I found a odd question when i wanna round a float number
with Perl buildin function "sprintf" my code is

use warnings;
use strict;

my $price1   = sprintf("%.1f",100.550);
my $price2   = sprintf("%.0f",100.50);
print "$price1\n";  # price1  has rounded
print "$price2\n";  # but price2 hasn't , Why?
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Of course, i can use the manual round function like some referrence:

sub round {
  my $f = @_;
  return int($f + .5);
}
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But the question is Why $price1 has been rounded and price2 has not been rounded?