# average3.py
# From Zelle textbook p240
#
# Average numbers using a sentinal loop (a while loop with a sentinal)
#   The sentinal must be some item not in the input set
#   Negative numbers can't be averaged in this program

def main():

  sum = 0.0
  count = 0

  x = input("Enter a number (-1 to quit): ")      # priming the loop
  while x >= 0:
    sum = sum + x
    count = count + 1
    x = input("Enter a number (-1 to quit): ")

  print"\nAverage is: ", sum/count


main()