通过提问来获得减分的风险,我正在为Perl口译员提出的错误寻求帮助。这是Beginning Perl的作业问题。
问:修改货币计划以继续询问货币名称,直到输入有效的货币名称。
#! /usr/bin/perl
#convert.pl
use warnings;
use strict;
my ($value, $from, $to, $rate, %rates);
%rates = (
pounds => 1,
dollars => 1.6,
marks => 3,
"french frances" => 10,
yen => 174.8,
"swiss frances" => 2.43,
drachma => 492.3,
euro => 1.5
);
print "currency exchange formula -
pounds, dollars, marks, french frances,
yen, swiss frances, drachma, euro\n";
print "Enter your starting currency: ";
$from = <>;
chomp($from);
While ($from ne $rates{$from}) {
print "I don't know anything about $from as a currency\n";
print "Please re-enter your starting currency:";
$from = <>;
chomp($from);
}
print "Enter your target currency: ";
$to =<>;
chomp($to) ;
While ($to ne $rates{$to}) {
print "I don't know anything about $to as a currency\n";
print "Please re-enter your target currency:";
$to = <>;
chomp($to);
}
print "Enter your amount: ";
$value = <>;
chomp ($value);
if ($value == 0) {
print "Please enter a non-zero value";
$value = <>;
chomp ($value);
}
$rate = $rates{$to} / $rates{$from};
print "$value $from is ", $value*$rate, " $to.\n";
确定了4个错误,所有错误都在while
循环中,例如"syntax error at line 27, near ") {"
或...at line 33, near "}"
...等。我唯一拥有的内容,例如第27行,是")"
和"{"
之间的空格。就我所见,作者提供的解决方案几乎与我的脚本一致,除了作者使用while (not exists $rates{$from}) { ... }
。
我是否误解了“ne”的用法?或者我的脚本有什么问题吗?非常感谢。
答案 0 :(得分:5)
您的While
以大写W 开头。
Perl区分大小写,应该是while
。
如前所述使用while (not exists $rates{$from}) { ... }
是正确的。在您的代码中,您将字符串$from
与$from
哈希中与 %rates
对应的数字进行比较。无论如何,这都不是真的。
答案 1 :(得分:3)
ne
“不等于”。你的第一个while
循环使用它,但它永远不会像你写东西那样得到错误的条件。你将永远陷入那个循环中。一个单词永远不会匹配一个数字。这就是为什么你要检查密钥是否not exists
。
正确的做法是打印出您知道的货币,例如: say for keys %rates
并使用do {...} while (...)
循环。
而且,正如Cthulhu所说,你正在调用While
而不是正确的while
。