带有复选框的HTML表单和使用PHP提交的数字类型？

Question

For learning purposes, I'm doing this website where user can select some items and the number of units he wants, let's say it's this simplest shopping app.

So, I read from database the existing items in catalog:

$queryResult=$mySQL->query("SELECT nombre, precio, id FROM productos");

Then I print the list of products:

    $queryResult=$mySQL->query("SELECT nombre, precio, id_producto FROM productos");
    echo "<form action=\"checkout.php\" method=\"POST\">";
    while($datos=$mySQL->fetch_array($queryResult))
    {   
        $nombre=$datos['nombre'];
        $id_producto=$datos['id_producto'];
        $precio=$datos['precio'];

        echo "<h1>$nombre</h1>";
        echo "<input type=\"checkbox\" name=\"$id_producto\" value=\"on\"> Cantidad: <input type=\"number\" name=\"$id_producto"."Number\""." min=\"1\" max=\"20\" step=\"1\" value=\"1\"><br>";
        echo "<h3>Precio: $precio</h3><br>";

    }

    echo "<br>";
    echo "<input type=\"submit\" class=\"button\" value=\"Comprar\">";
    echo "</form>";

They get as value the ones from $id_producto , in the case of the number type inputs I concatenate "Number" so they dont get the same name.

After submission, I'm trying to do something like:

foreach($_POST as $post_key => $post_value){     

    if ($post_value=="on") {
        $var1 = $_POST['.$post_key."Number".'];
    }
}

So if a checkbox was selected I check for its corresponding numeric value.

Is it OK to perform another $_POST['somevariable'] inside that loop?
How can I concatenate that argument inside the square brackets?

Answer 1

You don't need the single quotes, that's for when the key is a constant string. Since your key is an expression, just put that expression inside the brackets:

if ($post_value=="on") {
    $var1 = $_POST[$post_key."Number"];
}

A better way to do this is to post the inputs as arrays:

echo "<input type=\"checkbox\" name=\"producto[]\" value=\"$id_producto\"> Cantidad: <input type=\"number\" name=\"Number[$id_producto]\" min=\"1\" max=\"20\" step=\"1\" value=\"1\"><br>";

Then you can use the loop:

foreach ($_POST['producto'] as $post_value) {
    $var1 = $_POST['Number'][$post_value];
}