = document.getElementById('qty'+id).value; 
//alert("quantity: " + quantity); 
var price = document.getElementById('price'+id).value; 
//alert("price: " + price); 
var disc = document.getElementById('disc'+id).value; 
//alert("disc: " + disc); 
var sum = (parseInt(quantity,10)*parseInt(price,10)) - (parseInt(disc,10)); 
document.getElementById('total'+id).value = sum; 
} 
</script>