lab01 : Crunching numbers: Loops and Functions

num ready? description assigned due
lab01 true Crunching numbers: Loops and Functions Tue 07/03 09:00AM Sun 07/08 11:59PM

Goals for this lab

In this lab you will get practice

Log on and create a local directory

You are now ready to get the starter code.

Getting the starter code

Copy the code from the instructor’s account on the CSIL server into your local lab01 directory by issuing the following command:

$cp /cs/faculty/richert/public_html/cs16/lab01/* ~/cs16/lab01/

After doing this command, if you cd into ~/cs16/lab01/ and use the ls command, you should see three .cpp files and a README:

-bash-4.2$ ls
min2.cpp  min3v1.cpp  min3v2.cpp README.md
-bash-4.2$

If you don’t see those files, go back through the instructions and make sure you didn’t miss a step. If you still have trouble, ask a TA for assistance.

Create a repo on github in our class organization

For this lab and all subsequent programming assignments, you should start by creating a repo in the ucsb-cs16-m18 organization you joined as instructed in lab00. Follow these steps

new-repo

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.

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.

Upload your files to your repo on github using github’s web interface following the instructions at the beginning of this lab.

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), 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)

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.

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: CS16 Summer 2018. 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 your local machine or submitting the code that is in a github repo. Select the second option and select your github repo for this assignment. You should receive 100/100 for a completely correct program.

Done!

If you are in the Phelps lab or in CSIL, make sure to log out of the machine before you leave. Also, make sure to close all open programs before you log out. Some programs will not work next time if they are not closed. Remember to save all your open files before you close your text editor.

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

$ exit

Grading rubric

In addition to the points given by gradescope, our staff will be manually grading your code for style. 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

Github Resources