$a[0] = 5;
$a[1] = 3;
$a[3] = 15;
for($n = 0; $n < scalar (@a); $n++) {
  $b[n]=sprintf("%.2f", $a[n]);
}

print "$b[0]\n";
print "$b[1]\n";
print "$b[2]\n";
print "$b[3]\n";