"""File:     avg_var.py
   Purpose:  Find the average, variance, and standard deviation of a 
             collection of user input numbers

   Run:      python avg_py.py

   Input:    A sequence of numbers, one per line of input, 0 terminates
             input
   Output:   The average, variance, and standard deviation of the numbers
"""
from math import sqrt

sum = 0.0
sum_sq = 0.0
count = 0
number = float(raw_input("Enter the first number (0 to quit)\n"))
while number != 0:
   sum = sum + number
   sum_sq = sum_sq + number*number
   count = count + 1
   number = float(raw_input("Enter the next number (0 to quit)\n"))

if count > 0:
   avg = sum/count
   print "The average of the input values is", avg
else:
   print "You didn't enter any nonzero numbers!"

if count > 1:
   variance = (sum_sq - count*avg*avg)/(count-1)
   std_dev = sqrt(variance)
   print "variance =", variance
   print "std deviation =", std_dev
else:  
   print "For variance you need at least two numbers"