Answer to Question #237960 in Python for Joel

Question

Write a Python program that gets a number using keyboard input. (Remember to use input for Python 3 but raw_input for Python 2.)

If the number is positive, the program should call countdown. If the number is negative, the program should call countup. Choose for yourself which function to call (countdown or countup) for input of zero.

Provide the following.

• The code of your program.
• Output for the following input: a positive number, a negative number, and zero.
• An explanation of your choice for what to call for input of zero.

Answer 1

import sys

# count down function
def countdown(n):
  if n <= 0:
    print('Blastoff!')
  else:
    print(n)
    countdown(n-1)

# count up function
def countup(n):
  if n >= 0:
    print('Blastoff!')
  else:
    print(n)
    countup(n+1)

# ask user to enter number 
if sys.version_info[0] == 3:
  num = input('Enter number: ')
else:
  num = raw_input('Enter number: ')

# convert string to number
num = int(num)

if num > 0:
  # count down positive number
  countdown(num)
elif num < 0:
  # count up negative number
  countup(num)
else:
  # there is no difference which function to call
  # in case of 0, both functions will print 'Blastoff!'
  print('Blastoff!')

# Outputs:
# num=3    3 2 1 Blastoff!
# num=-3   -3 -2 -1 Blastoff!
# num=0    Blastoff!