I have created a calculator using `if` statement in `PHP` and I was able to get the output i needed.
I am stuck with switch case. I'm not getting the output I want.

This is my code:

```
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Untitled Document</title>
<?php 
$num1 = "";
$num2 = "";
$calc = "";

if (isset($_POST['submit']))
{

 $num1 = $_POST['n1'];
 $num2 = $_POST['n2'];

function calculate($num1,$num2,$calc){
    switch ($_POST['submit']) {
        case 'addition':
            $calc = $n1 + $n2;
            break;

        case 'sub':
            $calc = $n1 - $n2;
            break;
    }

}
}
?>
</head>

<body>

    <form action="" method="post">
        NO 1 : <input  name='n1' value="<?php echo $num1;?>">
        <br><br>
        NO 2: <input  name='n2' value="<?php echo $num2?>"><br><br>
        total: <input type="res" value="<?php echo $calc;?>"><br><br>
        <input type="submit" name="submit" value="+">
        <input type="submit" name="submit" value="-">

    </form>
</body>
</html>

```