案例陈述未按预期工作 [英] Case statement not working as expected

问题描述

我有一个名为 Exercises.rb

def ask(prompt)
  print prompt, ' '
  $stdout.flush
  s = gets
  return s
end

def myreverse(s)
  aux=""
  for i in 0..s.length-1
    aux=s[i] + aux
  end
  return aux
end

def mywordreverse(s)
  aux=[]
  s=s.split(" ")
  for i in 0..s.length-1
    aux.unshift(s[i])
  end
  return aux.join(" ")
end

def choose(s,option)
  case option
    when 1 then print myreverse(s)
    when 2 then print mywordreverse(s)
    when 3 then print "hello"
    else print "You gave me #{option} -- I have no idea what to do with that."
  end
end

s=ask("Write a string to reverse: ")
option=ask("Choose an option. 1 - Reverse string. 2 - Reverse String words : ")

choose(s,option)

我总是得到 你给了 MYCHOSENOPTION -- 我不知道该怎么做.，无论我选择什么选项.如果我在比较 1 的 case 之前放置一个 if，它似乎与我的字符串不匹配.

I am always getting You gave MYCHOSENOPTION -- I have no idea what to do with that., no matter what option I choose. If I put an if just before the case comparing 1, it just doesn't seem to be matching the option to my strings.

推荐答案

FWIW，我将如何编写这个程序:

FWIW, here is how I would write this program:

def ask(prompt)
  print "#{prompt} "
  gets.chomp
end

def myreverse(s)
  s.reverse
end

def mywordreverse(s)
  s.split(' ').reverse.join(' ')
end

def choose(s,option)
  case option
    when 1 then puts myreverse(s)
    when 2 then puts mywordreverse(s)
    when 3 then puts "hello"
    else        puts "You gave me #{option}; I don't know what to do with that."
  end
end

$stdout.sync
str    = ask("Write a string to reverse: ")
option = ask("Choose an option:\n1: Reverse string\n2: Reverse String words\n>")
choose(str,option.to_i)

注意事项:

1. 方法中的最后一个表达式是返回值；在 Ruby 中几乎不需要或不需要使用 return.
2. 存在用于反转字符串和数组的内置方法.(我理解你这样做是为了练习.)

3. 在 Ruby 中使用 for 迭代数组或字符串很麻烦.相反，您应该使用

1. The last expression in a method is the return value; using return is almost never needed or desirable in Ruby.
2. There exist built-in methods for reversing strings and arrays. (I understand if you are doing this for an exercise.)

3. It is cumbersome to iterate arrays or strings in Ruby using for. Instead, you should use

my_str.each_char do |char|
  # use the single-character string `char` here
end

my_array.each do |item|
  # use the item here
end

您可以使用 $stdout.sync 强制输出总是被刷新.

You can use $stdout.sync to force output to always be flushed.

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