[RESOLVED] Simple Grade Output code help

gsteak

Hi guys. I need help with a simple php assignment. I feel as if I'm almost there, but I'm just not able to get the correct output. I'm wondering if you could possibly clue me in on what I'm doing incorrectly?

<?php
if(!isset($_POST['submit'])) {
}
else {

if (is_numeric($_POST['grade1']) && is_numeric($_POST['grade2']) && is_numeric($_POST['grade3']) ) {
	$grade1=$_POST['grade1'];
	$grade2=$_POST['grade2'];
	$grade3=$_POST['grade3'];
}
else{
echo "Entries must be numeric.";
}

$total=($grade1 + $grade2 + $grade3) / 3; 

if ($total >= 90 && $total <=100) {
echo "<h1>Final Grade: A</h1>";
}
elseif ($total >= 80 && $total <= 89.9999) { 
echo "<h2>Final Grade: B</h2>";
}
elseif ($total >= 70 && $total <=79.9999) { 
echo "<h3>Final Grade: C</h3>";
}
elseif ($total >= 60 && $total <=69.9999) { 
echo "<h4>Final Grade: D</h4>";
}
elseif ($total >= 50 && $total >=0) { 
echo "<h5 color='red'>Final Grade: F<br /> Please study harder next time.</h5>";
}
}
?>
<html>
<body>
<form action="$SERVER['PHP_SELF']" method="post">
Grade 1:
<input type="text" name="grade1" size="3" /><br />
Grade 2:
<input type="text" name="grade2" size="3" /><br />
Grade 3:
<input type="text" name="grade3" size="3" /><br />
<input type="submit" name="submit" value="Submit" />
</form>
</body>
</html>

johanafm

First off, you should never use equality comparison on floats since they can't be guaranteed to be stored without loss of precision, and such errors can be very hard to track down.
Also, you have gaps in your comparisons. For example, what happens if a total grade becomes 89.99991?
As such, you'd be better off with

if ($total >= 90 && $total <= 100) {

}
# here everything up to exactly 90 (exclusive) is included, and since the integer 90 can be
# stored without loss of precision, this comparison is safe
elseif ($total >= 80 && $total < 90)

Then you have a huge gap between the last two comparisons, i.e. when $total is between 50 and 60.

Next up, you have an error in the last comparison, and I'd recommend restructuring your comparisons on the form LOW_NUM < $var && $var < HIGH_NUM so that it's easier to see that $var should be between the low and high bounding numbers

# suddenly it becomes clear that something isn't right here
if (50 <= $total && 0 <= $total)

# should be
if (0 <= $total && $total < 50)

# and taking the previous comment about the gap between 50 and 60 into account
if (0 <= $total && $total < 60)

Also, you could write less code if you structure your conditionals from lowest to highest

if ($total < 60) {
	# F
}
elseif ($total < 70) {
	# D
}
// ...
elseif ($total >= 90) {
	# A
}

gsteak

Wow. Thank you so much. I knew I was close, but I had no idea that I had completely overlooked that my numbers didn't make sense. Everything runs perfectly when I make the form action = thefile.php. However, when I equate the action to "$SERVER['PHP_SELF']" I get an error that says:

Not Found

The requested URL /Lab1/$SERVER['PHP_SELF'] was not found on this server.

I remember learning in class that I was supposed to use the PHP_SELF command when I want forms and php on the same page, but I may have completely misunderstood.

What can I do to remedy this?

johanafm

Personally, when I want to post back to the same script, I prefer using and empty action attribute

<form action="" method="post">

Your problem however is a missing underscore: $SERVER is not the same as $_SERVER.

Pikachu2000

Using $_SERVER['PHP_SELF'] as a form action is a known XSS vulnerability, and as such should be avoided. As johanafm suggested, use action="" or specify the script explicitly.

gsteak

Thank you very much for the input. I've shared your information with my class.