Ruby programming error (undefined local variable)

Question

I tried to make a credit card payment calculator. 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

I'm getting an error message:

'calc_payment': undefined local variable or method 'payment' for main:Object (NameError)

Answer 1

Your issue revolves around variable scope. payment has a local scope, and therefore the function calc_payment cannot "see" it. Here I modified your program so that you pass payment, balance, and apr into the calc_payment function. I also moved m_counter into the function as well.

def calc_payment(payment, balance, apr)
  m_counter = 0
  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(payment, balance, apr)