“+”串不能强迫Fixnum对象（类型错误）

Question

这是一个简单的计算公式，即时通讯做尝试首次红宝石和停留在一个简单的错误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 

错误时我计算式I最终得到此[主未定义的方法率：对象（NoMethodError）]

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

puts "#{monthly_payment}" 

Answer 1

有一个叫Exonio宝石：https://github.com/Noverde/exonio。 这个宝石实现了一些Excel的财务方法，如：PMT，IPMT，PV，NPER ...

Answer 2

方法gets总是返回字符串

loan_amount = gets 
=> "1" 

您应该计算之前字符串转换为数字：

loan_amount = gets 
loan_amount = loan_amount.to_f 
...