title: Multiple parameters definition of a function Python
body: <p>I'm trying to write a function that calculates the cost of a loan, but I keep getting the cost of the loan to be the negative value of what the user inputs as the amount of the loan. </p>
  
  <pre><code>#define monthly payment
  def MonthlyPayment (ammountOfLoan, numberOfPeriods,yearlyInterestRate):
      ammountOfLoan = 0
      numberOfPeriods = 0
      yearlyInterestRate = 0
      payment = [(yearlyInterestRate/12)/(1-(1+yearlyInterestRate/12))**(-numberOfPeriods)] * ammountOfLoan      
      return (payment)
  
  
  #define cost of loan    
  def LoanCost(principal, month, payment):
      period = 0
      month = 0
      payment = 0
      cost = period * payment - principal
      return (cost)
  
  #calculate cost of loan
  def main():
      loan = float(raw_input("What is the ammount of your loan? "))
      period = float(raw_input("How many months will you make payments? "))
      rate = float(raw_input("What is the interest rate? "))
      rate = rate / 100
      MonthlyPayment(loan, period, rate)
      costOfLoan = LoanCost(loan, period, rate)
      print "The cost of the loan is $" + str(costOfLoan)
  
  #run main
  main()
  </code></pre>