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COMP251

Programming Kata 0

Welcome to your first programming exercise for your portfolio!

If you have not already done so, follow the instructions in the portfolio intro. You must do this before starting this assignment!

If you have not done so yet already, clone your portfolio on lily.

$ git clone <your-portfolio-url>

Change your working directory to inside the portfolio and create a new branch for this assignment.

$ cd <your-portfolio-directory>
$ git checkout -b exercise00

Validate that you are indeed using a branch (the output should start with “On branch exercise00”):

$ git status

You must work within branches! Do not commit code to the main branch – if you do this, you will be penalized points. We are trying to model best practices in this class and develop some process skills that you will use in all future classes.

Now, create a subdirectory for this exercise and change your working directory to inside it.

$ mkdir exercise00
$ cd exercise00

Now create your C file and start coding!

$ vim collatz.c

Assignment

Write a program that computes the total number of iterations for (user-inputted) numbers to complete their Collatz sequences.

The Collatz sequence for a number is the sequence of numbers that are output when following the following algorithm for a given input n (n must be greater than 1):

“as long as n is not 1: if n is even, n becomes n/2; otherwise, n becomes 3n+1.”

For example, consider a starting value of 10: 10 is even, so the next number is 5. 5 is odd, so the next number is 16 (3*5+1). 16 is even, so the next number is 8 (then 4, then 2, then 1).

The total length of this sequence (10, 5, 16, 8, 4, 2, 1) is 7.

You can have a termination condition that validates that the number is greater than 0, or you can just use CTRL-C to quit.

$ gcc collatz.c -o collatz
$ ./collatz
Enter a number: 12
12 -> 10
Enter a number: 19
19 -> 21
Enter a number: 2
2 -> 2
Enter a number: 6
6 -> 9
Enter a number: 7
7 -> 17
Enter a number: 26
26 -> 11
Enter a number: 27
27 -> 112
Enter a number: ^C
$

Tips

  • You should write a function to compute the number of iterations for a given number.
  • Use scanf and printf to perform input and output.
  • You should add input validation; quitting when the number is not greater than or equal to 1 is a fine behavior.

Turning it in

When you are complete, commit your code and create a pull request with your exercise.

Change to the root directory of your repository:

$ cd ..

Add a line to the .gitignore file to exclude your binary.

$ echo exercise00/collatz >> .gitignore

Add the new directory (and file) to your staged commit and verify your files are staged.

$ git add exercise00   
$ git add exercise00/collatz.c
$ git status

Commit your code and push it to GitHub!

$ git commit -m "<your commit message>"
$ git push -u origin exercise00

There will be a link to create a pull request in the upload message. Click the link and create a PR. Assign me as reviewer.