[Resolved] "invalid arguments" with pow()

[Strings]

I'm trying to create a basic car loan calculator, I'm stumped. The Loan Amount, Interest Rate and duration is typed in by the user via an html form. I don't know why pow() keeps on giving me warnings that the arguments that I pass to it aren't valid when they are numbers. I am required to use the pow() for this script. Here's the code in question:

<?php

$LoanAmt=$_POST["LoanAmount"];
$IntrRate=$_POST["InterestRate"]/100;
$duration=$_POST["NumMonths"];

if(is_numeric($LoanAmt)==true && is_numeric($IntrRate)==true && is_numeric($duration)==true)
{
 $Payment1 = $LoanAmt * ($IntrRate / 12);
 $Payment2 = pow(1 + ($IntrRate / 12),$duration);
 $Payment3 = pow(1 + ($IntrRate / 12),$duration) - 1;
 $MonthlyPayment = $Payment1 * ($Payment2 / $Payment3);
 print "$MontlyPayment";
}
else
{
  print "Please enter only numeric values";
}

?>

[dalecosp]

I don't think you wanna check (==true):

if(is_numeric($LoanAmt) && is_numeric($IntrRate) && is_numeric($duration))

Also, there are some good debugging tips in the "Debugging 101" thread in this forum.

HAND,

[laserlight]

I tested your code, except that I changed $POST to $GET in order to use the query string.
I didnt get any errors with error reporting set at E_ALL, after correcting your typo.

I'd say that the problem is probably because pow() requires numbers, while numeric strings are entered.
A solution is to typecast the variables, e.g.

<?php

$LoanAmt = $_POST["LoanAmount"];
$IntrRate = $_POST["InterestRate"];
$duration = $_POST["NumMonths"];

if (is_numeric($LoanAmt) && is_numeric($IntrRate) && is_numeric($duration))
{
	$IntrRate /= 1200; // divided by 100, then by 12
	$Payment1 = $LoanAmt * $IntrRate;
	$IntrRate++;
	$Payment2 = pow((float)$IntrRate, (int)$duration); //typecast
	($Payment2 != 1) ? ($Payment2 /= $Payment2 - 1) : die('Division by zero');
	$MonthlyPayment = $Payment1 * $Payment2;
	echo 'Monthly Payment: ' . $MonthlyPayment;
}
else
{
	echo "Please enter only numeric values";
}

?>

I did simplify your code in order to remove redundant calculations and expressions.

[Strings]

Thanks for the help. I also thought it was a problem with numeric strings, but I just didn't know how to solve it.