《Perl语言入门》第四版习题（4）

1. 写一个名为&total 的子程序，返回一列数字的和。提示：子程序不应当有任何的I/O 操作；它处理调用的参数，返回处理后的值给调用者。结合下面的程序来练习，它检测此子程序是否正常工作。第一组数组之和我25。
   my @fred = qw{ 1 3 5 7 9 };
   my $fred_total = &total(@fred);
   print "The total of /@fred is $fred_total./n";
   print "Enter some numbers on separate lines: ";
   my $user_total = &total(<STDIN>);
   print "The total of those numbers is $user_total./n";
2. 利用上题的子程序，写一个程序计算从1 到1000 的数字的和。
3. 额外的练习：写一个子程序，名为&above_average，将一列数字作为其参数，返回所有大于平均值的数字（提示：另外写一个子程序来计算平均值，总和除以数字的个数）。利用下面的程序进行测试：
   my @fred = &above_average(1..10);
   print "/@fred is @fred/n";
   print "(Should be 6 7 8 9 10)/n";
   my @barney = &above_average(100, 1..10);
   print "/@barney is @barney/n";
   print "(Should be just 100)/n";

1:
#!/usr/bin/perl -w
#<Leanning Perl 4th Edition> Exercise 4-1
use strict;

sub total {
    my $sum=shift @_;
    foreach (@_) {
    $sum=$sum+$_;
    }
    $sum;
}

my @fred=qw {1 3 5 7 9};
my $fred_total=&total(@fred);
print "The Total of /@fred is $fred_total./n";

print "Enter some numbers on separate lines: ";
my $user_total = &total(<STDIN>);
print "The Total of those numbers is $user_total./n";

2:
#!/usr/bin/perl -w
#<Leanning Perl 4th Edition> Exercise 4-2
use strict;

sub total {
    my $sum=shift @_;
    foreach (@_) {
    $sum=$sum+$_;
    }
    $sum;
}

my @array=1 .. 1000;
my $array_total=&total(@array);
print "The sum of 1 to 1000 is $array_total./n";

3:
#!/usr/bin/perl -w
#<Leanning Perl 4th Edition> Exercise 4-3
use strict;

sub average {
    my $number=@_;
    my $sum=shift @_;
    foreach (@_) {
    $sum=$sum+$_;
    }
    my $array_average=$sum/$number;
}

sub above_average {
    my @above;
    foreach (@_) {
        if ($_>&average(@_)) {
        push @above,$_;
        }
    }
@above;
}

my @above_fred = &above_average(1 .. 10);
print "The above average of /@fred is @above_fred/n";

my @above_barney = &above_average(100, 1 .. 10);
print "The above average of /@barney is @above_barney/n";