为什么所有4个.php函数都显示为提交?

Started playing with .php a couple weeks ago and found this problem in a book. I have 4 different buttons that will call different functions respectively but currently all 4 of my functions are called when I click individual buttons? Need a little help understanding this one. Everything is working fine except the call. With each button submit a different function should be called. I have the html separate from the php code. What I'm looking at is click a button and the function is called. Currently it is calling all functions at the same time.

HTML:

    <?php 
if (isset($_POST['Sequence1'])) {
    echo Sequence1(); }
    else if (isset($_POST['Sequence2'])) {
        echo Sequence2(); }
        else if (isset($_POST['Sequence3'])) {
            echo Sequence3(); }
            else if (isset($_POST['Sequence4'])) {
                echo Sequence4(); }
?>
<!doctype html>
<html>
<head>
<title>Sequence Test</title>
<link rel="stylesheet" type="text/css" href="q2.css">
</head>
<body>
<form action="q2_process.php" method="post">
<div class="header">
<header><h1>Numeric Sequence Tester</h1></header>
</div>
<div class="prompt">
<h2>Click on a button below to see the sequence</h2>
</div>
<div class="button1">
    <p><button type="submit" formmethod="post" name="Sequence1" value="Sequence1" class= "buttons">Sequence 10 - 2n</button></p>
    </div>
    <div class="button2">
    <p><button type="submit" formmethod="post" name="Sequence2" value="Sequence2" class="buttons">Sequence 4n + 3</button></p>
    </div>
    <div class="button3">
    <p><button type="submit" formmethod="post" name="Sequence3" value="Sequence3" class="buttons">Sequence n*n - 2</button></p>
    </div>
    <div class="button4">
    <p><button type="submit" formmethod="post" name="Sequence4" value="Sequence4" class="buttons">Sequence ar^n; when a-4 r=3</button></p>
</div>

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

PHP Functions:

    <?php
function Sequence1() {
    $num = 0;
    $result = 0;
    for($i = 0; $i < 9; $i++) {
        $num++;
        $num1 = (2 * $num);
        $result = 10 - $num1;
        echo "When n=${num};   10-2n = 10-2x $num1 = 10 - $num1 = $result  <br>"; }} ?>
<?php function Sequence2() {
    $num = 0;
    $result = 0;
    for($i = 0; $i < 9; $i++) {
        $num++;
        $num1 = (4 * $num);
        $result = $num1 + 3;
        echo "When n=${num};    4n+3 = 4 x $num + 3 = $num1 + 3 = $result <br>"; }}; ?>

<?php function Sequence3() {
    $num = 0;
    $result = 0;
    for($i = 0; $i < 9; $i++) {
        $num++;
        $num1 = ($num* $num);
        $result = $num1 - 2;
        echo "When n=${num};    n*n-2 = $num x $num - 2 = $num1 - 2 = $result <br>"; }}; ?>

<?php function Sequence4() {
    $num = 0;
    $result = 0;    
    for($i = 0; $i < 9; $i++) { 
        $a = 3;
        $r = 2; 
        $num++;
        $num1 = $a * pow($r, $num -1);
        $result = $num1 * 2;
        echo "When n=${num};    $num1 x 2 = $result <br>"; }} ?>

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Sequence Tester</title>
<link rel="stylesheet" type="text/css" href="q2.css">
</head>
<body>
<div class="header">
<header><h1>Sequence Tester</h1></header>
</div>
<!--Create divs to hold each button click-->
<div class="seq1">
<h3>You selected button 1</h3>
<p><?php echo Sequence1(); ?></p>
</div>

<div class="seq2">
<h3>You selected button 2</h3>
<p><?php echo Sequence2(); ?></p>
</div>

<div class="seq3">
<h3>You selected button 3</h3>
<p><?php Sequence3(); ?></p>
</div>
<div class="seq4">
<h3>You selected button 4</h3>
<p><?php Sequence4(); ?></p>
</div>

<div class="home">
<a href="q2_index.html">Back to Homepage</a>
</div>

</body>
</html>

You are calling each function here:

<div class="seq1">
<h3>You selected button 1</h3>
<p><?php echo Sequence1(); ?></p>
</div>

<div class="seq2">
<h3>You selected button 2</h3>
<p><?php echo Sequence2(); ?></p>
</div>

<div class="seq3">
<h3>You selected button 3</h3>
<p><?php Sequence3(); ?></p>
</div>
<div class="seq4">
<h3>You selected button 4</h3>
<p><?php Sequence4(); ?></p>
</div>

And that's why it appears that all buttons are submitted.

Edited to answer your second question as to why the function is being output on top of the DOM:

The output on top of the DOM is coming because you are calling your php functions here:

if (!empty($_POST['Sequence1'])) {
    $v = "button 1";
    Sequence1(); }
else if (isset($_POST['Sequence2'])) {
    $v = "button 2";
    Sequence2();  }
else if (isset($_POST['Sequence3'])) {
    $v = "button 3";
    Sequence3(); }
else if (isset($_POST['Sequence4'])) {
    $v = "button 4";
    Sequence4(); ; }

Since each function is defined by you to 'echo' results instead of 'returning' them to a variable (see your function description), it is outputted near the top of the page when you call it in the if/else loop above.

Edited I made some changes to your function calls to 'return' the values instead and then display them in the correct div. Try this:

    <?php
$v = '';
$j = '';
if (!empty($_POST['Sequence1'])) {
    $v = "button 1";
    $j = Sequence1(); }
else if (isset($_POST['Sequence2'])) {
    $v = "button 2";
    $j = Sequence2();  }
else if (isset($_POST['Sequence3'])) {
    $v = "button 3";
    $j = Sequence3(); }
else if (isset($_POST['Sequence4'])) {
    $v = "button 4";
    $j = Sequence4(); }
?>
<!doctype html>
<html>
<head>
    <title>Sequence Test</title>
    <link rel="stylesheet" type="text/css" href="q2.css">
</head>
<body>
<form action="" method="post">
    <div class="header">
        <header><h1>Numeric Sequence Tester</h1></header>
    </div>
    <div class="prompt">
        <h2>Click on a button below to see the sequence</h2>
    </div>
    <div class="button1">
        <p><button type="submit" formmethod="post" name="Sequence1" value="Sequence1" class= "buttons">Sequence 10 - 2n</button></p>
    </div>
    <div class="button2">
        <p><button type="submit" formmethod="post" name="Sequence2" value="Sequence2" class="buttons">Sequence 4n + 3</button></p>
    </div>
    <div class="button3">
        <p><button type="submit" formmethod="post" name="Sequence3" value="Sequence3" class="buttons">Sequence n*n - 2</button></p>
    </div>
    <div class="button4">
        <p><button type="submit" formmethod="post" name="Sequence4" value="Sequence4" class="buttons">Sequence ar^n; when a-4 r=3</button></p>
    </div>

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

PHP Functions:

<?php
function Sequence1()
{
    $output = "";
    $num = 0;
    $result = 0;
    for ($i = 0; $i < 9; $i++) {
        $num++;
        $num1 = (2 * $num);
        $result = 10 - $num1;
        $output .= "When n=${num};   10-2n = 10-2x $num1 = 10 - $num1 = $result  <br>";
    }
    return $output;
}

function Sequence2()
{
    $output = "";
    $num = 0;
    $result = 0;
    for ($i = 0; $i < 9; $i++) {
        $num++;
        $num1 = (4 * $num);
        $result = $num1 + 3;
        $output .= "When n=${num};    4n+3 = 4 x $num + 3 = $num1 + 3 = $result <br>";
    }
    return $output;
}

function Sequence3()
{
    $output = "";
    $num = 0;
    $result = 0;
    for ($i = 0; $i < 9; $i++) {
        $num++;
        $num1 = ($num * $num);
        $result = $num1 - 2;
        $output .= "When n=${num};    n*n-2 = $num x $num - 2 = $num1 - 2 = $result <br>";
    }
    return $output;
}

function Sequence4() {
    $output = "";
    $num = 0;
    $result = 0;
    for($i = 0; $i < 9; $i++) {
        $a = 3;
        $r = 2;
        $num++;
        $num1 = $a * pow($r, $num -1);
        $result = $num1 * 2;
        $output .= "When n=${num};    $num1 x 2 = $result <br>";
    }
    return $output;
}

?>

<!doctype html>
<html>
<head>
    <meta charset="utf-8">
    <title>Sequence Tester</title>
    <link rel="stylesheet" type="text/css" href="q2.css">
</head>
<body>
<div class="header">
    <header><h1>Sequence Tester</h1></header>
</div>
<!--Create divs to hold each button click-->
<div class="seq_result">
    <h3>You selected <?php echo $v; ?></h3>
    <p><?php echo $j; ?></p>
</div>

<div class="home">
    <a href="q2_index.html">Back to Homepage</a>
</div>

</body>
</html>