Ruby-String.to_i错误

写一个年龄检查器程序，我正在添加代码来检查输入错误

我在理解一段代码的问题时遇到了一个问题，ruby为传递到一些字符串对象中的.to_I方法返回一个（NoMethodError）

完整代码如下

def calculate_difference(year,month,day)
  years = Time.new.year - year
  months = Time.new.month - month
  days = Time.new.day - day 
  if months == 0
    if days < 0
        age = years - 1
    elsif days >= 0
        age = years
    end
  elsif months > 0
    age = years
  else
    age = years - 1
  end
end

puts "What year were you born in?"
year = gets.chomp
while year.to_i < 1900 or year.to_i > Time.new.year - 5
  puts "Please enter a year between 1900 and 5 years ago"
  year = gets.chomp
end
puts "And the month?"
month = gets.chomp
while month.to_i > 12 or month.to_i <= 0
  puts "MONTH please, numbers from 1 to 12..."
  month = gets.chomp
end
puts "And the day number?"
day = gets.chomp

我不确定它为什么会抛出错误，因为我确定字符串整数会响应.to_I方法

“

=

”是分配。 “

==

”正在检查它们是否相等，并返回true或false

if month.to_i == 1 or month.to_i == 3 or month.to_i == 5 or month.to_i == 7 or month.to_i == 8 or month.to_i == 10 or month.to_i == 12
  while day.to_i > 31 or day.to_i <= 0
  puts "Your month of birth has 31 days, please select a date within the correct range"
  day = gets.chomp
  end
end
if month.to_i == 2
  while day.to_i > 28 or day.to_i < 0
    puts "Incorrect day selected for February"
    day = gets.chomp
  end
end

如果month.to_i==1或month.to_i==3或month.to_i==5或month.to_i==7或month.to_i==8或month.to_i==10或month.to_i==12
而day.to_i>31或day.to_i 28或day.to_i<0
将“为二月选择的日期不正确”
day=get.chomp
结束
结束

或更具可读性：

if [1, 3, 5, 7, 8, 10, 12].include? month.to_i
  while day.to_i > 31 or day.to_i <= 0
    puts "Your month of birth has 31 days, please select a date within the correct range"
    day = gets.chomp
  end
end
if 2 == month.to_i
  while day.to_i > 28 or day.to_i < 0
    puts "Incorrect day selected for February"
    day = gets.chomp
  end
end

if[1,3,5,7,8,10,12]。是否包括？月至月
而day.to_i>31或day.to_i 28或day.to_i<0
将“为二月选择的日期不正确”
day=get.chomp
结束
结束

错误消息的内容是“未定义方法”

到_i=

”，而不是“

到_i

”

这是因为Ruby将单个“=”解释为您想要调用假设字段

上的setter方法，以_i

：

a = "12"
a.to_i == 12
# returns true

a.to_i = 12
# throws undefined method to_i= 

12 = a.to_i
# creates a syntax error with the better message "unexpected ="
# prevents such assigns-equals errors
12 == a.to_i
# returns true

---

当您应该使用

=

扩展@Ajedi32编写的内容时，您正在使用

=

：双等号

=

是相等运算符，用于确定两个值是否相等；这就是你想要的。单个equals

=

是赋值运算符，用于将右侧的值赋值给左侧的变量。（有关最后一部分的更多信息，请参阅）扩展@iamnotmaynard所写的内容：所有条件都应写为

const value equal variable

，这意味着所有

lvalue

项都不能

意外地指定新值
item==0
bad choice，但是
0==item
好多了注意，谢谢你的帮助这个答案只解释错误，不教或防止将来的错误抱歉我最近看到并修改了这个，很快会回来更新。谢谢大家的帮助，@bisounours tronconneuse谢谢你的提示这看起来更干净，可以用这种方式实现。正是@gaussblurinc建议了这种更可读的格式，并用这种格式编辑了我的答案，所以你应该感谢他；）我明白了，谢谢你！谢谢，这很有道理
if [1, 3, 5, 7, 8, 10, 12].include? month.to_i
  while day.to_i > 31 or day.to_i <= 0
    puts "Your month of birth has 31 days, please select a date within the correct range"
    day = gets.chomp
  end
end
if 2 == month.to_i
  while day.to_i > 28 or day.to_i < 0
    puts "Incorrect day selected for February"
    day = gets.chomp
  end
end

a = "12"
a.to_i == 12
# returns true

a.to_i = 12
# throws undefined method to_i= 

12 = a.to_i
# creates a syntax error with the better message "unexpected ="
# prevents such assigns-equals errors
12 == a.to_i
# returns true