Checking True

[mrgrammar]

I'm writing a program to check the answers of quizzes taken. Quizzes are true/false. The students' answers are stored in varchar as either 'True' or 'False' (without the quotes). The answer key stores the correct answers in another table as either 'True' or 'False' (without the quotes).

The correct answers are queried from the db. The student answers are queried from the db. The two are then compared and a point given if the student answer is correct.

if($correct_answer == $student_answer){$points = $points + 1;}

The issue is that at some point along the way, it stops working. Though both answer match (False == False), the program says they don't match. I'm wondering if it has to do with the actual answers themselves. Therefore:

Is this:

$answer = 'True';

the same as this?

$answer = TRUE;

[Weedpacket]

No: one assigns a string and the other assigns a boolean. To be compared one has to be cast to the same type as the other. font=monospaceTRUE[/font] is [font=monospace]"1"[/font] and font=monospace"True"[/font] is [font=monospace]true[/font], but then again font=monospace"False"[/font] is [font=monospace]true[/font] as well.

[sneakyimp]

Your question touches on PHP data types.

As Weedpacket says, this defines a string:

$answer = 'True';

but this defines a boolean value:

$answer = TRUE;

Note that PHP is a loosely typed language -- it performs automatic conversions between different data types depending on how you are using or comparing them.

You should get accustomed to experimenting with little snippets of code to learn how code works. [man]var_export[/man] and [man]var_dump[/man] are also very useful for inspecting the contents of variables to get a better idea of what's going on in your code.

[NogDog]

I'd strongly consider using 0/1 values in the DB (e.g. a TINYINT column type) and for the form values themselves for true/false, being just as portable yet more Boolean-like than strings. (You would then define a form element to have value="1" or value="0" while you can still display the text True or False as the element's label.) 0 and 1 play nicely with the "==" operator:

1 == true; // true
0 == false; // true

...whereas...

'true' == true; // true
'false' == false; // false

[sneakyimp]

To further complicate matters, your database might have a TINYINT column but your queries will return its contents as strings.

On my server:

	$db = new mysqli("localhost", "db_user", "****", "db_name");
	/* check connection */
	if ($db->connect_errno) {
    	printf("Connect failed: %s\n", $mysqli->connect_error);
    	exit;
	}

/* If we have to retrieve large amount of data we use MYSQLI_USE_RESULT */
if ($result = $db->query("SELECT * FROM my_table", MYSQLI_STORE_RESULT)) {
	$datarow = $result->fetch_array();
	echo "<pre>";
	var_dump($datarow);
	echo "/<pre>";

}

$result->close();

The output array, $datarow returns one record from the table. Note that is_active is defined as TINYINT(1) but returns as a string in my code. In fact, all of my columns are either TINYINT or INT -- not a single one is a string. Nevertheless, the output:

array(7) {
  ["id"]=>
  string(4) "123"
  ["userid"]=>
  string(6) "45678"
  ["customer_profile_id"]=>
  string(8) "01234567890"
  ["customer_payment_profile_id"]=>
  string(8) "01234567890"
  ["is_active"]=>
  string(1) "1"
}

[Weedpacket]

NogDog;11053033 wrote:

I'd strongly consider using 0/1 values in the DB (e.g. a TINYINT column type)

Better still of course is a proper boolean type (if the DB has such a thing).