<?php

session_start();

$op_arr = ['+','-','*'];

$no1 = rand(10,20);

$op = $op_arr[rand(0,2)];

$no2 = rand(1,9);

$sum = "{$no1}"."{$op}"."{$no2}";

$result = eval("return $sum;");

$captcha = $sum;

$_SESSION['result']= $result;

?>

<!DOCTYPE html>

<html lang="en">

<head>

<meta charset="UTF-8">

<meta name="viewport" content="width=device-width, initial-scale=1.0">

<title>Text captch example</title>

</head>

<body>

<h1><center>TEXT CAPTCHA</center></h1>

<hr>

<form action="mathcode.php" method="post">

<p>Enter the email : <input type="text" name="email"/></p>

<p>Solve the expression : <strike><mark><?php echo $captcha; ?> =</mark></strike>  <br>

<input type="text" name="captcha"  /></p>

<p><input type="submit" name="submit"/></p>

</form>

</body>

</html>


============mathcode.php===========


<?php

$email = $_POST['email'];

$captcha = $_POST['captcha'];

session_start();

$sess_capcha = $_SESSION['result'];

echo $sess_capcha;

?>