# show loan interest

$i=0;
while ( $i < $#ARGV) {			# process args
   if ( @ARGV[$i] eq "-r" ) {
      $RATE=@ARGV[++$i];		# interest rate
   } else {
      if ( @ARGV[$i] eq "-a" ) {
         $AMOUNT=@ARGV[++$i];	# loan amount
      } else {
         if ( @ARGV[$i] eq "-p" ) {
            $PAYMENT=@ARGV[++$i];	# payment amount
         } else {
            print "Unknown argument (@ARGV[$i])\n";
            exit
         }
      }
   }
   $i++;
}

if ($AMOUNT == 0 || $RATE == 0 || $PAYMENT == 0) {
   print "Specify -r rate -a amount -p payment\n";
   exit
}

print "Original balance: \$$AMOUNT\n";
print "Interest rate:     ${RATE}%\n";
print "Monthly payment:  \$$PAYMENT\n";
print "\n";
print "Month\tPayment\tInterest\tPrincipal\tBalance\n\n";

$month=1;
$rate=$RATE/12/100;   	# get actual monthly percentage rate
$balance=$AMOUNT;
$payment=$PAYMENT;

while ($balance > 0) {
# round up interest amount
   $interest=roundUpAmount($rate * $balance);
   $principal=roundUpAmount($payment - $interest);
   if ( $balance < $principal ) {     # last payment
      $principal=$balance;     	# don't pay too much!
      $payment=$principal + $interest;
   }
   $balance = roundUpAmount($balance - $principal);
   print "$month\t\$$payment\t\$$interest\t\t\$$principal\t\t\$$balance\n";
   $month++;
}

sub roundUpAmount {
#
# in: floating point monetary value 
# out: value rounded (and truncated) to the nearest cent
#
   $value=$_[0];

   $newvalue = ( int ( ( $value * 100 ) +.5 ) ) / 100;

   return ($newvalue);
}