###ex4_1.pl
#!/usr/bin/perl -w
use strict;
sub total {
my ($sum,$sum,number);
$sum=0;
foreach $number (@_){
$sum+=$sum+=number;
}
KaTeX parse error: Expected 'EOF', got '#' at position 5: sum;#̲这个将sum返回给调用者
}
#子程序total使用$sum来存储总和
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:\n”;
my $user_total = total();
print “The total of those numbers is $user_total.\n”;

####ever think $number=shift @_;

#!/usr/bin/perl -w
use strict;
sub total {
my ($sum,$sum,number);
$sum=0;
foreach $number (@_){
$sum+=$sum+=number;
}
KaTeX parse error: Expected 'EOF', got '#' at position 5: sum;#̲这个将sum返回给调用者
}
print “the sum of 1000! is “,total(1…1000),”.\n”;
#注意不能在双括号括住的字符串里直接调用子程序，所以子程序调用的是print的另一个独立参数

###ex4_3.pl
#!/usr/bin/perl -w
use strict;
sub total {
my ($sum,$sum,number);
$sum=0;
foreach $number (@){
$sum+=$sum+=number;
}
KaTeX parse error: Expected 'EOF', got '}' at position 7: sum; }̲ sub average { …all)=1;
my($result)[email protected];
foreach(@){
$result+=$result+=;
$all=$all=all+1;
}
return $result/$result/all;
}
sub above_average {
my($mean)=&average(@_);
my $every;
my @list;
foreach KaTeX parse error: Expected '}', got 'EOF' at end of input: …y (@_){ if (every > KaTeX parse error: Expected '}', got 'EOF' at end of input: … push @list,every;#此处必须加$every，否则无法输出？
}
}
@list;
}
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”;

#!/usr/bin/perl -w
use strict;
sub greet {
my $first=shift @_; print "HI,$first=shift@;​print"HI,first!you are the first one here!\n";
my $later=shift @_; print "hi,$later=shift@;​print"hi,later,$first is also here!\n";
}
greet (“fred”,“barney”)

#!/usr/bin/perl -w
use strict;
sub greet {
my $first=shift @_; print "HI,$first=shift@;​print"HI,first!you are the first one here!\n";
my $second=shift @_; print "hi,$second=shift@;​print"hi,second! I’ve seen: $first\n";
my $third=shift @_; print "hi,$third=shift@;​print"hi,third! I’ve seen: $first $second\n";
my $fourth=shift @_; print "hi,$fourth=shift@;​print"hi,fourth! I’ve seen: $first $second $third\n";
}
greet (“fred”,“barney”,“wilma”,“betty”)

小笔记
@是函数传参时放置参数的数组，可以从中取实参
比如my($pa1,$pa1,pa2…)[email protected]，函数调用时填了几个参数，便可以从该数组中取到几个参数

$_是默认参数的意思，指的是在不指定的情况下，程序处理的上一个变量

欣洁的代码运行出来从第二行开始前面出现空格的问题：
不要加双引号，因为数组里的元素默认是要用空格分割的，用双引号把所有元素拼成一个字符串，不用双引号则分别输出各个元素

perl的内置警告信息
use warnings;
warnings比-w更灵活，它可以选择只对文件中使用了该编译指令的部分代码开启警告功能，而-w选项则不加区分，对整个程序中涉及的所有代码都开启警告功能

-w

use diagnostics; 这个编译命令报告更为详尽的问题描述；输出相关的错误信息，但程序启动变慢，可以通过-Mdiagnostics 来实现

W的意思是警告级别属于普通警告，numeric是警告类型属于数字操作一类