My first PHP coding attempt...not going well...

jb3

I am an extreme newbie to PHP, as of a few hours actually and have been going through some tutorials trying to put together a little calculating app and am wondering if anyone here could help me to get the $sum variable to calculate how I have it written in? I have been researching, but I think I just do not have enough experience to know what answer I am looking for. I thought I had the syntax correct...but it's not working for me any way I try to plug it in.

Thanks in advance for any assistance.

<html>


<head>
<title>Calculator</title>
</head>
<body>

<h2>Calculator</h2>

<form action = "<?php echo $_SERVER["PHP_SELF"]; ?>"
method = "GET">
Enter the price of item:
<input type = "text" name = "pog_score" size=5>
<br />
Enter the amount of gold you are buying:
<input type = "text" name = "amount_score" size=5>
<br />
Enter the price the person is asking:
<input type = "text" name = "asking_score" size=5>
<br />
<input type = "submit" name = "Calculate Score"/>
</form>

<?php
$item_price = $_GET['pog_score'];
$amount_price = $_GET['amount_score'];
$asking_price = $_GET['asking_score'];
$total_price = '$asking_price * $value_price';
$sum= '$asking_price / $total_price * 1';

{ 
Echo " <b>You are paying a " . ($sum) ." premium on your purchase<br></b>";
Echo "<b>Value:</b> " . floor($item_price * $amount_price) ." Dollars <br>";


}
?>

NogDog

You do not want those single-quotes around your arithmetic expressions on these lines:

$total_price = '$asking_price * $value_price';
$sum= '$asking_price / $total_price * 1';

Also there's no need I can see for the parentheses around $sum in the next line, nor for that matter the curly braces around those last couple lines of code.

jb3

Thanks for the suggestions, I put them in but that line still doesn't do the math. Maybe I am doing something wrong with my sequence, you can do math on variables right? The php with changes as I go is active here: http://www.johnburgreen.com/gold/

jb3

$sum= $asking_price / $total_price * 1;

...this is a correct way to divide one variable by another variable and then multiply that by 1 right? Seems so easy, but this is where my hangup is....

laserlight

jb3 wrote:
this is a correct way to divide one variable by another variable and then multiply that by 1 right?

Yes, though multiplying by 1 is rather... silly, unless that happens to be the value of a variable.

jb3

The PHP file, when I use it still does not function....it does not calculate the math for $sum.

$total_price = $asking_price * $value_price;
$sum= $asking_price / $total_price;

Could it be that $sum is referencing a variable that is performing a calculation of its own? Not sure if that is a no no....

Weedpacket

The only hangup with the division is that it doesn't make sense if $total_price happens to be zero. It will be if this page is loaded without any GET values supplied (because then the "amount" and "asking" scores/prices would be zero).

Division by zero results in a "Not A Number" value, and also triggers a warning.

jb3

Ok, I may have to rethink this....I have everything set up in Excel fine, but trying to get my thoughts on the math carried over to PHP is where I am losing my mind maybe. The math should be as follows:

Example: Coin cost is $100.00 + $5.00 a/h fee = $117.00 (user input)

American Gold Eagle = 1/10th oz gold (user input)

Take your live gold spot price (which is now $845.30) and multiply your gold weight times your spot price. (user input)

$845.30 X .10 (1/10th oz) = $84.53 Your $84.53 is your gold content value inside the coin. This is how much $ value you have in gold according to golds spot price. If golds spot price was $800.00, you do the same multiplication times $800.00. .10X $800 = $80.00

$117.00 - $84.53 = $32.47

Your $32.47 is your premium paid including your s/h fees.

Divide your premium cost by your total cost gives your percentage premium paid over gold content.

$32.53 / $117.00 = .2775% premium or 28% premium.

Weedpacket

Arithmetic is the same. It wouldn't be very useful to one or another group of users if Excel or PHP had different ideas about how multiplication worked from everyone else.

$coin_cost = 117.00; // User input
$gold_eagle = 0.1; // User input
$spot_price = 845.30; // User input

$gold_content = $spot_price * $gold_eagle; // 117.00 * 0.1 = 84.53 in this example
$premium = $coin_cost - $gold_content; // 117.00 - 84.53 = 32.47 in this example

$percentage_premium = ceil(100*$premium/$coin_cost); // 28 in this example (the ceil() to round up).

I notice in your original code there is no subtraction, nor any conversion of the final fraction to a percentage.

jb3

Yes indeed, the subtraction was an oversight, and the % something I do not yet understand.

djjjozsi

hello,

in your original code $value_price is an undefined variable!

another suggestion:

if the user really send the form, and filled the three textfield, then start the calculation only:

if(!empty($_GET))
{
extract($_GET);

if(empty($pog_score) OR empty($amount_score) OR empty($asking_score))
die("Please fill all the forms!");
}

...

Weedpacket

jpb3 wrote:
and the % something I do not yet understand.

You do know how percentages work, right? (If you're thinking of the % operator, that's not for percentages.)