1. Flow Control II
While Loops

2. Greeter Revisited
name = input("What's your name?") if name != "": print('Hello,', name, '!') else: print("You didn't enter a name!") This program handles missing input, but... We want to give a user who fails to enter a name another chance!

3. A Second Chance... ?!
name = input("What's your name?") if name != "": print('Hello,', name, '!') else: print("You didn't enter a name!")
Coding Horror

4. Looping Revisited
You know how to repeat a section of code a set number of times
Sometimes, you need a way to repeat a section of code as long as a condition holds
The while loop repeats a section of code until its condition becomes false:
print("Countdown:")
num = 5
while num > 0:
print(num, '...')
num = num - 1
print("Blast off!")
Countdown: 5 4 3 2 1
Blast off!

5. Can We Use a While Loop?
name = input("What's your name?") if name != "": print('Hello,', name, '!') else: print("You didn't enter a name!") Challenge: Rewrite this program using a while loop so the user gets repeated chances to enter a name.

6. Requiring a Valid Entry
name = input("What's your name?") while name == "": print("You didn't enter a name!") print('Hello,', name, '!')

7. The Formatter We're writing a program to format the user's hard drive
Before we do the deed, we want the user to confirm:
confirm = input("Should I format your hard drive (Y/N)?")
if confirm == 'Y':
print('Formatting drive...')
elif confirm == 'N':
print('We won't format your drive.')
else:
print('Invalid entry.')
Challenge: Require the user to enter a Y or N, prompting repeatedly until they do so.
For those who know about Boolean logic, do it without Boolean operators

8. Requiring a Valid Entry II
valid = False while valid == False: confirm = input("Should I format your hard drive (Y/N)?") if confirm == 'Y': valid = True elif confirm == 'N': else: print('I didn't understand your response. Please enter Y or N.')