ArraysInPHP - //Problem 6. **Simple calculator

//Problem 6.    **Simple calculator
//Write a script that read two input number from user and choose operands. Put appropriate validation of input lines calculate and print //result on output line.
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
        <form action="SimpleCalculator.php" method="post">
        <input type="text" name="num1">
        <select name="operation">
            <option value="plus">+</option>
            <option value="minus">-</option>
            <option value="multiplication">*</option>
            <option value="divide">/</option>
        </select>
        <input type="text" name="num2">
        <input type="submit" value="enter!">
        </form>
    </body>
</html>
<?php
$num1 = $_POST['num1'];
$num2 = $_POST['num2'];
$operation=$_POST['operation'];
if ($operation=="plus") {
    echo $num1+$num2;
}
elseif ($operation=="minus") {
    echo $num1-$num2;
}
elseif ($operation=="multiplication") {
    echo $num1*$num2;
}
elseif ($operation=="divide") {
    echo $num1/$num2;
}
?>