Investigate

This investigation will help you learn how to make a while loop, so that you can repeat a section of instructions over and over again.

Type the following code into WingIDE and run it:

password = "scuba"

print ("Welcome to The Bank!")

print ("For your financial safety, please enter your password to verify your identity")

print ("")

entry = raw_input("Enter your password: ")

while (password != entry):

    print ("Incorrect. Please try again.")

    print ("")

    entry = raw_input("Enter your password: ")

print ("")

print ("Identity Verified. Thank you. You may now complete your banking.")

In the above code, we use a while loop to ensure that the user enters the correct password before we continue.

Answer the following questions and hand them in.

1. How is a while loop similar to an if statement?
2. How is a while loop different from an if statement?
3. What happens if you enter the password in correctly after the first try?
4. Inside the while loop, what is happening on the line entry = raw_input("Enter your password: ")?
5. Delete the line entry = raw_input("Enter your password: ") from inside the while loop. What happens? Why?

Modify

Copy the following code into WingIDE and make the changes listed below:

import random

value = random.randint(1, 100)

print("Pick-A-Number")

print("Your computer has chosen a number between 1 and 100. It's your job to find it!")

print("")

guess = int(raw_input("Choose a Number: "))

if (guess < value):

    print("Aww... Too low. Better luck next time!")

elif(guess > value):

    print("A bit too high! Too bad.")

else:

    print("Bingo! You got it. The number was " + str(value))

Changes:

• Use a while loop to allow the users to guess as many times as necessary for them to correctly guess the number.
• Count the number of guesses and output the information to the user after they guess the correct number. (If you can't figure this one out, look ahead to investigate 2)

Try It Out

1. Write a program that simulates a dice roll by picking a random number from 1-6 and then picking a second random number from 1-6. Add the two values together, and display the total. The program should continue to do this until the computer rolls doubles (the same value on both dice).

Note that there is no user input here. So it should happen very quickly.

Investigate 2

We don't always have to base our exits on user input. Sometimes we can base it off of an internal counter. Type the following code into WingIDE and run it:

print("Repeater")

print("Type in a message and I'll repeat it 5 times")

message = raw_input("Message: ")

print("")

counter = 0

while (counter < 5):

    print (str(counter + 1) + ". " + message)

    counter += 1

Normally, while loops are best for repeating as long as something is true:

• Keep going as long as they haven't guessed it.
• Keep going as long as you haven't got doubles.
• Keep going as long as they keep typing in a negative number.
• Keep going as long as they haven't typed in a zero.

But sometimes, we know in advance how many times we want to do something.

• Do this ten times.
• Do this five times.
• Pick a random number, and do it that many times.
• Take this list of items, and do it one time for each item in the list.

We can do that sort of thing with a while loop, but we have to use a counter. A counter is a number variable (int or double) that starts with a value of 0, and then we add 1 to it whenever something happens. So, here, we're going to be adding 1 to the counter every time we repeat the loop. And when the counter reaches a predetermined value, we'll stop looping.

Answer the following questions and hand them in.

1. What does counter += 1 do? Remove it and see what happens. (Then put it back.)
2. How would you change the code so that the loop repeats ten times instead of five. (Verify that you are correct)

Modify

Using the previous code, try to make the following changes:

1. Change the code so that the message still prints five (or ten) times, but the numbers in front count by tens, like so:

Repeater

Type in a message and I'll repeat it 5 times

Message: I didn't do it!

10. I didn't do it!

20. I didn't do it!

30. I didn't do it!

40. I didn't do it!

50. I didn't do it!

2. Change the code so that it asks the person how many times to display the message. Then, print it that many times. Still count by tens.

Repeater

Type in a message and I'll repeat it many times

Message: *Knock, Knock, Knock* Penny?

How many times? 3

10. *Knock, Knock, Knock* Penny?

20. *Knock, Knock, Knock* Penny?

30. *Knock, Knock, Knock* Penny?

Try It Out

Write a program that uses a while loop gets several integers from the user. Sum up all the integers they give you. Stop looping when they enter a 0. Display the total at the end. Here is some sample input/output:

I will add up the numbers you give me.

Number: 6

The total so far is 6

Number: 9

The total so far is 15

Number: -3

The total so far is 12

Number: 2

The total so far is 14

Number: 0

The total is 14.

I will add up the numbers you give me.

Number: 1

The total so far is 1

Number: 2

The total so far is 3

Number: 3

The total so far is 6

Number: 4

The total so far is 10

Number: 5

The total so far is 15

Number: 0

The total is 15