PHP Random Math Quiz Evaluation issue - php

Question

EDIT: When I print the $answer variable by itself it always returns the correct answer of the current question.
I am currently coding a PHP script that produces a simple, but completely random math quiz. How it works is that is gets two random numbers between 0-9 and a random operator from '-', '+', '*'. The user must enter into the text box the answer of the shown question. From here it's pretty straightforward to understand.
However, the issue I am having is that no matter what the user enters the only questions that are validated as correct are ones where the answer is 0.
Here is my code so far.
<?php
require 'functions.php';
$body = "";
$score = 0;
$count = 0;
if(isset($_POST['submit']))
{
$firstDigit = $_POST['lho'];
$secondDigit = $_POST['rho'];
$operator = $_POST['op'];
$userAnswer = $_POST['answer'];
$count = $_POST['count'];
$score = $_POST['score'];
$answer = evaluate($firstDigit, $secondDigit, $operator);
if($answer == $userAnswer)
{
$count++;
$score++;
$body .= "\n<h1>Congratulations!</h1>\n\n";
$body .= "$score out of $count";
}
else
{
$count++;
$body .= "\n<h1>Sorry!</h1>\n\n";
$body .= "$score out of $count";
}
}
header( 'Content-Type: text/html; charset=utf-8');
print("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n");
?>
<?php
include("./header.php");
?>
<h1>Math Quiz</h1> <br /> <br />
<?php
print $body;
?>
<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<h3><?php echo $firstDigit; ?> <?php echo $operator; ?> <?php echo $secondDigit; ?> = ?
<input type="text" name="answer" size="2" /></h3>
<p><input type="submit" name="submit" value="Try It!" />
<input type="hidden" name="lho" value="<?php echo randdigit(); ?>" />
<input type="hidden" name="rho" value="<?php echo randdigit(); ?>" />
<input type="hidden" name="op" value="<?php echo randop(); ?>" />
<input type="hidden" name="score" value="<?php echo $score++; ?>" />
<input type="hidden" name="count" value="<?php echo $count++; ?>" /></p>
</form>
<?php
include("./footer.php");
?>
My evaluate function is this:
function evaluate($d1, $d2, $op) {
switch($op) {
case '+' : // addition
$result = $d1 + $d2;
break;
case '-' : // subtraction
$result = $d1 - $d2;
break;
case '*' : // multiplication
$result = $d1 * $d2;
break;
default : // Unidentified, return safe value
$result = 0;
}
return $result;
}
Here is the randop() function and the randdigit() function:
/* Return a number in the range 0-9 inclusive
*/
function randdigit() {
return mt_rand(0,9);
} // end functionranddigit()
function randop(){
$ops = array('+', '-', '*');
// pick a random index between zero and highest index in array.
$randnum = mt_rand(0,sizeof($ops)-1);
return $ops[$randnum]; // Use the index to pick the operator
}

Answer 1

First on the 48th line :
<h3><?php echo $firstDigit; ?> <?php echo $operator; ?> <?php echo $secondDigit; ?> = ?
When you first load the form and until it has been submitted once,
$firstDigit, $operator, $secondDigit
Aren't set.
Then, this line wich is the equation to solve is filled with the old equation that needed to be solved AND your hidden fields are filled with new numbers, invisible to the user using randdigit() and randop().
<input type="hidden" name="lho" value="<?php echo randdigit(); ?>" />
<input type="hidden" name="rho" value="<?php echo randdigit(); ?>" />
<input type="hidden" name="op" value="<?php echo randop(); ?>" />
Here is the code that works well for me :
<?php
require 'functions.php';
$body = "";
$score = 0;
$count = 0;
$newFdigit = randdigit();
$newSdigit = randdigit();
$newOperator = randop();
if(isset($_POST['submit']))
{
$firstDigit = $_POST['lho'];
$secondDigit = $_POST['rho'];
$operator = $_POST['op'];
$userAnswer = $_POST['answer'];
$count = $_POST['count'];
$score = $_POST['score'];
$answer = evaluate($firstDigit, $secondDigit, $operator);
if($answer == $userAnswer)
{
$count++;
$score++;
$body .= "\n<h1>Congratulations!</h1>\n\n";
$body .= "$score out of $count";
}
else
{
$count++;
$body .= "\n<h1>Sorry!</h1>\n\n";
$body .= "$score out of $count";
}
}
header( 'Content-Type: text/html; charset=utf-8');
print("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n");
?>
<h1>Math Quiz</h1> <br /> <br />
<?php
print $body;
?>
<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<h3><?php echo $newFdigit; ?> <?php echo $newOperator; ?> <?php echo $newSdigit; ?> = ?
<input type="text" name="answer" size="2" /></h3>
<p><input type="submit" name="submit" value="Try It!" />
<input type="hidden" name="lho" value="<?php echo $newFdigit ?>" />
<input type="hidden" name="rho" value="<?php echo $newSdigit; ?>" />
<input type="hidden" name="op" value="<?php echo $newOperator; ?>" />
<input type="hidden" name="score" value="<?php echo $score++; ?>" />
<input type="hidden" name="count" value="<?php echo $count++; ?>" /></p>
</form>