# Program to show interactive while loop
# Matt Bishop, May  4, 2009
# for ECS 10 Spring 2009

# reads a number and makes sure it is a number
# return the sentinel, -9999 on end of file
def readnum():
    # we loop until we find a number
    isnum = "no"
    while isnum == "no":
        # now we read a number, looking for bogus input
        try:
            n = input("Enter number (-9999 to quit): ")
            # this raises an exception if it's not a number
            n += 0
        except EOFError:    # end of file found; quit gracefully
            n = -9999
            isnum = "yes"
        except (NameError, TypeError, SyntaxError):  # non-number entered; complain
            print "You did not enter a number"
        else:   # got a number
            isnum = "yes"
    # once you get a number, return it
    return n
    
# computes an average
def main():
    sum = 0
    count = 0
    # go until user says enough
    n = readnum()
    while n != -9999:
        # add number, increment count
        sum += n;
        count += 1
        # get next number
        n = readnum()

    # print average
    if (count > 0):
        print "The average of the", count, "numbers you entered is", float(sum)/count
    else:
        print "No numbers entered!"

main()