这本书的上半部分，你输出了一些东西，并且调用了函数，不过一切都是直线式进行的。你的脚本从最上面一行开始，一路运行到结束，但其中并没有确定程序流向的分支点。现在你已经学会了 `if`、`else`和 `elsif`，你就可以开始建立包含条件判断的脚本了。 上一个脚本中你写了一系列的简单提问测试。这节的脚本中，你将需要向使用者提问，依据使用者的答案来做出决定。把脚本写下来，多多捣鼓一阵子，看看他的运作原理是什么。 ~~~ def prompt print "> " end puts "You enter a dark room with two doors. Do you go through door #1 or door #2?" prompt; door = gets.chomp if door == "1" puts "There's a giant bear here eating a cheese cake. What do you do?" puts "1\. Take the cake." puts "2\. Scream at the bear." prompt; bear = gets.chomp if bear == "1" puts "The bear eats your face off. Good job!" elsif bear == "2" puts "The bear eats your legs off. Good job!" else puts "Well, doing #{bear} is probably better. Bear runs away." end elsif door == "2" puts "You stare into the endless abyss at Cthuhlu's retina." puts "1\. Blueberries." puts "2\. Yellow jacket clothespins." puts "3\. Understanding revolvers yelling melodies." prompt; insanity = gets.chomp if insanity == "1" or insanity == "2" puts "Your body survives powered by a mind of jello. Good job!" else puts "The insanity rots your eyes into a pool of muck. Good job!" end else puts "You stumble around and fall on a knife and die. Good job!" end ~~~ 这里的重点是你可以在 `if` 语句中内部再放一个 `if` 语句。这是一个很强大的功能，可以用来建立「巢状(nested)」的决定（decision)。 你需要理解` if `语句包含 `if` 语句的概念。做一下加分习题，这样你会确信自己真正理解了它们。 # 你应该看到的结果 * * * * * 我在玩一个小冒险游戏。我的水准不怎么样。 ~~~ $ ruby ex31.rb You enter a dark room with two doors. Do you go through door #1 or door #2? > 1 There's a giant bear here eating a cheese cake. What do you do? 1\. Take the cake. 2\. Scream at the bear. > 2 The bear eats your legs off. Good job! $ ruby ex31.rb You enter a dark room with two doors. Do you go through door #1 or door #2? > 1 There's a giant bear here eating a cheese cake. What do you do? 1\. Take the cake. 2\. Scream at the bear. > 1 The bear eats your face off. Good job! $ ruby ex31.rb You enter a dark room with two doors. Do you go through door #1 or door #2? > 2 You stare into the endless abyss at Cthuhlu's retina. 1\. Blueberries. 2\. Yellow jacket clothespins. 3\. Understanding revolvers yelling melodies. > 1 Your body survives powered by a mind of jello. Good job! $ ruby ex31.rb You enter a dark room with two doors. Do you go through door #1 or door #2? > 2 You stare into the endless abyss at Cthuhlu's retina. 1\. Blueberries. 2\. Yellow jacket clothespins. 3\. Understanding revolvers yelling melodies. > 3 The insanity rots your eyes into a pool of muck. Good job! $ ruby ex31.rb You enter a dark room with two doors. Do you go through door #1 or door #2? > stuff You stumble around and fall on a knife and die. Good job! $ ruby ex31.rb You enter a dark room with two doors. Do you go through door #1 or door #2? > 1 There's a giant bear here eating a cheese cake. What do you do? 1\. Take the cake. 2\. Scream at the bear. > apples Well, doing apples is probably better. Bear runs away. ~~~ # 加分习题 * * * * * 为游戏添加新的部分，改变玩家做决定的位置。尽自己能力扩充这个游戏，不过别把游戏弄得太诡异了。