《perl 语言入门》习题 第四章

1-3.

sub total {
        my $sum = shift @_;

        foreach $a (@_) {
                $sum += $a;
        }

        return $sum;
}

sub average {
        my($sum, $number) = @_;

        return $sum/$number;
}

#my @fred = 1..1000;
#my $fred_total = total(@fred);
#print "The total is $fred_total\n";

sub above_average {
        my @numbers = @_;
        my $number = @numbers;
        my $mean = average(total(@numbers),$number);
        my @out = ();

        foreach $a (@_) {
                if ($a > $mean) {
                        push(@out, $a);
                }
        }

        return @out;
}


my @fred = above_average(1..10);
print"\@fred is @fred\n"

4.

my $prev_person = undef;

sub greet {
        my ($person) = @_;

        if (!defined($prev_person)) {
                print "Hi, $person! You the first one here!\n";
        } else {
                print "Hi, $person! $prev_person is also here!\n";
        }
        $prev_person = $person;
}

my @persons = ();
sub greet2 {
        my ($person) = @_;

        if (@persons == 0) {
                print "Hi, $person! You the first one here!\n";
        } else {
                print "Hi, $person! I've seen: @persons \n";
        }
        push (@persons, $person);
}
greet2("Fred");
greet2("Barney");
greet2("zhenhua")