CS21 Lab 4: while loops and functions

Due Saturday, October 6, before midnight

Make sure all programs are saved to your cs21/labs/04 directory. Files outside this directory will not be graded.

$ update21
$ cd ~/cs21/labs/04/

Programming Tips

• Use a comment at the top of the file to describe the purpose of the program. (Include your name and the date.)
• Use meaningful variable and function names.
• Use comments for each function that include:
  • a description of what the function does
  • a description of the input parameter value(s)
  • a description of the return value
• Write your programs incrementally (a little bit at a time) and test them as you go.
• Don't assume that if your program passes the sample tests we provide that it is completely correct. Come up with your own test cases and verify that the program is producing the right output on them.

Topics for this assignment

• while loops
• functions

1. Guess my Number

Write a program, guess.py, that allows the user to guess a secret number. First use the random module to pick a random (secret) number between 1 and 20 (inclusive). If their guess is below the secret number, print Too low!, and if their guess is above the secret number, print Too high!.

$ python3 guess.py
Enter your guess: 15
Too low!
Enter your guess: 18
Too high!
Enter your guess: 17
Too high!
Enter your guess: 16
You guessed it in 4 guesses!

$ python3 guess.py
Enter your guess: 20
Too high!
Enter your guess: 1
Too low!
Enter your guess: 4
Too low!
Enter your guess: 8
Too low!
Enter your guess: 12
Too high!
Enter your guess: 2
Too low!
Enter your guess: 10
Too low!
Enter your guess: 15
Too high!
Enter your guess: 12
Too high!
Enter your guess: 11
You guessed it in 10 guesses

Hint: define a boolean variable that keeps track of whether or not the secret number has been "guessed". In your while statement, you can use this variable to check whether you should break out of the loop!

Hint: use randrange() from the random module to generate your number. Make sure that randrange returns the full range from 1 to 20 inclusive!

For this question, implement your solution in a main() function.

Blackjack

For the remainder of this assignment, you will be implementing functions for a game similar to Blackjack. Please read through the whole writeup before starting.

In this game, two players compete to get as close to 21 as possible, without going over. Both players start with a total of zero. Each turn, the players must decide whether to "Hit" or "Stand". If a player chooses to "Hit", the computer will pick a random value to add to their total. This random value should be chosen from the following sequence of numbers:

cards = [1,2,3,4,5,6,7,8,9,10,10,10,10,11]

[Hint: You can use random.choice(cards) to choose a value from cards]

If a player chooses to "Stand", nothing happens and their total stays the same. If a player goes over 21, they BUST and lose the game. If they get exactly 21, they win. If they both have values under 21, the player with the higher total wins.

In this assignment, you will implement a computer player, called the dealer, and (optionally) a human player, called the user. The user can choose to "Hit" or "Stand" however they like. However, the dealer must play according to strict rules.

• if the total is 17 or fewer, the dealer must "Hit"
• if the total is over 17, the dealer must "Stand"

The next questions will ask you to implement the following:

• a function that asks a human player whether they want to "Hit" or "Stand"
• a function that performs a dealer decision according to the rules above
• a program that simulates a dealer playing by itself
• (bonus) a program that allows a user to play against the dealer

The first two questions ask you to write a single function outside of the context where they would be used. To test them, we will call them from main() using test values. Testing functions with known inputs and outputs is called unit testing. If a unit test doesn't produce the correct output, we know there is a bug in our function!

2. To "Hit" or to "Stand"? This is the question

Complete the program, choice.py, that asks a user to choose whether to "Hit" or "Stand". If the user specifies something other than "Hit" or "Stand", the program should print an error and ask the user again.

Implement a function getChoice to ask the user for their decision.

getChoice

• Asks the user whether they would like to "Hit" or "Stand". Prints an error and re-asks if the user gives an unrecognized command.
• Parameters: None
• Return: either the string "Hit" or the string "Stand"

To test, we call getChoice() from main() and print the returned string.

 $ python3 choice.py
 What would you like to do? Hit or Stand? dance
 Sorry, unrecognized command: dance
 What would you like to do? Hit or Stand? Dance!
 Sorry, unrecognized command: Dance!
 What would you like to do? Hit or Stand? DANCE!
 Sorry, unrecognized command: DANCE!
 What would you like to do? Hit or Stand? ok, hit?
 Sorry, unrecognized command: ok, hit?
 What would you like to do? Hit or Stand? Stand
 The player selected:  Stand

3. Dealer Decision

Complete the program, decision.py, which simulates a dealer's turn. Recall that the dealer starts with a total of 0 and must play by strict rules:

• if the total is 17 or fewer, the dealer must "Hit"
• if the total is over 17, the dealer must "Stand"

If the dealer choses to "Hit", they get a random number from the following sequence of cards.

cards = [1,2,3,4,5,6,7,8,9,10,10,10,10,11]

[Hint: You can use random.choice(cards) to choose a value from cards]

If the dealer stands, nothing happens and the total stays the same.

Implement a function, doDealerTurn, which decides whether to hit or stand based on the dealer's current total.

doDealerTurn

• Performs a dealer turn. This function should print the dealer's current total as well as whether the dealer Hits or Stands. If the dealer Hits, also print the new value that will be added to their total.
• Parameter: dealerTotal, the current dealer total
• Parameter: cards, the sequence defined above
• Return: the amount to add to the dealer's total: 0 if the dealer stands; a value chosen from cards if the dealer hits

To test, we call doDealerTurn from main() with the values 1, 17, 19, and 21.

Using a random seed

Testing with random values is very difficult because we get slightly different output each time we run. However, if we set a random seed, the random module will generate the same numbers every time. The code below shows how we can set a random seed in main() before we run our unit tests.

   def main():
      random.seed(0) # Set the seed to 0

The following output was generated with random.seed(0)

$ python3 decision.py
--- First Test ---
The dealer has total 1
The dealer HITS and draws 11
Value returned by doDealerTurn: 11

--- Second Test ---
The dealer has total 17
The dealer HITS and draws 7
Value returned by doDealerTurn: 7

--- Third Test ---
The dealer has total 19
The dealer STANDS
Value returned by doDealerTurn: 0

--- Fourth Test ---
The dealer has total 21
The dealer STANDS
Value returned by doDealerTurn: 0

4. Blackjack Dealer - Solo Edition

Write a program dealer.py that simulates a dealer playing our Blackjack game. In the previous question, you implemented doDealerTurn. Copy your function to dealer.py. In this question, you will implement a new function, called checkGameOver which determines whether the dealer stands, wins, or goes BUST.

checkGameOver

• If the dealer's total is 21, prints that the dealer wins
• If the dealer goes over 21, prints that the dealer went BUST
• If the dealer goes over 17, prints that the dealer must stand
• Parameter: dealerTotal, the current dealer total
• Return: True if the game is over and False otherwise

Write a main() which implements a game loop. In main(), you should also keep track of the dealer's total score and the number of turns. The game loop should quit when checkGameOver() returns True. Each turn, you should update the dealer's score by calling doDealerTurn().

To test your program, set different seeds and make sure you can replicate the output below.

The following output was generated with random.seed(0).

 $ python3 dealer.py
 -------------
 Turn 1
 -------------
 The dealer has total 0
 The dealer HITS and draws 11
 
 -------------
 Turn 2
 -------------
 The dealer has total 11
 The dealer HITS and draws 7
 The dealer can only STAND (18).

The following output was generated with random.seed(1)

 $ python3 dealer.py
 -------------
 Turn 1
 -------------
 The dealer has total 0
 The dealer HITS and draws 3
 
 -------------
 Turn 2
 -------------
 The dealer has total 3
 The dealer HITS and draws 10
 
 -------------
 Turn 3
 -------------
 The dealer has total 13
 The dealer HITS and draws 11
 The dealer went BUST (24).

The following output was generated with random.seed(4)

 $ python3 dealer.py
 -------------
 Turn 1
 -------------
 The dealer has total 0
 The dealer HITS and draws 4
 
 -------------
 Turn 2
 -------------
 The dealer has total 4
 The dealer HITS and draws 5
 
 -------------
 Turn 3
 -------------
 The dealer has total 9
 The dealer HITS and draws 2
 
 -------------
 Turn 4
 -------------
 The dealer has total 11
 The dealer HITS and draws 10
 The dealer wins (21).

(Extra challenge) Blackjack: Dealer vs. Human

Write a program, blackjack.py, that allows a person to play against a dealer. Begin by copying dealer.py to blackjack.py.

This challenge builds on the features you implemented in the previous three questions. In this version, both a player and the dealer makes a decision to "Hit" or "Stand" each turn. Your program should ask the player what they want to do using the function getChoice(). Your program should use doDealerTurn to implement the dealer's turn.

Implement a function doUserTurn to perform the user's turn.

doUserTurn

• Performs a user turn. This function should print the user's current total as well as whether the user Hits or Stands. If the user Hits, also print the new value they got. This function should call getChoice to ask the user what they would like to do
• Parameter: userTotal, the current user total
• Parameter: cards, the values to choose from if the user selects "Hit"
• Return: the amount to add to the user's total: 0 if the user stands; a value chosen from cards if the user hits

Additionally, modify checkGameOver to handle new win conditions

checkGameOver

• Returns True if the game is over; False otherwise. Prints game results when the game is over.
• Parameter: userTotal, the current user total
• Parameter: dealerTotal, the current dealer total
• Returns: True if the game is over and False otherwise

The game can end in the following ways:

• If the user has 21, the user wins
• If the dealer has 21, the user loses
• If the user has over 21, the user loses
• If the dealer has over 21, the user wins
• If the dealer has over 17 and the user has more than the dealer without a BUST, the user wins

In main(), you should keep track of the user total, the dealer total, and the number of turns. As before, you should implement a game loop which exits when checkGameOver is True. Each turn, you should call doDealerTurn and doUserTurn to update the totals for each.

The following was generated with random.seed(0)

 $ python3 blackjack.py
 -------------
 Turn 1
 -------------
 The dealer has total 0
 The dealer HITS and draws 11
 You have total 0
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 7
 
 -------------
 Turn 2
 -------------
 The dealer has total 11
 The dealer HITS and draws 10
 The dealer wins (21).
 

The following was generated with random.seed(1)

 $ python3 blackjack.py
 -------------
 Turn 1
 -------------
 The dealer has total 0
 The dealer HITS and draws 3
 You have total 0
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 10
 
 -------------
 Turn 2
 -------------
 The dealer has total 3
 The dealer HITS and draws 11
 You have total 10
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 10
 
 -------------
 Turn 3
 -------------
 The dealer has total 14
 The dealer HITS and draws 10
 The dealer went BUST (24). You win (20)!

The following was generated with random.seed(2)

 $ python3 blackjack.py
 -------------
 Turn 1
 -------------
 The dealer has total 0
 The dealer HITS and draws 11
 You have total 0
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 11
 
 -------------
 Turn 2
 -------------
 The dealer has total 11
 The dealer HITS and draws 1
 You have total 11
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 2
 
 -------------
 Turn 3
 -------------
 The dealer has total 12
 The dealer HITS and draws 2
 You have total 13
 What would you like to do? Hit or Stand? Stand
 You STAND
 
 -------------
 Turn 4
 -------------
 The dealer has total 14
 The dealer HITS and draws 6
 You have total 13
 What would you like to do? Hit or Stand? Stand
 You STAND
 
 -------------
 Turn 5
 -------------
 The dealer has total 20
 The dealer STANDS
 You have total 13
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 11
 You went BUST (24)! The dealer wins (20).

The following was generated with random.seed(5)

 $ python3 blackjack.py
 -------------
 Turn 1
 -------------
 The dealer has total 0
 The dealer HITS and draws 10
 You have total 0
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 5
 
 -------------
 Turn 2
 -------------
 The dealer has total 10
 The dealer HITS and draws 10
 You have total 5
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 6
 
 -------------
 Turn 3
 -------------
 The dealer has total 20
 The dealer STANDS
 You have total 11
 What would you like to do? Hit or Stand? Hit
 You HIT and draw 10
 You win! (21)

5. Answer the Questionnaire

Each lab has a short questionnaire at the end. Please edit the QUESTIONS-04.txt file in your cs21/labs/04 directory and answer the questions in that file.

Turning in Your Labs

Don't forget to run handin21 to turn in your lab files! You may run handin21 as many times as you want. Each time it will turn in any new work. We recommend running handin21 after you complete each program or after you complete significant work on any one program.