Introduction to Perl Language-4th Chapter-sub-Program

subroutine definition and return value

Sub sum{    print" called sub-program \ n";     $a $b # The latter behavior returns a value }$a=1; $b=; $s # 34 Calling Subroutines

Sub-program parameters, parameters fixed (The following example can only 2 parameters), the first parameter of the program is $_[0], the second is $[1], and so on

Sub Max {    if($_[0$_[1]) {        $_[  0];    } Else {        $_[1];    }} $n = & Max (the result is

Private variables in subroutines

Sub Max {    my($m,$n@_;}

Limit parameter length

Sub max{    if(@_2) {        print"  waring! &max arguments not match"    }}

Variable-length parameter list

SubMax {my($max _num) =Shift @_;#the first value in the array    foreach(@_){        if($_>$max _num){            $max _num=$_; }    }    $max _num;}$maximum= &max (1,6,Ten,5, -,9);Print $maximum

About my variables

my ($num@_# List Context my$num@_# Header Context my @_;

preferably using use strict;

Use 5.012 #自动加载strict编译指令

return operator

If like in a child function, the foreach end can be terminated with the return operator.

Omit & and sign

The general situation can be omitted, if it is defined with the same name as the built-in function, such as chomp, it cannot be omitted, the call must be &chomp;

Non-header return value

Sub sum{   1.. Ten ;}

Persistent private variable state, if you use global variables in strict mode, you will get an error.

 UseStrict; Usefeature QW (state);Submarine{ State$n=0; $n+=1; Print "$n \ n";}&marine;#1&marine;#2&marine;#3

Introduction to Perl Language-4th Chapter-sub-Program