#!/usr/bin/perl


my $start = $ARGV[0];
my $apr = $ARGV[1];
my $months = $ARGV[2];
my $addto = $ARGV[3];

if ($months eq "") {
  print "Computes monthly compounding interest.\n";
  print "Usage: $0 <starting amount> <apr> <number of months> (amount additional investment each month)\n";
  exit;
}

if ($addto eq "") { $addto = 0; }

my $mpr = $apr / 12;

print "Monthly percentage rate is $mpr\n";
print "Begin: \$" . $start . "\n";

my $total_interest = 0;
my $total_invested = $start;
my $i = 0;
my $total = $start; 
while($i <= $months) {
  unless ($i == 0) { $total = $total + $addto; $total_invested = $total_invested + $addto }
  my $interest = $total * $mpr;
  $total_interest = $total_interest + $interest;
  $total = $total + $interest;
  printf("Month %02i Added: \$%i \$%.4f interest\tTotal: \$%.2f\n",$i,$addto,$interest,$total);
  $i++;
}

printf("Done. Made \$%.2f in interest, with an investment of \$%.2f\n",$total_interest,$total_invested);