這本書的上半部分，你印出了一些東西，並且呼叫了函式，不過一切都是直線式進行的。你的腳本從最上面一行開始，一路運行到結束，但其中並沒有決定程式流向的分支點。現在你已經學會了?`if`、`else`和?`elsif`，你就可以開始建立包含條件判斷的腳本了。 上一個腳本中你寫了一系列的簡單提問測試。這節的腳本中，你將需要向使用者提問，依據使用者的答案來做出決定。把腳本寫下來，多多搗鼓一陣子，看看他的運作原理是什麼。 ~~~ 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 ~~~ 這裡的重點是你可以在?`if`?語句中內部再放一個?`if`?語句。這是一個很強大的功能，可以用來建立「巢狀(nested)」的決定（decision)。 你需要理解?`if`?語句包含?`if`?語句的概念。做一下加分習題，這樣你會確信自己真正理解了它們。 ## 你應該看到的結果 我在玩一個小冒險遊戲。我的水準不怎麼樣。 ~~~ $ 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. ~~~ ## 加分習題 為遊戲添加新的部分，改變玩家做決定的位置。盡自己能力擴充這個遊戲，不過別把遊戲弄得太詭異了。