diff --git a/01-hello.rb b/01-hello.rb
index e0e7bbf..5d9711b 100644
--- a/01-hello.rb
+++ b/01-hello.rb
@@ -1,8 +1,8 @@
 # 题目: 输入名字，输出 "Hello, 名字"
 
-print "请输入你的名字，然后按 Enter: "
+print '请输入你的名字，然后按 Enter: '
 your_name = gets
 
 # ...
 
-puts "(请替换成最后的答案)"
\ No newline at end of file
+puts "hello, #{your_name} "
diff --git a/02-variable.rb b/02-variable.rb
index a5a4753..901b6e1 100644
--- a/02-variable.rb
+++ b/02-variable.rb
@@ -11,3 +11,9 @@
 puts "a 应该是 2，现在是 #{a}"
 puts "b 应该是 1，现在是 #{b}"
 
+c = a
+a = b
+b = c
+
+puts "a 现在是 #{a}"
+puts "b 现在是 #{b}"
diff --git a/03-triangle.rb b/03-triangle.rb
index fafec03..1d7e8ce 100644
--- a/03-triangle.rb
+++ b/03-triangle.rb
@@ -1,11 +1,11 @@
 # 题目: 使用者输入直角三角形的宽和高，输出三角形的面积
 
-print "请输入直角三角形的高，然后按 Enter: "
+print '请输入直角三角形的高，然后按 Enter: '
 a = gets
 
-print "请输入直角三角形的底边，然后按 Enter: "
+print '请输入直角三角形的底边，然后按 Enter: '
 b = gets
 
 # .....
-
-puts "直角三角形的面积是: _________"
\ No newline at end of file
+c = (a.to_i * b.to_i) / 2
+puts "直角三角形的面积是: #{c} "
diff --git a/04-pizzas.rb b/04-pizzas.rb
index 4c2521f..8c220df 100644
--- a/04-pizzas.rb
+++ b/04-pizzas.rb
@@ -1,12 +1,14 @@
 # 题目: 输入有多少片比萨饼和多少人，输出每人可以分到几片，以及剩下几片
 
-print "请输入有多少片比萨饼，然后按 Enter: "
+print '请输入有多少片比萨饼，然后按 Enter: '
 pizzas = gets
 
-print "请输入有多少人要吃，然后按 Enter: "
+print '请输入有多少人要吃，然后按 Enter: '
 people = gets
 
 # .....
+average = pizzas.to_i / people.to_i
+left = pizzas.to_i % people.to_i
 
-puts "每人可分得几片: _________ 片"
-puts "还剩下几片: _________ 片"
\ No newline at end of file
+puts "每人可分得几片: #{average} 片"
+puts "还剩下几片: #{left} 片"
diff --git a/05-bmi.rb b/05-bmi.rb
index 67efdff..24efe3a 100644
--- a/05-bmi.rb
+++ b/05-bmi.rb
@@ -4,14 +4,21 @@
 # 如果 BMI >= 24，显示过重
 # 如果 BMI 介于 18.5 ~ 24，显示正常
 
-print "请输入您的体重(公斤)，然后按 Enter: "
+print '请输入您的体重(公斤)，然后按 Enter: '
 weight = gets
 
-print "请输入您的身高(厘米)，然后按 Enter: "
+print '请输入您的身高(厘米)，然后按 Enter: '
 height = gets
 
 # .....
+bmi = weight.to_f / (height.to_f * 0.01)**2
 
-puts "您的 BMI 是: _________"
+puts "您的 BMI 是: #{bmi.round(2)}"
 
-puts "您的 BMI 结果是: _________(过轻或正常或过重)"
\ No newline at end of file
+if bmi < 18.5
+  puts '您的 BMI 结果是: 过轻'
+elsif bmi >= 24
+  puts '您的 BMI 结果是: 过重'
+else
+  puts '您的 BMI 结果是: 正常'
+end
diff --git a/06-interger-positive.rb b/06-interger-positive.rb
index a240f5f..e5b64c6 100644
--- a/06-interger-positive.rb
+++ b/06-interger-positive.rb
@@ -1,10 +1,21 @@
 # 题目: 输入一个数字 x，请判断是否正数、零或负数，以及是不是偶数
 
-
-print "请输入一个整数，然后按 Enter: "
+print '请输入一个整数，然后按 Enter: '
 x = gets
 
 # ....
 
-puts "这个数是_____ (正数或零或负数)"
-puts "这个数是_____ (偶数或奇数)"
\ No newline at end of file
+(
+if x.to_i > 0
+  puts '这个数是正数'
+  if x.to_i.even?
+    puts '这个数是偶数'
+  else
+    puts '这个数是奇数'
+  end
+elsif x.to_i == 0
+  puts '这个数是零'
+else
+  puts '这个数是负数'
+end
+)
diff --git a/07-abcde.rb b/07-abcde.rb
index 5d0c8c3..8c244ff 100644
--- a/07-abcde.rb
+++ b/07-abcde.rb
@@ -8,15 +8,28 @@
 #     当 z > 0 输出 "D"
 #     当 z < 0 输出 "E"
 
-print "请输入一个整数x，然后按 Enter: "
+print '请输入一个整数x，然后按 Enter: '
 x = gets
 
-print "请输入一个整数y，然后按 Enter: "
+print '请输入一个整数y，然后按 Enter: '
 y = gets
 
-print "请输入一个整数z，然后按 Enter: "
+print '请输入一个整数z，然后按 Enter: '
 z = gets
 
 # ....
+if x.to_i < 0
+  puts 'A'
+else
+  if (x.to_i > 0) && (y.to_i > 0) && (z.to_i > 0)
+    puts 'B'
+  elsif (x.to_i > 0) && (y.to_i > 0) && z.to_i < 0
+    puts 'C'
+  else
+    puts 'D' if (y.to_i < 0) && (z.to_i > 0)
+    puts 'E' if (y.to_i < 0) && (z.to_i < 0)
 
-puts "结果是________(A或B或C或D或E)"
\ No newline at end of file
+end
+
+  puts '0' if x.to_i == 0
+end
diff --git a/08-find-max.rb b/08-find-max.rb
index 9e6e643..f2c16b9 100644
--- a/08-find-max.rb
+++ b/08-find-max.rb
@@ -1,14 +1,30 @@
 # 题目: 使用者输入 x,y,z，请输出三个数中最大的数
 
-print "请输入一个数字x，然后按 Enter: "
-x = gets
+print '请输入一个数字x，然后按 Enter: '
+x = gets.to_i
 
-print "请输入一个数字y，然后按 Enter: "
-y = gets
+print '请输入一个数字y，然后按 Enter: '
+y = gets.to_i
 
-print "请输入一个数字z，然后按 Enter: "
-z = gets
+print '请输入一个数字z，然后按 Enter: '
+z = gets.to_i
 
 # ....
+#
+# if a <= 0 && b >= 0
+#   puts '最大的数是y'
+# elsif  a >= 0 &&  c >= 0
+#   puts '最大的数是 x'
+# else
+#   puts '最大的数是z'
+# end
 
-puts "最大的数是 ________(x或y或z)"
\ No newline at end of file
+if x >= y && x >= z
+  puts '最大的数是 x'
+
+elsif y >= x && y >= z
+  puts '最大的数是y'
+else
+  puts '最大的数是z'
+
+end
diff --git a/09-function.rb b/09-function.rb
index b1f922d..2be399b 100644
--- a/09-function.rb
+++ b/09-function.rb
@@ -1,15 +1,15 @@
 # 题目: 输入直角三角形的宽和高，输出三角形的面积
 
 def calculate_area(a, b)
-  # ....
+  (a * b) / 2
 end
 
-print "请输入直角三角形的高，然后按 Enter: "
-a = gets
+print '请输入直角三角形的高，然后按 Enter: '
+a = gets.to_f
 
-print "请输入直角三角形的底边，然后按 Enter: "
-b = gets
+print '请输入直角三角形的底边，然后按 Enter: '
+b = gets.to_f
 
-answer = calculate_area(a,b)
+answer = calculate_area(a, b)
 
-puts "直角三角形的面积是: #{answer}"
\ No newline at end of file
+puts "直角三角形的面积是: #{answer}"
diff --git a/10-function.rb b/10-function.rb
index bb450fb..f0d7d17 100644
--- a/10-function.rb
+++ b/10-function.rb
@@ -1,19 +1,26 @@
 # 题目: 使用者输入 x,y,z，请输出三个数中最大的数
 
 def find_max(x, y, z)
+  if x >= y && x >= z
+    'x'
+  elsif y >= x && y >= z
+    'y'
+  else
+    'z'
+  end
 end
 
-print "请输入一个数字x，然后按 Enter: "
-x = gets
+print '请输入一个数字x，然后按 Enter: '
+x = gets.to_f
 
-print "请输入一个数字y，然后按 Enter: "
-y = gets
+print '请输入一个数字y，然后按 Enter: '
+y = gets.to_f
 
-print "请输入一个数字z，然后按 Enter: "
-z = gets
+print '请输入一个数字z，然后按 Enter: '
+z = gets.to_f
 
 # ....
 
-answer = find_max(x,y,z)
+answer = find_max(x, y, z)
 
-puts "最大的数是 #{answer}"
\ No newline at end of file
+puts "最大的数是 #{answer}"
diff --git a/11-seven.rb b/11-seven.rb
index 26c221d..be4a0b8 100644
--- a/11-seven.rb
+++ b/11-seven.rb
@@ -1,9 +1,7 @@
 # 题目: 列出 1 到 100 之间，所有 7 的倍数
 
 i = 1
-while ( i <= 100 )
-
-  # ....
-
-  i+=1
-end
\ No newline at end of file
+while i <= 100
+  puts i if i % 7 == 0
+  i += 1
+end
diff --git a/12-sum-even.rb b/12-sum-even.rb
index 73879bb..ac8eed4 100644
--- a/12-sum-even.rb
+++ b/12-sum-even.rb
@@ -3,11 +3,9 @@
 i = 1
 total = 0
 
-while ( i <= 100 )
-
-  # ....
-
-  i+=1
+while i <= 100
+  total += i if i.even?
+  i += 1
 end
 
-puts total
\ No newline at end of file
+puts total
diff --git a/13-nn.rb b/13-nn.rb
index ac0a43b..aa6529c 100644
--- a/13-nn.rb
+++ b/13-nn.rb
@@ -1,11 +1,16 @@
 # 题目: 输入一个数字 N，输出 N * N 乘法表
 
-print "请输入数字 N，然后按 Enter: "
-n = gets
-
-# while ( ... )
-#   while ( ...)
-#
-#   end
-# end
+print '请输入数字 N，然后按 Enter: '
+n = gets.to_i
 
+x = 0
+y = 0
+while x <= n
+  while y <= n
+    nn = x.to_i * y.to_i
+    puts "#{x} *  #{y} = #{nn}"
+    y += 1
+  end
+  x += 1
+  y = 0
+end
diff --git a/14-prime.rb b/14-prime.rb
index 8cf1692..9d342d4 100644
--- a/14-prime.rb
+++ b/14-prime.rb
@@ -1,14 +1,19 @@
 # 输入一个数字 N，请检查是不是质数
 
 def is_prime(n)
-# ....
+  x = 2
+  while x <= (n / 2)
+    return false if n % x == 0
+    x += 1
+    end
+  true
 end
 
-print "请输入数字 N，然后按 Enter: "
-n = gets
+print '请输入数字 N，然后按 Enter: '
+n = gets.to_f
 
 if is_prime(n.to_i)
-  puts "这是质数"
+  puts '这是质数'
 else
-  puts "这不是质数"
+  puts '这不是质数'
 end
diff --git a/15-guess-number.rb b/15-guess-number.rb
index 48f9dca..9f3ba59 100644
--- a/15-guess-number.rb
+++ b/15-guess-number.rb
@@ -2,16 +2,21 @@
 
 target = rand(100)
 
-while (true)
-  print "请猜一个 0~99 的数字 N，然后按 Enter: "
-  n = gets
-
-  #puts "太低了，再猜一次"
-  #puts "太高了，再猜一次"
+loop do
+  print '请猜一个 0~99 的数字 N，然后按 Enter: '
+  n = gets.to_i
+  # if n > target
+  #   puts '太高了，再猜一次'
+  # elsif n < target
+  #   puts '太低了，再猜一次'
+  # end
 
   if n.to_i == target
-    puts "恭喜猜中啦! "
+    puts '恭喜猜中啦! '
     break
+  elsif n > target
+    puts '太高了，再猜一次'
+  else
+    puts '太低了，再猜一次'
   end
-
-end
\ No newline at end of file
+end
diff --git a/16-array-sum.rb b/16-array-sum.rb
index 9b4910b..4cf3456 100644
--- a/16-array-sum.rb
+++ b/16-array-sum.rb
@@ -1,11 +1,13 @@
 # 给定一阵列内含数字，输出最大值
 
 def find_max(array)
-  #....
+  x = 0
+  for i in array
+    x = i if x < i
+  end
+  x
 end
-
 arr = [8, 12, 36, 53, 9, 75, 3, 71, 59, 88]
 
 max = find_max(arr)
 puts "Max is #{max}" # 应该是 88
-
diff --git a/17-array-stats.rb b/17-array-stats.rb
index 0af81bb..3c0f94c 100644
--- a/17-array-stats.rb
+++ b/17-array-stats.rb
@@ -2,8 +2,8 @@
 
 arr = []
 
-while (true)
-  print "请输入数字，结束请直接按 Enter: "
+loop do
+  print '请输入数字，结束请直接按 Enter: '
   user_input = gets
   if user_input == "\n"
     break
@@ -14,7 +14,20 @@
 
 puts arr.to_s
 
-puts "总和是 _____"
-puts "平均是 _____"
-puts "最大值是 _____"
-puts "最小值是 _____"
\ No newline at end of file
+def sum(array)
+  x = 0
+  array.each do |i|
+    x += i
+  end
+  x
+end
+
+def average(array)
+  a = sum(array)
+  a / array.size
+end
+
+puts "总和是 #{sum(arr)} "
+puts "平均是 #{average(arr)}"
+puts "最大值是 #{arr.max}"
+puts "最小值是 #{arr.min}"
diff --git a/18-square.rb b/18-square.rb
index 226e1c1..2e34fa4 100644
--- a/18-square.rb
+++ b/18-square.rb
@@ -2,9 +2,13 @@
 
 arr = []
 
-print "请输入数字 N，然后按 Enter: "
-n = gets
+print '请输入数字 N，然后按 Enter: '
+n = gets.to_i
+x = 0
 
-# ...
+while x <= n - 1
+  arr.push(x**2)
+  x += 1
+end
 
-puts arr.to_s
\ No newline at end of file
+puts arr.to_s
diff --git a/19-filter.rb b/19-filter.rb
index ef7e515..738eb71 100644
--- a/19-filter.rb
+++ b/19-filter.rb
@@ -1,9 +1,13 @@
 # 给定一阵列内含数字，输出另一个数组只包含偶数
 
 def filter_even(arr)
-  #...
+  arreven = []
+  arr.each do |i|
+    arreven.push(i) if i.even?
+  end
+  arreven
 end
 
-arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
+arr = [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
 
-puts filter_even(arr).to_s # 应该是 [68, 42, 46, 46, 86]
\ No newline at end of file
+puts filter_even(arr).to_s # 应该是 [68, 42, 46, 46, 86]
diff --git a/20-sorting.rb b/20-sorting.rb
index 5f82c08..5a64a45 100644
--- a/20-sorting.rb
+++ b/20-sorting.rb
@@ -2,10 +2,15 @@
 # Hint: 可用 arr.sort 排序，和 arr.uniq 去除重复
 
 def filter_even(arr)
-  #...
-end
+  arreven = []
+  arr.each do |i|
+    arreven.push(i) if i.even?
+  end
 
-arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
+  # arreven.sort.uniq
+  arreven.uniq.sort
+end
 
+arr = [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
 
-puts "________" # 应该是 [42, 46, 68, 86]
\ No newline at end of file
+puts filter_even(arr).to_s # 应该是 [42, 46, 68, 86]
diff --git a/21-selection-sort.rb b/21-selection-sort.rb
index e5e7eae..6c4ca13 100644
--- a/21-selection-sort.rb
+++ b/21-selection-sort.rb
@@ -1,12 +1,34 @@
 # 给定一数组内含数字，请实作选择排序法进行排序。
 # https://zh.wikipedia.org/wiki/选择排序
 
+# def selection_sort(arr)
+#   (0..arr.size - 1).each do |i|
+#     min = arr[i]
+#     k = i
+#     (i + 1..arr.size - 1).each do |j|
+#       if arr[j] < min
+#         min = arr[j]
+#         k = j
+#       end
+#     end
+#     arr[k] = arr[i]
+#     arr[i] = min
+#   end
+#   arr
+# end
+
 def selection_sort(arr)
-  #...
+  sorted = []
+  arr.size.times do |_i|
+    min = arr.min
+    sorted << min
+    arr.delete_at(arr.index(min))
+  end
+  sorted
 end
 
 arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
 
 answer = selection_sort(arr)
 
-puts answer.to_s # 应该是 [1, 7, 9, 42, 46, 46, 68, 77, 86, 91]
\ No newline at end of file
+puts answer.to_s # 应该是 [1, 7, 9, 42, 46, 46, 68, 77, 86, 91]
diff --git a/22-missing.rb b/22-missing.rb
index 6898714..45f69ff 100644
--- a/22-missing.rb
+++ b/22-missing.rb
@@ -1,9 +1,17 @@
 # 给定一阵列内含数字，请输出 0~9 中不见的数字
 
+# def find_missing(arr)
+#   missing = []
+#   (0..9).each do |i|
+#     missing << i unless arr.include?(i)
+#   end
+#   missing
+# end
+
 def find_missing(arr)
-  # ...
+  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] - arr.uniq.sort
 end
 
-answer = find_missing( [2,2,1,5,8,4] )
+answer = find_missing([2, 2, 1, 5, 8, 4])
 
 puts answer.to_s # 应该是 [0,3,6,7,9]
diff --git a/23-hash-max.rb b/23-hash-max.rb
index 6fb227e..0141ba7 100644
--- a/23-hash-max.rb
+++ b/23-hash-max.rb
@@ -1,19 +1,17 @@
 # 给定一 Hash，输出有最大 value 的 key
 
 def find_max(hash)
-  # ...
+  hash.max_by { |_k, v| v }
 end
 
 h = {
-  "a" => 71,
-  "b" => 38,
-  "c" => 21,
-  "d" => 80,
-  "e" => 10
+  'a' => 71,
+  'b' => 38,
+  'c' => 21,
+  'd' => 80,
+  'e' => 10
 }
 
 answer = find_max(h)
 
 puts "有最大 value 的是 #{answer}" # 应该是 d
-
-
diff --git a/24-hash-even.rb b/24-hash-even.rb
index 9da9605..74538ea 100644
--- a/24-hash-even.rb
+++ b/24-hash-even.rb
@@ -1,21 +1,26 @@
 # 给定一 Hash，输出 value 是偶数的 keys
 
 def find_even_keys(hash)
-
-  # ... (请回传一个数组)
-
+  even = []
+  hash.values.each do |v|
+    even << hash.key(v) if v.even?
+  end
+  # arr = []
+  # even.each do |k|
+  #   arr << hash.key(k)
+  # end
+  # arr
+  even
 end
 
 h = {
-  "a" => 71,
-  "b" => 38,
-  "c" => 21,
-  "d" => 80,
-  "e" => 10
+  'a' => 71,
+  'b' => 38,
+  'c' => 21,
+  'd' => 80,
+  'e' => 10
 }
 
 answer = find_even_keys(h)
 
 puts "有偶数 value 的 keys 有 #{answer}" # 应该是数组 [b,d,e]
-
-
diff --git a/25-hash-count.rb b/25-hash-count.rb
index 2167335..e335897 100644
--- a/25-hash-count.rb
+++ b/25-hash-count.rb
@@ -4,15 +4,14 @@ def count(arr)
   h = {}
 
   arr.each do |i|
-    # ...
+    h[i] = arr.count(i)
   end
 
-  return h # 回传一个 hash
+  h # 回传一个 hash
 end
 
-arr =  ["a", "d", "d", "c", "b", "c", "c", "c", "d", "d", "e", "e", "e", "d", "a", "c", "e", "a", "d", "e"]
+arr =  %w[a d d c b c c c d d e e e d a c e a d e]
 
 answer = count(arr)
 
 puts answer # 答案应该是 {"a"=>3, "d"=>6, "c"=>5, "b"=>1, "e"=>5}
-
diff --git a/26-hash-filter.rb b/26-hash-filter.rb
index 51ade64..37c65ba 100644
--- a/26-hash-filter.rb
+++ b/26-hash-filter.rb
@@ -1,20 +1,23 @@
 # 给定一个数组包含 Hash，请过滤和排序
 
 arr = [
-  { "name" => "Peter", "age" => 30 },
-  { "name" => "John", "age" => 15 },
-  { "name" => "David", "age" => 45 },
-  { "name" => "Steven", "age" => 22 },
-  { "name" => "Vincent", "age" => 6 },
+  { 'name' => 'Peter', 'age' => 30 },
+  { 'name' => 'John', 'age' => 15 },
+  { 'name' => 'David', 'age' => 45 },
+  { 'name' => 'Steven', 'age' => 22 },
+  { 'name' => 'Vincent', 'age' => 6 }
 ]
 
-# ....
-
-puts "所有成年人，并由小到大: _________"
+answer = []
+arr.each do |i|
+  answer.push(i) if i['age'] >= 18
+end
+answer.sort_by { |k| k['age'] }
+puts "所有成年人，并由小到大: #{answer}"
 
 # 答案应该是
-#[
+# [
 #  { "name" => "Steven", "age" => 22 },
 #  { "name" => "Peter", "age" => 30 },
 #  { "name" => "David", "age" => 45 }
-#]
+# ]
diff --git a/27-class.rb b/27-class.rb
index 8cec2c9..5459ced 100644
--- a/27-class.rb
+++ b/27-class.rb
@@ -1,16 +1,18 @@
 class Person
-  # ...
+  attr_accessor :first_name, :last_name
+  def greet
+    "Hello, #{@first_name} #{@last_name}"
+  end
 end
 
 p1 = Person.new
-p1.first_name = "Peter"
-p1.last_name = "Wang"
+p1.first_name = 'Peter'
+p1.last_name = 'Wang'
 p1.greet # 输出 "Hello, Peter Wang"
 
 p2 = Person.new
-p2.first_name = "William"
-p2.last_name = "Zhang"
+p2.first_name = 'William'
+p2.last_name = 'Zhang'
 p2.greet # 输出 "Hello, William Zhang"
 
-
-
+# https://stackoverflow.com/questions/4370960/what-is-attr-accessor-in-ruby
diff --git a/28-word-count.rb b/28-word-count.rb
index 2643123..18b74b1 100644
--- a/28-word-count.rb
+++ b/28-word-count.rb
@@ -1,5 +1,16 @@
 # 请打开 wordcount.txt，计算每个单字出现的次数
 
-doc = File.read("wordcount.txt")
+doc = File.read('wordcount.txt')
+# word = doc.split(/\r\n|\n/)
+word = doc.downcase.gsub(/(n['’]t\b)|\p{P}/, '\1').split(/\s+/).reject(&:empty?)
+def count(word)
+  h = {}
+  word.each do |i|
+    h[i] = word.count(i)
+  end
+  h # 回传一个 hash
+end
 
-# ...
+answer = count(word).sort
+
+puts answer
diff --git a/29-todos.rb b/29-todos.rb
index 0bddde2..23c2ae6 100644
--- a/29-todos.rb
+++ b/29-todos.rb
@@ -1,6 +1,6 @@
 # 简易 Todo 代办事项应用
 
-text = File.read("todos.txt")
+text = File.read('todos.txt')
 
 todos = []
 text.each_line do |line|
@@ -11,23 +11,36 @@
   puts "#{index}: #{todo}"
 end
 
-while (true)
-  print "请输入指令 1. add 2. remove 3. save，然后按 Enter: "
+loop do
+  print '请输入指令 1. add 2. remove 3. save，然后按 Enter: '
   command = gets.chomp
 
-  if command == "add"
-    print "请输入代办事项: "
-    # ...
-  elsif command == "remove"
-    print "请输入要删除的编号: "
-    # ...
-  elsif command == "save"
-    puts "存盘离开"
+  if command == 'add'
+    print '请输入代办事项: '
+    add = gets.chomp
+    todos << add
+    todos.each_with_index do |todo, index|
+      puts "#{index}: #{todo}"
+    end
 
-    # ...
-    break;
+  elsif command == 'remove'
+    print '请输入要删除的编号: '
+    remove = gets.to_i
+    todos.delete_at(remove)
+    todos.each_with_index do |todo, index|
+      puts "#{index}: #{todo}"
+    end
+
+  elsif command == 'save'
+    puts '存盘离开'
+    File.open('todos.txt', 'w+') do |f|
+      todos.each do |i|
+        f << i
+        f << "\n"
+      end
+    end
+    break
   else
-    puts "看不懂，请再输入一次"
+    puts '看不懂，请再输入一次'
   end
 end
-
diff --git a/todos.txt b/todos.txt
index 4757e85..d27e96f 100644
--- a/todos.txt
+++ b/todos.txt
@@ -2,3 +2,6 @@ Buy book
 Go Shopping
 Walk
 Gogo
+3333
+4444
+23456