Lab Exercise #1 Solution

Partner

We do our laboratory exercises with partners. In this way you can collaborate with someone else and, together, can figure out the problem. The experience you gain in the lab will help you with the project work. Remember, laboratory exercises are collaborative, project is homework to be done alone! Choose a partner in the lab to work with on this exercise. Two people should work at one computer. Occasionally switch who is typing.


Learning About the Terminal Application

At the beginning of most labs, will be a section on new skills to make you more proficent at the command line. Many tasks can only be performed at the terminal (or are easier to perform at the terminal), so becoming comfortable there is important. Many of the classes after this one will expect at least a basic familiarity of the command line, so pay special attention to these sections.

Log into Mimir and open the IDE. Use the terminal in Mimir's IDE to follow along.

pwd

The first command you need to learn is one of the simplest, pwd. At the terminal, type the command pwd and hit enter.

pwd is short for "print working directory". It outputs the path of the working directory, the directory your terminal currently has open. If you get lost (and it is easy to do with only the text-based terminal for navigation), pwd can show you where you are.

ls

The ls command outputs the names of all of the folders and files in the working directory. ls is short for "list" (as in "list" the contents).

Folder names end with a /, file names do not. Some terminals also add colorized output to ls to denote different types of files. For instance, Mimir's terminal has folders in blue, and files in white.

cd

The cd command is short for "change directory". It allows you to change your working directory to some different folder.

Lets say you run pwd and you get the output of:
/home/joshua/cse_232__summer_2017/lab01_new_horizons

Your current working directory is named "lab01_new_horizons". If you run ls, you would get:

lab01/

This means there is only one thing in this folder, a subfolder called "lab01". If you wanted to do things in that subfolder, you would use the cd command like so:

cd lab01

Now you are in the folder named "lab01", you can confirm such with pwd and ls

Special Directory Names

There are a few "special" directory names that you need to know. The first is the home directory. This directory's name is usually the username of the account, and it contains all of the user's files and folders. Inside the home folder is the "Desktop" folder (for all the things on your desktop), the "Downloads" folder and other folders as well (like "Music", "Videos", "Applications", etc.). The home folder is often specified using the tilde symbol (~). So if you want to cd to your home folder, run:

cd ~

Note: On most systems, running cd with no arguments also takes you to the home folder.

Sometimes you want to go the parent folder of your working directory. In the example above, we moved from the folder "lab01_new_horizons" to its subfolder "lab01". Trying to get back by running:

cd lab01_new_horizons

would fail, because there is no folder named "lab01_new_horizons" in "lab01".

The way to go to the parent directory (in this case "lab01_new_horizons"), you need to run:

cd ..

The .. directory (two dots)  is a strange way to symbolize the parent directory. In

fact, . directory (single dot) denotes the current working directory, the present directory that pwd would print, a fact that will be useful to know in later labs.

The last "special" directory is the root directory. The root directory is the directory that is the ultimate parent of all the other directories on the computer. It is denoted by the
single / symbol. In fact, you can specify any folder on the computer by starting with the root directory and working your way to the directory you actually want. Thus, the

path /home/joshua/cse_232__summer_2017/lab01_new_horizons is a fully qualified path. That is:

    • In the root folder (the starting /)

    • In the folder named "home" (a subdir of the root)

    • In the folder named "joshua" (a subdir of home)

    • In the folder named "cse_232__summer_2017" (a subdir of joshua)
    • In the folder named "lab01_new_horizons" (a subdir of cse_232__summer_2017)

It is an unambiguous statement of location.

Assignment Overview

This assignment involves coding and testing of a program based on the “Hello World” program from the lab 00, and then using the Mimr program to hand it in. Mimir provides a series of tests that get run every time you handin. It gives you feedback on how well your program works. When you pass all the tests, you are done! If you can't pass all the tests, turn in what you can and pass as many tests as possible. Always turn something in!

You can turn in programs using Mimir as often as you want. Try turning in the “Hello World” program (or the completed project) during lab so if there is a problem, the TA can help you solve it. During lab you start the project so that if you need help, you are still in lab with the TA available. Complete the project and hand it in again when done. Remember, the last thing you handin before the deadline is what gets graded, everything else is ignored!

The basic design of the first programs that you construct in this class consists of a prompt for information, receiving information, processing that information then producing a display of the results.

Background
The New Horizons spacecraft, launched January 19th 2006, is the first earth spacecraft to have
made contact with the planet Pluto. On January 1st, 2019 it is schedule to make contact with the
first Kuiper belt object KBO-2014-KU69. The NASA update page

(http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons/index.php) reports it (09/01/2017) at a
distance of 39.33Astronomical Units (AU) from the Sun, traveling away from the Sun at 14.24
km/sec, 8.85 mi/sec.

For this lab you will use the cin and cout streams along with some simple mathematics for calculating New Horizon's distance. The important part of the project is to learn the skills needed to access the class web site, to access a project description, create a new program in C++ and finally to hand it in.

Your Task
Your program will prompt the user for an integer number (a number without decimal points) which indicates the number of days after 09/01/2017, starting at the distance 39.33 AU from the sun. You will calculate the distance of New Horizons from the Sun using the numbers from 09/01/2017 (assume velocity is constant) plus the user provided number of days and report:

        ◦ Updated distance in A.U.

        ◦ Distance in kilometers (1 AU = 149,598,000 km) on a line by itself

        ◦ Distance in miles (1 AU = 92,955,800 mile) on a line by itself

        ◦ Round trip time for radio communication in hours. Radio waves travel at the speed of light, listed at 299,792,458 meters/second, on a line by itself

        ◦ provide 2 decimal points of accuracy using std::fixed and std::setprecision (the later requiring #include<iomanip>). You would use them as follows:
            ▪ std::cout << std::fixed;

            ▪ std::cout << std::setprecision(2);

    • indicates that you need to show your TA your progress at this point. Please show your TA:

        ◦ Your working program

Assignment Notes:

There is a Mimir assignment labeled Lab01: New Horizons with 3 test cases. There is a starter file with the correct directory and name, lab01.cpp, but no content (nothing in the file).

There are some rounding issues here so be careful! To make the km calculations, us the constants (speed and distance) provided. To make the mile calculations, use the constants (speed and distance) provided. To make the round trip calculation, use your distance in km and the speed of light constant provided. You'll get slightly different answers if you try to convert the two distance or the two speeds.

Use the provided inXX.txt and outXX.txt examples, where XX is the test number: in1.txt should match out1.txt, int2.txt should match out2.txt and so on. The output should match exactly.

You will need to work with the cin and cout streams and their operators >> (for cin) and << (for cout). You will also need to declare the appropriate variables: long (a 64 bit integer) for values like days and double for calculation values.

cout takes either variable values or strings (between " ") and outputs them to the console. You can use multiple << operators on the same cout stream, usually ending with endl . Assuming the variable int_var has the value 23:

std::cout << "This is a string: "<< int_var << " the end" << std::endl;
would ouput:

This is a string: 23 the end
cin will input a value from the command line into a variable of a particular type. It does so until it hits a space (space separated values) or an end of line. For example:

std::cin >> int_var;

If you enter a value on the command line, an integer, it will be read into the variable (no conversion required).

int multiplier, number;

std::cin >> number;
std::cin >>    multiplier;

std::cout << "The number "<<number<< " times "<< multiplier <<" is "<< number * multiplier << std::endl;

With inputs 10 and 2 respectively, you would get

The number 10 times 2 is 20

Look at the examples in the Week 1 examples for a little guidance.

The operations on these numbers are, respectively: + (sum), - (difference), * (product), / (division) and % (remainder, integer only). The last two deserve special comment.

If an integer is divided by another integer, the result is an integer. Thus the result of 6/4 is 1. In contrast, 6.0/4 is 1.5. That is, the / operation results in the integer quotient if using integers, floats if using floats. The result of 6%4 is the integer remainder of the division, thus 2 (6 divided by 4 is 1 with a remainder of 2). There is no equivalent for % in floating point math.

Getting Started

    1. Create a new directory in the way discussed in the videos and call it lab01
    2. Save the the program, making sure the name is lab01.cpp
    3. Using the example from the 4 hello world programs, write the code.
        a. Don't worry if you get an error that looks long and difficult. C++ is like that. Look at the first error and find its associate line number. That is the best clue.

    4. Run the program
    5. Edit the program to fix any errors or add functionality
    6. Now you enter a cycle of edit-save-compile-run to incrementally develop your program.

Questions for you to consider

    1. What happens when you try to divide by zero when you run your program?
    2. What happens when std::cin a letter instead of a number?