lab03 : Crunching numbers: Loops and Functions

num ready? description assigned due
lab03 true Crunching numbers: Loops and Functions Mon 10/18 12:00PM Mon 10/25 11:59PM

Goals for this lab

In this lab you will get practice with:

Step 0: Log on to COE/CSIL/ECI account, cd into cs16

Log into your CoE account on CSIL, open a terminal, and use cd to move into the cs16 directory you created in a previous lab.

Step 1: Find your lab03 repo on GitHub

You should have an empty repo on GitHub under the name lab03-YOUR-GITHUB-ID.

Following the steps outlined in a previous lab, please use the SSH address to clone this repo, i.e.

git clone git@github.com:ucsb-cs16-f21/lab03-YOUR-GITHUB-ID.git

After that, you should have a directory under cs16 called lab03-YOUR-GITHUB-ID. Use the cd command to move into this directory:

cd lab03-YOUR-GITHUB-ID

You may want to practice moving between this directory and the parent directory a few times, and using the ls and pwd commands to understand what is happening:

cd ..
pwd
ls
cd lab03-YOUR-GITHUB-ID
pwd
ls

Then, as a reminder, while in your ~/cs16/lab03-YOUR-GITHUB-ID directory (remember that ~ stands for your home directory), use ls -a to see that while the directory may appear empty, there is a hidden folder called .git that marks this folder as a git repository (or repo for short):

$ ls -a
.  ..  .git
$

Step 2: Create the main branch in your repo

Every git repo can have multiple branches of code; this is useful on projects where there are multiple programmers collaborating on a solution. Multiple branches allow for different versions of the code to live side-by-side in a repository, and then be merged together at a later stage.

This single branch is sometimes called the default branch.

Not all git software is updated with this convention however. Accordingly, when we clone a new repo, to align our local repo with GitHub, our first step is to set the current branch to main, with this command (please type this now in your ~/cs16/lab03-YOUR-GITHUB-ID directory:)

git checkout -b main

The git checkout command is the one that is used to switch from one branch to another, and the -b command says that we are creating a new branch in our local repo.

For the time being, and probably throughout CS16, this is likely everything you need to know about branches (at least for the purposes of this course.)

Now we are ready to pull in some starter code.

Step 3: Add a remote for starter code.

While in your ~/cs16/lab03-YOUR-GITHUB-ID directory, type this command:

git remote -v

The -v here stands for verbose, and it means that the command will give lots of helpful information. The output should look like this:

$ git remote -v
origin	git@github.com:ucsb-cs16-f21/lab03-YOUR-GITHUB-ID.git (fetch)
origin	git@github.com:ucsb-cs16-f21/lab03-YOUR-GITHUB-ID.git (push)
$

Explanation:

What we are doing to do next is add a second remote, called starter. From this remote, you’ll be able to pull in some starter code; your lab solution will involve working with some of that starter code.

The starter code lives in this repo, which you can visit in a web browser to look at the starter code:

To add a remote for this repo, we’ll use the ssh url, like this:

git remote add starter git@github.com:ucsb-cs16-f21/STARTER-lab03.git

To see if it worked, you can type the git remote -v command again. Output should look like this (with YOUR-GITHUB-ID replaced by your github id.

$ git remote -v
origin	git@github.com:ucsb-cs16-f21/lab03-YOUR-GITHUB-ID.git (fetch)
origin	git@github.com:ucsb-cs16-f21/lab03-YOUR-GITHUB-ID.git (push)
starter	git@github.com:ucsb-cs16-f21/STARTER-lab03.git (fetch)
starter	git@github.com:ucsb-cs16-f21/STARTER-lab03.git (push)
$

Note that if the URLs are wrong for either the origin or the starter remotes, you can fix that by doing this command to remove a remote:

Then you can add the remote back with the correct URL, e.g.:

This can be used, for example, if you accidently cloned the repo using the https url instead of the one that starts with git@github.com (which is the SSH based URL).

Assuming your remote for starter is now set up correctly, the next step is to pull in the starter code.

Step 4: Pull in Starter Code

To pull in the starter code, use:

git pull starter main

Then use an ls command, and you should see new files in your directory. That should look something like this:

$ ls
$ git pull starter main
remote: Enumerating objects: 10, done.
remote: Counting objects: 100% (10/10), done.
remote: Compressing objects: 100% (7/7), done.
remote: Total 10 (delta 2), reused 7 (delta 2), pack-reused 0
Unpacking objects: 100% (10/10), 2.45 KiB | 47.00 KiB/s, done.
From github.com:ucsb-cs16-f21/STARTER-lab03
 * branch            main       -> FETCH_HEAD
 * [new branch]      main       -> starter/main
$ ls
LICENSE  min2.cpp  min3v1.cpp  min3v2.cpp  README.md
$

With these files in place, you are ready to start coding.

If you don’t see those files, go back through the instructions and make sure you didn’t miss a step.

Step 5: Solving the problems for this lab

This assignment consists of 3 problems, each of which is described below. The first one is worth 20 points each, and the last two are worth 40 points each. Each should be solved in its own file and all three must be submitted for full assignment credit. These exercises are inspired by the ones from the textbook (in Ch. 2 and Ch. 3) - but they are NOT the same, so follow the instructions for this lab carefully.

You will need to create three files named block.cpp, min4.cpp, and pi.cpp: Each corresponds to one of the problems listed below, which make up this lab.

For a reminder on how to open and use a text editor to create and edit new source files, refer back to lab00.

For all the subproblems given in this assignment you must compile your code frequently (as you develop it), and test it extensively with as many inputs as you can think of.

Step 5a: Print a block

A session should look exactly like the following example (including whitespace and formatting - note that there is no whitespace at the end of each of these lines), for all the different inputs and the output:

$ ./block
Enter number of rows and columns:
1 5
X.X.X.X.X.
Enter number of rows and columns:
2 2
X.X.
X.X.
Enter number of rows and columns:
2 5
X.X.X.X.X.
X.X.X.X.X.
Enter number of rows and columns:
10 5
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
X.X.X.X.X.
Enter number of rows and columns:
0 1

Each string printed by the program should include a newline at the end, but no other trailing whitespace (i.e. extra space characters at the end of the line).

For this problem you have to use a for-loop, and a while or do-while loop. While loops are similar in that the code inside the body of the while is repeated as long as the while condition is true. We will talk about this more in lecture this week. Here is the syntax for a while loop:

while ('expression') {
	//Repeat these statements
}

‘expression’ should be replaced by the appropriate boolean expression. The body of the loop is executed as long as the expression is true. e.g.

int x = 5;
while (x > 0) {
	cout << x << " ";
	x--;
}

The above code prints 5 4 3 2 1.

To compile your code use the g++ command as in lab01 OR the simple make command.

$ g++ -std=c++11 -o block block.cpp

OR

make block

If you used the first option (g++ ...) note that the -std=c++11 option in these commands is optional to use (that is, not critical to define). All this does is force the compiler to use the C++11 version of C++.

If you used the second option (make...) note that the make program is clever to compile only block.cpp into the block executable, even though there are other programs (cpp files) in that directory. Note that the C++11 compiler will not be used in the default make tool. But that should be okay for now.

If you encounter an error, use the compiler hints and examine the line in question. If the compiler messsage is not sufficient to identify the error, you can search online to see when the error occurs in general.

Run your executable as follows to test it out. $ ./block

Remember to re-compile the relevant files after you make any changes to the C++ code.

Once your program works properly, you can use the commands in Step 6 to add the block.cpp C++ source code file to your repo. Skip down to Step 6 for that explanation, then return to Step 5b to continue with the next programming exercise.

Step 5b: Calculate the approximate value of PI

Write a C++ program in a file named pi.cpp that approximates the value of the constant π. Once again you should not resort to using predefind constants and functions for π, that are provided by C++ standard libraries. Instead you should compute the value of π based on the Leibniz formula for π. The formula is given below:

 1 – 1/3 + 1/5 – 1/7 + 1/9 ...  = pi/4

Put another way, the formula can be written as:

pi = 4 · [ 1 – 1/3 + 1/5 – 1/7 + 1/9 ... + (–1 ^ n)/(2n + 1) ]

The Leibniz formula works well for high values of n.

The program takes an input from the user for the value of n, which determines the number of terms in the approximation of the value of pi. The program then outputs the approximated value of pi as calculated by the Leibniz formula. You must also include a loop that allows the user to repeat this calculation for new values of ‘n’ until the user says she or he wants to end the program by issuing an input of -1 (or any other negative number). You may assume that the user always inputs an integer.

The program should print a string of text to the terminal before getting each piece of input from the user. A session should look like the following example (including whitespace and formatting - note “term” in the output below is not plural when using 1, but is plural in other cases for example), showing the expected output for different inputs:

Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
0
The approximate value of pi using 1 term is: 4.000
Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
3
The approximate value of pi using 4 terms is: 2.895
Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
9
The approximate value of pi using 10 terms is: 3.042
Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
49
The approximate value of pi using 50 terms is: 3.122
Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
99
The approximate value of pi using 100 terms is: 3.132
Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
999
The approximate value of pi using 1000 terms is: 3.141
Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
9999
The approximate value of pi using 10000 terms is: 3.141
Enter the value of the parameter 'n' in the Leibniz formula (or -1 to quit):
-1

Be sure to have a newline after each “Enter the value…” prompt and no other white spaces.

Here is a link that gives the approximated values of pi for up to 1000 terms: http://www.eveandersson.com/pi/gregory-leibniz

In addition, all approximated floating pointer numbers must be displayed to exactly three digits after the decimal point. To do this you should use set the precision for displaying floating point numbers before any of the cout statements in your code. This is done as follows:

cout.setf(ios::fixed); 	   // Display in fixed point notation. For example, display 1e-1 as 0.1
cout.setf(ios::showpoint); // Always display the decimal point.
cout.precision(3);         // Set the number of digits to display after the decimal point to 3

To calculate x to the power of y, use the pow(x,y) function from the standard library. To do this you will need to include the header file: cmath

Upload your files to your repo on github using github’s web interface. (You will need to be on a csil machine and not remotely logged in to do this step)

Step 5c: Calculate the minimum of 4 numbers

In this part of the lab you will write a program that compares 4 input numbers and prints out the smallest one.

You should not use the min() function in C++ algorithm library or any other outside function that performs the minimum operation for you. Instead, you should base the program on the example programs provided to you that compare fewer inputs.

Start by examining the given examples, also described below:

min2.cpp

This program takes two command line arguments, and converts them to integers. It then calls a function, smallest_of_two, that returns the smallest of the two numbers (or the value they share in case of a tie.) It then prints out the result of that function call.

min3v1.cpp

This is the first of two versions of a program that takes min2.cpp one step further, finding the smallest value from among three numbers. Again, if there is a tie, it prints the tie value. Look at the nested if/else statements and see if you can make sense of the logic. Seek help if you don’t.

min3v2.cpp

This program does EXACTLY the same thing as min3v1.cpp, but does it with much cleaner, simpler code. Notice how we REUSE the smallest_of_two function to build up a smallest_of_three function.

Your job in this step is to test min2, min3v1 and min3v2 with many different values and convince yourself that they work properly.

In the next step, you will be taking these programs to the next logical step in this sequence.

Your main task: Write min4.cpp

If you DO use nested if/else statements, though, be sure that you indent and format your code appropriately.

Follow the pattern in min2 and min3v1/min3v2 in terms of all other issues and how they are handled, including the usage message, etc. Your program should look exactly like these except that it works on 4 inputs (note, there are no trailing whitespacse):

./min4
Usage: ./min4 num1 num2 num3 num4
 Prints smallest of the four numbers

Here is the output of the program with the correct number of inputs:

$ ./min4 3 4 5 6
3

Here are two more example runs:

$ ./min4 92 35 12 17
12

$ ./min4 92 -35 12 17
-35

To compile your code use the g++ command as before.

$ g++ -std=c++11 -o min4 min4.cpp

Run your executable with different inputs to test it out.

Upload your files to your repo on github using github’s web interface.

Step 6: Commit your code to GitHub

When each of your programs is done, you can commit your code to GitHub.

You can wait until all three are finished, but you are encouraged, instead, to do this one by one as each program is complete.

For example, to commit the program block.cpp to GitHub, use these steps:

Step Command to type What is happening
1. git add block.cpp. This adds the file block.cpp to something known as the staging area. This prepares the file to be added to our git repo.
2. git status This command shows us the current status of our repo. We should see that the file block.cpp appears in green, as a file “to be committed”.
3. git commit -m "add block.cpp to repo" This commits the files in the staging area to the local repo on CSIL. The -m stands for message, and the part in the quotes is the message. Every commit has a message to our future selves and to other programmers about what we were doing when we made this commit. Learning how to write good commit messages is an important skill.
4. git push origin main This pushes the changes from our local repo on CSIL to the original repo that we cloned (i.e. origin on github.com

You can repeat the steps above for the files pi.cpp and min4.cpp as/when you have them ready.

Note that if you subsequently make changes to any of the files block.cpp, pi.cpp or min4.cpp, the process to update GitHub is the same—that is, you still use git add filename.cpp when you want git to pick up changes to files that are already in the repo.

At any time, you can type the git status command and it will help you determine which files, if any, are out of date in your repo. For each out of date file, the sequence git add filename.cpp, then git commit -m "message goes here" then git push origin main should get the changes published to your GitHub repo.

You can visit your repo at any time by logging in to GitHub, and visiting https://github.com/ucsb-cs16-f21, where you should see it in the list of repos to which you have access. If you don’t see it there, ask the staff for assistance.

Step 7: Submit your code on gradescope

Once you are satisfied that your program is correct, then it’s time to submit it.

Log into your account on https://www.gradescope.com/ and navigate to our course site: CMPSC 16. Select this assignment.

Then click on the “Submit” button on the bottom right corner to make a submission. You will be given the option of uploading files from GitHub.

You should receive 100/100 for a set of completely correct programs, and partial credit if one or two of the three is correct.

If any errors are shown, you can address that with this sequence of steps:

Step 8: Done!

If you are logged in remotely, you can log out using the exit command:

$ exit

Grading rubric

Though it does not apply to this lab, in future weeks, in addition to the points given by gradescope, our staff will be manually grading your code for style. So you may want to look over your code for the following items.

Code style, includes but is not limited to the following:

  1. Code can be easily understood by humans familiar with C++ (including both the author(s) of the code, and non-authors of the code.)
  2. Code is neatly indented and formatted, following standard code indentation practices for C++ as illustrated in either the textbook, or example code given in lectures and labs.
  3. Variable names choices are reasonable.
  4. Code is reasonably “DRY” (as in “don’t repeat yourself”)—where appropriate, common code is factored out into functions.
  5. Code is not unnecessarily or unreasonably complex when a simpler solution is available.

If you’d like feedback on your coding style, you may ask one of the staff during discusssion section or office hours.