عدم کارکرد متد post!

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
    <script src="https://code.jquery.com/jquery-3.4.1.slim.min.js" integrity="sha384-J6qa4849blE2+poT4WnyKhv5vZF5SrPo0iEjwBvKU7imGFAV0wwj1yYfoRSJoZ+n" crossorigin="anonymous"></script>
    <script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js" integrity="sha384-wfSDF2E50Y2D1uUdj0O3uMBJnjuUD4Ih7YwaYd1iqfktj0Uod8GCExl3Og8ifwB6" crossorigin="anonymous"></script>
    <style>
        body{
            text-align: center;
        }
    </style>
</head>
<body>
<form method="$_POST">
  <div class="form-group">
    <label for="exampleInputEmail1">Number</label>
    <input type="text" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" name="number">
  </div>
  <button type="submit" class="btn btn-primary" name="submit">Submit</button>
</form>
<a href="<?php echo $_SERVER['SCRIPT_NAME']; ?>"."><button type="button" class="btn btn-danger">Reset</button></a>
<?php
if(isset($_POST["submit"])){
    if(!empty($_POST["number"])) {
        echo "<div class='alert alert-success'>".sqrt($_POST["number"])."</div>";
    }elseif(empty($_POST["number"])){
        echo "<div class='alert alert-danger'>Please fill the fields!</div>";
    }
}
?>
</body>
</html>

سلام استاد.خسته نباشید

من این کد را نوشتم ولی کار نمیکند!

مشکل چیست؟

باتشکر

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous"> <script src="https://code.jquery.com/jquery-3.4.1.slim.min.js" integrity="sha384-J6qa4849blE2+poT4WnyKhv5vZF5SrPo0iEjwBvKU7imGFAV0wwj1yYfoRSJoZ+n" crossorigin="anonymous"></script> <script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script> <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js" integrity="sha384-wfSDF2E50Y2D1uUdj0O3uMBJnjuUD4Ih7YwaYd1iqfktj0Uod8GCExl3Og8ifwB6" crossorigin="anonymous"></script> <style> body{ text-align: center; } </style> </head> <body> <form method="POST"> <div class="form-group"> <label for="exampleInputEmail1">Number</label> <input type="text" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" name="number"> </div> <button type="submit" class="btn btn-primary" name="submit">Submit</button> </form> <a href="<?php echo $_SERVER['SCRIPT_NAME']; ?>"."><button type="button" class="btn btn-danger">Reset</button></a> <?php if(isset($_POST["submit"])){ if(!empty($_POST["number"])) { echo "<div class='alert alert-success'>".sqrt($_POST["number"])."</div>"; }elseif(empty($_POST["number"])){ echo "<div class='alert alert-danger'>Please fill the fields!</div>"; } } ?> </body> </html>