Return 来自嵌套子例程 Perl 的值

Question

我们收到了学校的作业，我们应该在其中制作我们自己的小型简单 Perl 应用程序。我想我会做一个 ATM 模拟器。到目前为止，一切进展顺利；我使用子程序创建了一个菜单（取款、余额、转账）。到目前为止，这是我的代码：

#! /usr/bin/perl
#Written by: Tobias Svenblad, h15tobsv@du.se, Digitalbrott & e-Säkerhetsprogrammet (2015)
#PerlLab03-2c.plx

use warnings;
use strict;
use Term::ANSIColor;
use Text::Format;

my $firstname;
my $lastname;
my $acc_balance = 2451.26;
my $acc_withdraw;
my $clr_scr = join( "", ( "3[2J", "3[0;0H" ) );    #This variable will clear the screen and jump to postion 0, 0.

my $atm = Text::Format->new;
print color('green');
print $atm->center("ATM v. 1.20");
print color('reset');

#Create account message.
my $crt_acc_msg = <<"END_MSG";
\nDear Sir or Madam,\n
We're very happy you've chose us as your bank.
Before we proceed, we need to set-up your account.\n
END_MSG

print $crt_acc_msg;

&acc_create;
&acc_choose;

sub acc_create {
  ACC_BEGINNING:

    #First name:
    print "\nYour first name: ";
    $firstname = <STDIN>;
    chomp $firstname;

    #Last name:
    print "\nYour last name: ";
    $lastname = <STDIN>;
    chomp $lastname;
    if ( defined($firstname) && $firstname ne "" ) {
        if ( defined($lastname) && $lastname ne "" ) {
            goto ACC_PASS;
        }
    }
    else {
        print "You didn't fill in first or last name. Try again. \n";
        goto ACC_BEGINNING;
    }
  ACC_PASS:
    print "Please wait while the system loads.\n\n";

    #sleep(2);
    print $clr_scr;

    print color('green');
    print $atm->center("ATM v. 1.20");
    print color('reset');

    print "\nWelcome ", $firstname, " ", $lastname, "!\n\n";
}

sub acc_choose {

    sub acc_balance {
        print $clr_scr;

        print color('green');
        print $atm->center("ATM v. 1.20");
        print color('reset');

        print "\nYour balance is: ";
        print color('green');
        print $acc_balance;
        print color('reset');
        print " SEK\n\n";
        &acc_choose;
    }

    sub acc_withdraw {

      ENTER_AMOUNT:
        print $clr_scr;

        print color('green');
        print $atm->center("ATM v. 1.20");
        print color('reset');

        print "\nEnter how much you'd like to withdraw: \n";
        my $acc_balance_withdraw = <STDIN>;

        if ( $acc_balance_withdraw > $acc_balance ) {
            print "Insufficient funds.";
            goto ENTER_AMOUNT;
        }
        $acc_balance -= $acc_balance_withdraw;
        print "\nYour current balance is now: ";
        print color('green');
        print $acc_balance;
        print color('reset');
        print " SEK\n\n";
        &acc_choose;
    }

    sub acc_transfer {
      ENTER_AMOUNT:
        print $clr_scr;

        print color('green');
        print $atm->center("ATM v. 1.20");
        print color('reset');

        print "\nEnter how much you'd like to transfer: \n";
        my $acc_balance_withdraw = <STDIN>;

        if ( $acc_balance_withdraw > $acc_balance ) {
            print "Insufficient funds.";
            goto ENTER_AMOUNT;
        }

        print "\nYour current balance is now: ";
        print color('green');
        print $acc_balance - $acc_balance_withdraw;
        print color('reset');
        print " SEK\n\n";
        &acc_choose;
    }
  ACC_CHOOSE:
    print "[ ";
    print color('cyan');
    print "1";
    print color('reset');
    print " ]";
    print "Account Balance\n";
    print "[ ";
    print color('cyan');
    print "2";
    print color('reset');
    print " ]";
    print "Withdraw\n";
    print "[ ";
    print color('cyan');
    print "3";
    print color('reset');
    print " ]";
    print "Transfer\n";
    my $choice1 = <STDIN>;
    chomp $choice1;

    if ( $choice1 == 1 ) {
        &acc_balance;
    }
    elsif ( $choice1 == 2 ) {
        &acc_withdraw;
    }
    elsif ( $choice1 == 3 ) {
        &acc_transfer;
    }
    else {
        print "You entered an invalid option. Try again. \n";
        goto ACC_CHOOSE;
    }
    return ();
}

我遇到的问题是当我尝试将 return 的 $acc_balance 值传递给其他子例程时。我试图在嵌套子例程下实现 return($acc_balance );，但这只会提示我结束应用程序。所以基本上，我想做的是每次提款或转账时更新 $acc_balance（它们目前在这段代码中是同一件事），但每当我尝试这样做时，它要么不'更新值，否则它只会显示经典的 "Press any key to continue..." 消息。

非常感谢任何帮助！谢谢！

Answer 1

看起来很可爱，但有些事情是不应该做的。我将尝试向您展示选择部分。

不要使用 & 调用子程序，而是使用括号，即 acc_choose(); 而不是 &acc_choose;。

不要在 perl 中嵌套 functions/subs。如果你真的想封装东西（我很欣赏并推荐），使用模块。但这超出了这个问题的范围。稍后你会了解到。

如果不是绝对必要，请不要使用 goto。它使控制流程变得怪异、难以遵循，并且经常导致意外。

如果你想重复某事直到满足某个条件——或者换句话说——while某个条件没遇见，使用 while 循环。

鉴于此，我建议 choose 部分（省略花哨的印刷）：

sub acc_balance {
    print "\nYour balance is: $acc_balance SEK\n\n";
}

sub acc_withdraw {
    my $acc_balance_withdraw = 0;

    do {
        print "\nEnter how much you'd like to withdraw: \n";
        $acc_balance_withdraw = <STDIN>;

        if ( $acc_balance_withdraw > $acc_balance ) {
            print "Insufficient funds.\n";
        }
    } while( $acc_balance_withdraw > $acc_balance );

    # if you get here, then $acc_balance_withdraw <= $acc_balance, so:      
    $acc_balance -= $acc_balance_withdraw;
    print "\nYour current balance is now: $acc_balance SEK\n\n";
}


# actually almost the same as acc_withdraw() only with
# other screen output and no `-=` operation 
sub acc_transfer {
    # left as an excercise
}


sub acc_choose {

    print "[1] Account Balance\n";
    print "[2] Withdraw\n";
    print "[3] Transfer\n";
    print "[4] Exit\n";

    do {
        my $choice1 = <STDIN>;
        chomp $choice1;

        if ( $choice1 == 1 ) {
            acc_balance();
        }
        elsif ( $choice1 == 2 ) {
            acc_withdraw();
        }
        elsif ( $choice1 == 3 ) {
            acc_transfer();
        }
        elsif ( $choice1 == 4 ) {
            print "Thank you. Good bye.\n"
        }
        else {
            print "You entered an invalid option. Try again. \n";
        }
    } while( $choice != 1 && $choice != 2 && $choice != 3 && $choice != 4 );
}

您尝试的一个问题可能是您递归地调用了 acc_choose()，即您是从其内部调用它。再加上goto确实可以起到很好的娱乐效果。

祝你好运，继续加油。

哦，然后回答你的问题：现在拥有子例程 return 东西真的很简单。这不是必需的，因为你使用 $acc_balance 的全局变量（也不要这样做），但如果你愿意，你可以让 subs return 像这样的新余额：

sub acc_withdraw {
    my $old_balance = shift; # that's the first argument given to this sub
    my $acc_balance_withdraw = 0;

    do {
        print "\nEnter how much you'd like to withdraw: \n";
        $acc_balance_withdraw = <STDIN>;

        if ( $acc_balance_withdraw > $old_balance ) {
            print "Insufficient funds.\n";
        }
    } while( $acc_balance_withdraw > $old_balance );

    # if you get here, then $acc_balance_withdraw <= $acc_balance, so:      
    my $new_balance = $old_balance - $acc_balance_withdraw;
    print "\nYour current balance is now: $new_balance SEK\n\n";
    return $new_balance;
}

# and then...

$acc_balance = acc_withdraw($acc_balance);

Answer 2

我删除了格式和颜色，因为它与问题无关。方法如下：子例程需要的所有内容都来自其参数，它更改的所有内容都将返回。

#! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

sub create {
    print << 'END_MSG';

Dear Sir or Madam,

We're very happy you've chose us as your bank.
Before we proceed, we need to set-up your account.

END_MSG

    my ($firstname, $lastname);

    my $first = 1;
    while (! defined $firstname || ! defined $lastname
           || q() eq $firstname || q() eq $lastname
          ) {
        say "You didn't fill in first or last name. Try again." unless $first;
        undef $first;

        print "\nYour first name: ";
        chomp( $firstname = <STDIN> );

        print "\nYour last name: ";
        chomp( $lastname = <STDIN> );
    }

    say "Please wait while the system loads.\n";

    say "\nWelcome ", $firstname, " ", $lastname, "!\n";
    return ($firstname, $lastname)
}

sub choose {
    my $balance = 2451.26;
    my @menu = ( 'Account Balance',
                 'Withdraw',
                 'Transfer',
                 'Quit',
               );
    my $choice = q();

    until ('4' eq $choice) {
        for my $i (0 .. $#menu) {
            say '[ ', $i + 1, ' ] ', $menu[$i];
        }

        chomp( $choice = <STDIN> );

        my @actions = (\&balance,
                       \&withdraw,
                       \&transfer,
                       sub {}
                      );
        my $action = $actions[$choice - 1];

        if ($action) {
            my $value = $action->($balance);
            $balance = $value if defined $value;
        } else {
            say 'You entered an invalid option. Try again.';
        }
    }
}

sub balance {
    my $balance = shift;
    say "\nYour balance is: $balance SEK\n\n";
    return $balance
}

sub withdraw {
    my $balance = remove('withdraw', @_);
    return $balance
}

sub transfer {
    my $balance = remove('transfer', @_);
    return $balance
}

sub remove {
    my ($action, $balance) = @_;

    say "\nEnter how much you'd like to $action:\n";
    my $remove = <STDIN>;

    if ( $remove > $balance ) {
        print "Insufficient funds.";
    } else {
        $balance -= $remove;
    }
    balance($balance);
}

my ($firstname, $lastname) = create();
choose();
say "Good bye, $firstname $lastname!";

嵌套子程序的嵌套方式与 Pascal 不同。事实上，您不能在 Perl 中嵌套命名子例程。

如图所示，只有在需要引用子例程时才使用&。

不要使用 goto。循环更容易理解和管理。

此外，请确保不要在打印重要消息后立即擦除屏幕 ("Insufficient funds")。

Answer 3

我认为您不应该为这项作业使用子例程。但令我担心的是，有人告诉您在调用子例程时要使用 & 符号 &，并解释了如何使用标签和 goto。这不适合现代计算机语言，您可以做得更好

例如，我会这样写你的子程序acc_create

sub acc_create {

    while () {

        print "\nYour first name: ";
        chomp (my $firstname = <STDIN>);

        print "\nYour last name: ";
        chomp (my $lastname = <STDIN>);

        last if $firstname and $lastname;

        print "You didn't fill in first or last name. Try again.\n";
    }

    print "Please wait while the system loads.\n\n";

    print
        $clr_scr,
        color('green'), $atm->center("ATM v. 1.20"), color('reset');

    print "\nWelcome $firstname $lastname!\n\n";
}

我还有很多话要说，但 Stack Overflow 不是教程的地方

Return 来自嵌套子例程 Perl 的值

Return value from nested Subroutine Perl

perl

nested

subroutine