1 require 'yaml'
  2 
  3 $cd_arr = Array.new
  4 
  5 $fn = 'cd_db.yml'
  6 
  7 class CD
  8     def initialize(arr)
  9         @name = arr[0]
 10         @artist = arr[1]
 11         @numtracks = arr[2]
 12     end
 13 
 14     def getdetails
 15         return [@name,@artist,@numtracks]
 16     end
 17 end
 18 
 19 
 20 # PopCD is a child class of CD.
 21 class PopCD < CD
 22 
 23     def initialize(arr)
 24         super(arr)
 25         @genre =arr[3]
 26     
 27 
 28         def getdetails
 29         return (super << @genre)
 30     end
 31 end
 32 
 33 class ClassicalCD < CD
 34     def initialize(arr)
 35         super(arr)
 36         @conductor = arr[3]
 37         @composer = arr[4]
 38     end
 39 
 40     def getdetails
 41         return (super << @conductor << @composer)
 42     end
 43 end
 44 
 45 #some methods to get data from the user
 46 
 47 def otherCD
 48     print("Enter CD name: ")
 49     cd_name = gets().chomp()
 50     print("Enter artist's name: ")
 51     a_name = gets().chomp()
 52     print("Enter number of tracks: ")
 53     num_tracks = gets().chomp().to_i
 54     return [cd_name,a_name,num_tracks]
 55 end
 56 
 57 def classicCD
 58     cdInfo = otherCD
 59     print("Enter conductor's name: ")
 60 
 61     con_name=gets().chomp()
 62     print("Enter composer's name: ")
 63     comp_name = gets().chomp()
 64     cdInfo << con_name << comp_name
 65     return cdInfo
 66 end
 67 
 68 def popCD
 69     cdInfo = otherCD
 70     print("Enter genre of music: ")
 71     genre = gets().chomp()
 72     cdInfo << genre
 73     return cdInfo
 74 end
 75 
 76 #add a CD object to the array variable , $cd_arr
 77 
 78 def addCD(aCD)
 79     $cd_arr << aCD
 80 end
 81 
 82 #save data to disk in YAML format
 83 
 84 def saveDB
 85     File.open($fn,'w'){
 86         |f|
 87         f.write($cd_arr.to_yaml)
 88     }
 89 end
 90 
 91 #loads data from disk and recreates the array of
 92 # cd objects, $cd_arr, from the data
 93 #
 94 def loadDB
 95     input_data = File.read($fn)
 96     $cd_arr = YAML::load(input_data)
 97 end
 98 
 99 #prints the data from the array to screen in human-
100 #readable(YAML) format
101 
102 def showData
103     puts($cd_arr.to_yaml)
104 end
105 
106 #Start of Program
107 
108 if File.exist?($fn) then
109     loadDB
110     showData
111 else
112     puts("The file #{$fn} cannot be found.")
113 end
114 
115 # 'main' loop
116 ans = ''
117 
118 until ans == 'q' do
119     puts("Create (P)op CD (C)lassical CD,(O)ther CD - (S)ave or (Q)uit?")
120     print("> ")
121     ans = gets[0].chr().downcase()
122     case ans
123         when 'p' then addCD(PopCD.new(PopCD()))
124         when 'c' then addCD(ClassicalCD.new(classicCD()))
125         when 'o' then addCD(CD.new(otherCD()))
126         when 's' then saveDB
127     end
128     showData
129 end