在我的程序中收到错误"整数到字符串没有隐式转换"

Question

我正在创建一个基于文本的音乐播放器程序。

在Read_genre((函数中显示可用类型的列表(我在rade_gerre((函数之外定义了9种不同类型的列表$，其中读取用户输入的类型编号。然后从read_album调用read_genre并在print_album函数中打印出来。

问题在于，我正在收到错误'nill不隐含转换为字符串(typeError('第134行，该行是从print_album((函数中添加的 Genre is ' + album.genre。

$genre_names = ['Null','Pop', 'Classic', 'Jazz', 'Rock', 'KPop', 'Metal', 'Punk', 'Romance', 'Latin']
# Display the genre names in a
# numbered list and ask the user to select one
def read_genre()
    length = $genre_names.length
    index = 0
    print $genre_names
  while (index < length)
    select_genre = read_integer_in_range("Select Genre: ", 0,9)
        case select_genre
        when 1
        puts "#{index + 1} " + $genre_names[1]
        break
        when 2
        puts "#{index + 2 } " + $genre_names[2]
        break
        when 3
        puts "#{index + 3} " + $genre_names[3]
        break
        when 4
        puts "#{index + 4} " + $genre_names[4]
        break
        when 5
        puts "#{index + 5} " + $genre_names[5]
        break
        when 6
        puts "#{index + 6} " + $genre_names[6]
        break
        when 7
        puts "#{index + 7} " + $genre_names[7]
        break
        when 8
        puts "#{index + 8} " + $genre_names[8]
        break
        when 9
        puts "#{index + 9} " + $genre_names[9]
        break
         else
          puts 'Please Select again'
          break 
        end
        index
    end
end
def read_album
    # Complete the missing code
  album_title = read_string("Enter Title: ")
  album_artist = read_string("Enter Artist name: ")
  album_genre = read_genre()
  tracks = [tracks]
  album = Album.new(album_title, album_artist, album_genre, tracks)
  album
end

def print_tracks tracks
    # Complete the missing code
    index = 0
    while (index < tracks.length)
     print_track(tracks[index])
     index += 1
    end
end

Answer 1

您在main方法中定义了music_file，但是您正在尝试在其他未定义的方法中访问它，因此错误。

让我们分析您的代码在做什么：

def search_for_track_name(tracks, search_string)
index = 0
count = music_file.gets() 
# Trying to access a variable that is outside of the method's scope
# music_file doesn't exist here.
while (index < count)
    if (tracks[index] == search_string)
        return found_index = -1
        # You are returning -1 if the condition is true, which means
        # returning -1 when the string is found even though you want
        # the exact opposite.
    end
    index += 1
end
 found_index
 # If the pointer gets here, it means that the if statement was never true
 # therefore found_index was never defined
end

让我们解决以下问题：

def search_for_track_name(tracks, search_string)
index = 0
count = tracks.length
# will loop through the array's items
while (index < count)
    if (tracks[index] == search_string)
        return index
        # will return index if found
    end
    index += 1
end
  -1
  # if the loop finishes and nothing is found, will return -1
end

，或者您可以使用 index方法，该方法返回数组中元素的第一匹匹配的索引。

tracks.index(search_string)

https://ruby-doc.org/core-2.6.3/array.html#method-i-index