Computer Science 1 CSci 1100 Lab 1: Variables, Assignments, Expressions and Submitty

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Computer Science 1 | CSci 1100
Lab 1 | Variables, Assignments, Expressions and Submitty
Fall Semester 2016
Lab Overview
This lab has two goals: (1) to learn how to use Submitty the submission server we will use
for submitting homeworks and checking grades, and (2) to practice writing short programs
that involve variables, assignments and expresssions. This will be accomplished by three
small checkpoints. Throughout, we will also practice nding and xing syntax and semantic
errors, begin our study of good program structure and also learn what hard-coding is and
how to avoid it.
Checkpoint 1: Introduction to Submitty
For each set of lecture exercises and for each homework assignment you will log into Sub-
mitty, upload your code programs, run them, and view the results. For checkpoint one
we will concentrate on submitting a single python le in order to get a correctly running
program with no syntactic or semantic errors.
Go to the resources page from our Piazza site and download the program lab1 volume.py.
(Store this in a folder you create within your Dropbox folder structure for Lab 1.) Bring up
the Wing IDE and Open this le (click File and then Open and navigate to the desired le)
so you can look at the program closely. Rather than making you write your own program for
this rst part, we will start with this \ awed” version just to demonstrate some important
aspects of Submitty. Note that this le is intended to calculate the volume of a cone. If you
are fuzzy about the correct formula, it is 1=3  area of base  height. I am going to assume
you can calculate the area of the circular base!
This simple Python program contains both syntax and semantic errors. Don’t x these
errors yet, even if you know what they are! If you don’t remember the di erence between
a syntax error and a semantic error, look back at the Lecture 2 notes.
First, we want to familiarize you with the various errors messages you will get when you
run your own program in the Wing IDE and when you upload a program to Submitty that
has errors. Please follow these steps:
(a) Look at lab1 volume.py in the IDE and, without making any changes, attempt to run
it (click the green triangle/arrow). It will complain of syntax error(s). Do NOT x
these errors yet. Instead, upload this le as is to Submitty to see what happens.
(b) To do this, cut-and-paste the following link to the submission page into a browser (or
click below)
https://submitty.cs.rpi.edu/index.php?semester=f16&course=csci1100
and login with your RCS id and password. Note, if your RCS id is abcde@rpi.edu, your
login for Submitty will be abcde and your password will be your RCS password for that
account. The submission server is also linked from the Piazza site under Resources if
you need to nd it later.
(c) Once you are logged in, click on the Submitty Practice item. This will bring up a
submission window. Either drag your lab1 volume.py le into the submission box, or
click in the box and select your le from the le browser. Click Submit to start the
grading process.
This is what the server shows you when your program has syntax errors. (Python only
shows one syntax error at a time, so if you have multiple syntax errors in your program
you will only see the rst one.)
(d) Now it is time to nd and x the syntax error(s). It would be best if you do not x
any semantic error(s) you may nd yet. We recommend that you edit the le in your
Wing IDE and use Wing to get the program to run rather than using Submitty as a
syntax checker. Keep correcting syntax errors and then checking the program by using
the green arrow in Wing until you have made sure that the program runs on Wing IDE.
(e) At this point, we want to demonstrate how Submitty shows semantic errors. Submit
the syntactically-correct version of lab1 volume.py to the homework server by again
loading your program into the submission block. Answer Y if asked if you want to
replace the le. Once the le is loaded, hit Submit, and review the di erence between
your results and the expected results for any discrepancies. Here is an example
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Places where your solution di ers from the expected solution are shown in red
(f) Finally, x the semantic errors in the program and resubmit. Repeat this as many
times as you need to until your answer exactly matches ours.
To complete Checkpoint 1: show a TA or a mentor that you have successfully
submitted both correct and incorrect versions of the program to Submitty.
Final note on the homework server: You have seen at this point that multiple
submissions of the same assignment are accepted on the homework server. There is no limit
to the number of times you may submit. The server keeps track of all submissions. Please
be aware, however, that the TAs will only look at the active version when grading your
homework, which is usually the latest version unless you designate an older version as the
active version.
Also be aware that the server may run your program slower near deadlines, making you
wait to see the results of your program. Make a habit of testing your program before you
submit to avoid unnecessary delays. Note that in terms of deadlines what matters is when
you submitted the program, not when it showed you the output.
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Checkpoint 2: Submitting Lecture Exercises
The Lecture 2 exercises asked you to write two short Python programs and to generate a
le containing the output from a program. In this Checkpoint you will upload these three
les to Submitty.
Start by navigating back to the CS1100 start page using the links at the top of the page.
This time, select Lecture 02 Exercises. Since Lecture 02 asked you to submit 2 python
programs and 1 text le, you will notice that there are 3 submission blocks on the page
labeled for the 3 problems you were asked to solve. These three boxes work independently.
You can upload solutions to any or all of the parts independently before running submit.
For example, the following screen shows a submission with only the rst question answered.
You can iteratively add the rest of the answers in, and you can change any or all of
the solutions independently at any time. When you hit Submit the most recent versions
of each le will be evaluated and scored. All lecture exercises will be automatically scored
without TA intervention. To make sure that you are following instructions, we have the
ability to inspect the code. Clicking on the Details link shows what we are looking for in
the answer as shown below.
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For Lecture 2 we are counting print statements, multiplication operators and assignment
statements to be sure you are using the correct number based on the instructions. We are
being very speci c in our messages for this set of exercises; that may not always be the case.
If you are having issues getting your tests to pass, re-read the instructions and make
sure you are following all of the guidelines.
Additional details on using Submitty can be found at https://github.com/Submitty/
Submitty/wiki/STUDENT-SUBMITTER. Expect them to be updated as the semester pro-
ceeds.
To complete Checkpoint 2: show a TA or a mentor that you have successfully
submitted correct Lecture 2 Exercises to Submitty.
Checkpoint 3: How big is your hard disk?
How much data can your hard drive store? This question is harder to answer than you think.
The main measure of data in computers is a byte. For example, an integer in Python is 8
bytes.
In computer science, a gigabyte (GB) is a measure equivalent to 210210210 = 230 bytes.
In fact, most operating systems use this convention. A terabyte (TB) is 1024 gigabytes, or
240 bytes. We call this base 2 computation; everything is a power of 2.
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However, computer manufacturers nd this too complicated. So, instead they use base
10 computation. When they sell you a computer, a gigabyte is assumed to be 103103103 =
109 bytes. A terabyte similarly is 103 gigabytes, i.e. 103  109 = 1012 bytes.
So, when you buy a 128 GB hard disk (manufacturer de nition, base 10) and put it in
your computer, your computer will record that it is actually 119 GB (computer de nition,
base 2). As a result, you have somehow lost 9 GB before even using your computer. Sad
but true.
In this checkpoint, you will write a program that prints out this size di erence. To
accomplish this, you are going to write a new Python program.
(a) Start by clicking File -> New in the IDE to create a new program to type into.
(b) In this new program, create a variable called base10size and assign 128 to this variable
to represent the number of base 10 \gigabytes”.
(c) Create a new variable called base2size and assign it the size of 128 base 10 \gigabytes”
converted to base 2 \gigabytes”. Do this by multiplying base10size by 109 (a base 10
gigabyte) and then dividing by 230 (a base 2 gigabyte).
(d) Create a variable called lost_size that stores the di erence between the two gigabyte
sizes.
(e) Finally, write a print statement to output the result in the following format using your
variables:
128 GB in base 10 is actually 119 GB in base 2, 9 GB less than advertised.
Now, save this (very short) program to a le called lab1 part3.py in your Lab 1 dropbox
folder. Run it to make sure it is correct. Once it is complete, reuse your code to print the
same information for hard disk sizes of 256 GB, 512 GB and 1024 GB as well. If you did
this right, all you have to do is copy all your code, and change only the value of the base
10 variable. It looks repetitive right? We will talk about that in class in a few weeks!
No hard-coding: You must use three variables for this solution, with no hard coding of
values other than the initial assignment to the variable base10size. What is hard-coding?
It is writing the solution directly into a program. In these early exercises and homeworks,
the problems are easy so we may know the answer is before we start. We use these easy
problems to begin to learn the basics so that we can solve harder problems. As an example,
the following print function all is using hard-coding:
base10 = 128
print(“128 GB hard disk”)
The following print function call is not using hard-coding:
base10 = 128
print(base10, “GB hard disk”)
Of course, we need to hard-code the value for the initial variable for now until we learn how
to write code that asks the user to type in values.
To complete Checkpoint 3: When you are convinced your program is correct, show
it to a TA or a mentor. Your program should have only three variables and should not use
hard-code values.
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