Ttt 9 Play Loop

Objectives

  1. Use a loop within a method.
  2. Use a looping method within a CLI.
  3. Call a method within a loop.

Overview

In this lab you're going to build a #play method for Tic Tac Toe that initiates a simple loop and calls #turn. It won't function like a real game of Tic Tac Toe but instead as a very simplified version. Our #play method will initiate a loop that runs 9 times, simulating an entire game.

Instructions

Part I: Understanding the Helper Methods in lib/play.rb

You'll notice that we've added some helper methods for you in here that you already created in previous labs. Take a look at our code and notice how it's probably different than how you wrote those methods. Isn't it cool that there are so many ways to write the same method? Now try to understand how these methods work together in the #turn method to represent a turn of Tic Tac Toe with move validation.

There are no tests for these methods, and if they stop working as they do currently your lab will break because your #play method will depend upon a functioning #turn method. Edit these methods at your own risk.

Part II: The CLI

Before you begin building the #play method in lib/play.rb, you should first take a look at the CLI provided in bin/play. This code will require your lib/play.rb library, initialize a starting board, and welcome the user. You can run it with ./bin/play or ruby bin/play from your terminal. You'll see:

Welcome to Tic Tac Toe!
   |   |
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   |   |   
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   |   |   

The CLI shows the start of the game but doesn't start playing the actual game. Your #play method will provide that logic. It'll be easier to code #play if you can actually use the CLI to see how your method changes the behavior of the game. Edit bin/play to include a call to #play, passing it the board as an argument. You can add that line to the bin/play CLI in advance of actually defining the #play method in lib/play.rb. If you try running your CLI now, you'll get a NoMethodError about an undefined method #play, which is fine because that's what we're about to define.

You can make sure your CLI is working by running learn spec/01_cli_spec.rb or rspec spec/01_cli_spec.rb.

Part III: The #play Method

You must build a #play method in lib/play.rb. (You can add it anywhere but at the bottom would be nice.)

The #play method should:

  • Accept an argument of a board.
  • Start a loop and call #turn.

A few things to think about:

  • What constitutes a rousing game of Tic Tac Toe? Do the two players simply keep filling out squares forever and ever? Definitely not. Eventually the game must end. In fact, there are only 9 spots on a Tic Tac Toe board, so there is a maximum of 9 turns to be played. Account for this in the loop(s) that your #play method contains.
  • Which looping construct (while, until, etc) you use doesn't really matter. What does matter is how and when you terminate the loop. You don't want to get stuck in an infinite loop when you execute your bin/play file or when you run the tests through learn or rspec. You'll notice you're in an infinite loop if you run the test or bin file and it "hangs," never terminating. If you do get stuck, just type CTRL+C to terminate the process.

As you code and try to get the tests to pass, play with your CLI and make sure that it is looping, allowing you to play multiple turns of Tic Tac Toe even if they are unrealistic according to the rules of the game. (We'll move on to working out who wins the game in a later exercise.)

A working #play method will produce a CLI that behaves as follows:

$ ./bin/play
Welcome to Tic Tac Toe!
   |   |   
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   |   |   
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   |   |   
Please enter 1-9:
1
 X |   |   
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   |   |   
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   |   |   
Please enter 1-9:
1
Please enter 1-9:
2
 X | X |   
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   |   |   
-----------
   |   |    
Please enter 1-9:
3
 X | X | X
-----------
   |   |   
-----------
   |   |   

Remember that when you see a number in this sample output it represents user input. In this game, the first move was to position "1", the second move attempted to also move to position "1" but was denied because of validation. After the validation failure, the user entered "2", the board marked an "X" instead of an "O" in position "2", and the move was completed. The user then entered a "3" and the board was further updated. Subsequent turns would continue in a similar fashion until the enclosing loop(s) terminated.

Note: Don't just call the #turn method 9 times inside the #play method. Use the looping constructs we've learned in previous lessons!

Conclusion

Once you get all the tests passing, your #play loop should be looking pretty good. However, there are two issues with it. First, the turns do not switch between "X" and "O" tokens. Second, the game does not terminate when a player wins. Take a moment and brainstorm––what are some ways in which we could tell our game to switch tokens according to whose turn it is? How could we determine if and when a certain player has won?

We'll be building all of these functionalities soon; for now, it's just food for thought.

View Tic Tac Toe Play Loop on Learn.co and start learning to code for free.

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