Undefined local variable | Ruby Beginner

ruby-talk
1

I just started learning Ruby a few weeks ago and tried to make a credit
card payment calculator today to practice but I'm getting an error
message: 'calc_payment': undefined local variable or method 'payment'
for main:Object (NameError)

Could someone help me out? As I see it, I defined all the variables so I
don't understand why I'm getting the error message.

Here's the whole code:

m_counter = 0

def calc_payment
  payment_percentage = payment / balance * 100
  monthly_apr = apr / 12

  while balance > 0
   m_counter = m_counter + 1
   balance = balance / 100 * monthly_apr
   balance = balance - payment
  end

  puts
  puts "Monthly payment: $" + payment
  puts "Balance payoff: " + m_counter + " months"

end

puts "Welcome to your credit card payment calculator!"
puts

puts "Please tell me your credit card balance."
balance = gets.chomp.to_f

puts "Please enter your interest rate %."
apr = gets.chomp.to_f

puts "How much $ would you like to pay every month?"
payment = gets.chomp.to_f

calc_payment

···

--
Posted via http://www.ruby-forum.com/.

2

You will need to pass those in as parameters

def calc_payment(payment, balance, apr)
  ...
end

and then call it with

···

On 12 October 2013 15:19, Greg Hajdu <lists@ruby-forum.com> wrote:

I just started learning Ruby a few weeks ago and tried to make a credit
card payment calculator today to practice but I'm getting an error
message: 'calc_payment': undefined local variable or method 'payment'
for main:Object (NameError)

Could someone help me out? As I see it, I defined all the variables so I
don't understand why I'm getting the error message.

Here's the whole code:

m_counter = 0

def calc_payment
  payment_percentage = payment / balance * 100
  monthly_apr = apr / 12

  while balance > 0
   m_counter = m_counter + 1
   balance = balance / 100 * monthly_apr
   balance = balance - payment
  end

  puts
  puts "Monthly payment: $" + payment
  puts "Balance payoff: " + m_counter + " months"

end

puts "Welcome to your credit card payment calculator!"
puts

puts "Please tell me your credit card balance."
balance = gets.chomp.to_f

puts "Please enter your interest rate %."
apr = gets.chomp.to_f

puts "How much $ would you like to pay every month?"
payment = gets.chomp.to_f

calc_payment

--
Posted via http://www.ruby-forum.com/\.

3

Oops mistyped there. You should have something like this

def calc_payment(payment, balance, apr)
  payment_percentage = payment / balance * 100
  monthly_apr = apr / 12

  m_counter = 0
  while balance > 0
   m_counter = m_counter + 1
   balance = balance / 100 * monthly_apr
   balance = balance - payment
  end

  puts
  puts "Monthly payment: $#{payment}"
  puts "Balance payoff: #{m_counter} months"
end

puts "Welcome to your credit card payment calculator!"
puts

puts "Please tell me your credit card balance."
balance = gets.chomp.to_f

puts "Please enter your interest rate %."
apr = gets.chomp.to_f

puts "How much $ would you like to pay every month?"
payment = gets.chomp.to_f

calc_payment(payment, balance, apr)

The points to note is that m_counter is now defined inside the function and
that the printing is done in a more Rubyish way.

However your code still has a problem...

   balance = balance / 100 * monthly_apr
   balance = balance - payment

This will result is in the balance being paid off after a month.

Welcome to your credit card payment calculator!

Please tell me your credit card balance.
1500
Please enter your interest rate %.
12
How much $ would you like to pay every month?
200

Monthly payment: $200.0
Balance payoff: 1 months

4

Thank you for your help!
I modified it and also noticed the problem with the formula.
So this is what I got. It looks like it works, I think there are only
problems with the calculator part. Somehow the results aren't the same
as some online calculators. But as long as the code works, I'm happy. :slight_smile:

def calc_payment(payment, balance, apr)
  m_counter = 0
  total = balance
  payment_percentage = payment / balance * 100
  monthly_apr = apr / 12

  while balance > 0
   m_counter = m_counter.to_i + 1
   month_interest = balance / 100 * monthly_apr
   balance = balance + month_interest
   balance = balance - payment
   total = total + month_interest
  end

  puts
  puts "Monthly payment: $" + payment.to_s
  puts "Balance payoff: " + m_counter.to_s + " months"
  puts "Total payments: $" + total.round(2).to_s

end

puts "Welcome to your credit card payment calculator!"
puts

puts "Please tell me your credit card balance."
balance = gets.chomp.to_f

puts "Please enter your interest rate %."
apr = gets.chomp.to_f

puts "How much $ would you like to pay every month?"
payment = gets.chomp.to_f

calc_payment(payment, balance, apr)

···

--
Posted via http://www.ruby-forum.com/.

5

Thank you for your help!
I modified it and also noticed the problem with the formula.
So this is what I got. It looks like it works, I think there are only
problems with the calculator part. Somehow the results aren't the same
as some online calculators. But as long as the code works, I'm happy. :slight_smile:

Differences might be caused by integer division (just a guess without
going through the calculation in detail):

2.0.0-p247 :001 > 8 / 5
=> 1
2.0.0-p247 :002 > 8.0 / 5
=> 1.6
2.0.0-p247 :003 > 8.to_f / 5
=> 1.6

Regards,
Marcus

def calc_payment(payment, balance, apr)
  m_counter = 0
  total = balance
  payment_percentage = payment / balance * 100
  monthly_apr = apr / 12

[...]

···

Am 12.10.2013 17:11, schrieb Greg Hajdu:

--
GitHub: stomar (Marcus Stollsteimer) · GitHub
PGP: 0x6B3A101A