if语句在Lua中对io.read不起作用

Question

我想做一个'简单'的Y/N答案选择的事情。(你在旧程序中经常看到)但是我正在使用的If语句似乎不想工作。我甚至打印出了变量，它离我想要比较的值远得多，但它仍然传递了它。

        --Porgram Functions
        function check()
        --Local Variables
            local num = 0
            local loop = true
            io.write("Continue? (Y/N):")
            --User input
            local input = io.read()
            while(loop==true) do
                if (input=="y" or "Y") then
                    print("Ok!")
                    loop = true
                    num = 1
                elseif (input=="n" or "N") then
                    print("Fine...")
                    num = 2
                else
                    print("Invalid Answser!")
                    loop = true
                    num = 0
                end
            end
            print(input)
            return(num)
        end
        print (check())

Answer 1

我会这样写你的函数:

function check()
    io.write("Continue? (Y/N): ")
    answer = io.read()
    while( not (answer == "Y" or answer == "N") ) do
        io.write("Invalid Answer! Try again (Y/N): ")
        answer = io.read()
    end
    if answer == "Y" then
        print("Ok!")
        return 1
    else
        print("Fine...")
        return 2
    end
end
print(check())

使用的一些例子:

Continue? (Y/N): Huh?
Invalid Answer! Try again (Y/N): N
Fine...
2
>Exit code: 0
>lua -e "io.stdout:setvbuf 'no'" "a.lua" 
Continue? (Y/N): Huh?
Invalid Answer! Try again (Y/N): Y
Ok!
1

---

你的代码的工作版本应该是:

function check()
    local num = 0
    local loop = true    
    io.write("Continue? (Y/N):")
    while(loop==true) do    
        --User input
        local input = io.read()   
        if (input == "y" or  input == "Y") then    
            print("Ok!")
            num = 1
            loop = false --we want to stop looping if input is valid      
        elseif (input == "n" or input == "N") then    
            print("Fine...")
            num = 2
            loop = false --we want to stop looping if input is valid   
        else
            print("Invalid Answser!")
            -- loop = true no need to set looping to true again
            num = 0    
        end
    end
    return(num)
end

所做的更改如下:

1. 在 while循环中获取用户输入，这样，如果输入无效并且循环再次使用获取输入背后的相同逻辑，我们不必为获取输入编写两种情况;一个在循环外，一个在循环内。当循环再次开始时，也会暂停的执行，这就是产生所有输出的原因!
2. input == "y" or "Y"不做你想的那样。相反，它的计算结果是(input == "y") or ("Y")，你想要的是input == "y" or input == "Y"。
3. 当输入为"y" or "Y" or "n" or "N"时，您需要将循环设置为false，否则循环将继续。
4. 第四，在循环内部将循环设置为true是不必要的，它从true开始，您唯一可以做的更改是将其设置为false。由于每个条件都是互斥的，即输入为"y" or "Y"与输入为"n" or "N"互斥，或者既不 "y" or "Y"也不 "n" or "N"。你不需要担心它被设置为false，除非你想要循环结束。

Answer 2

local function check()
   io.write"Continue? (Y/N): "
   local ans, num = {y = 1, n = 2}
   repeat
      num = ans[io.read():lower()] or 3
      io.write(({"Ok!n","Fine...n","Invalid Answer! Try again (Y/N): "})[num])
   until num < 3
   return num
end
print (check())