ruby - '+' 字符串不能被强制转换为 Fixnum (TypeError)

Question

这是一个简单的计算公式，我第一次尝试 ruby​​ 并遇到一个简单的错误 bt 需要一些指导

#input
loan_amount = 0
rate = 0
period = 0

#output
monthly_payment = 0

print "Enter loan_amount: "
loan_amount = gets.to_f
print "Enter rate: "
rate = gets.to_f
print "Enter period: "
period = gets.to_f

当我计算公式时出错，我最终得到了这个 [main:Object (NoMethodError) 的未定义方法率]

monthly_payment = loan_amount((rate(1 + rate)**period)/(1 + rate)**period - 1)

puts "#{monthly_payment}"

Answer 1

方法gets总是返回字符串

loan_amount = gets
=> "1"

您应该在计算之前将字符串转换为数字：

loan_amount = gets
loan_amount = loan_amount.to_f
...

Answer 2

有一个叫做 Exonio 的 gem：https ://github.com/Noverde/exonio 。这个 gem 实现了一些 Excel 财务方法，例如：PMT、IPMT、PV、NPER...