Lab 0: C Warm-Up And Preview

Overview

• Set up your computing environment for the rest of the quarter.
• Compile and run C code on a Linux environment.
• Observe C programming behaviors that will preview the topics covered in the later labs.

Be sure to read the Linux tips page to set up your environment and pick a text editor before starting this lab.
Instructions on what to do are in the Canvas quiz along with comments in the starter code.

Code for this lab

Get the code you need via one of these methods:

• Browser (click to download): lab0.c
• Terminal: wget https://courses.cs.washington.edu/courses/cse351/18sp/labs/lab0.c

Instructions

Editing Code

After acquiring the source file, you will need to open lab0.c in your text editor of choice. See the tutorials if you are unsure how to make edits.

The lab0.c file contains a number of comments explaining some basics of C (and their differences from Java). There are five different parts to this lab and you will need to modify or write some lines of code for each one. We recommend keeping an unmodified copy of lab0.c around for reference (as you may lose track of all the changes you end up making).

Compiling Code

The source file lab0.c won't do anything by itself; you need a compiler (specifically the GNU C compiler) to generate to an executable from it. The GNU C compiler is available on the CSE VM, attu, the instructional Linux machines in the CSE undergraduate lab, and most popular variants of Linux, such as Ubuntu and Fedora. You are free to use whichever machine you like, although we will provide support only for the CSE home VM, attu, and the instructional Linux machines in the lab.

Using any one of these machines, open a terminal and execute gcc -v. On attu, we see:

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/rh/devtoolset-4/root/usr/libexec/gcc/x86_64-redhat-linux/5.3.1/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,lto --prefix=/opt/rh/devtoolset-4/root/usr --mandir=/opt/rh/devtoolset-4/root/usr/share/man --infodir=/opt/rh/devtoolset-4/root/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --enable-plugin --with-linker-hash-style=gnu --enable-initfini-array --disable-libgcj --with-default-libstdcxx-abi=gcc4-compatible --with-isl=/builddir/build/BUILD/gcc-5.3.1-20160406/obj-x86_64-redhat-linux/isl-install --enable-libmpx --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 5.3.1 20160406 (Red Hat 5.3.1-6) (GCC)

The output tells me a bunch of the configuration options for the my installation of GCC as well as the version number, which is 5.3.1. Assuming that you have saved lab0.c somewhere on your machine, navigate to that directory, and then use GCC to compile it with the following command:

$ gcc -g -Wall -std=gnu99 -o lab0 lab0.c

It's not that important right now for you to know what all of these options do, but -g tells the compiler to include debugging symbols, -Wall says to print warnings for all types of potential problems, -std=gnu99 says to use the C99 standard (now only 18 years old!), -o lab0 instructs the compiler to output the executable code to a file called lab0, and lab0.c is the source file being compiled.

During execution of that command, you should see a warning about the variable 'bigArray', which you can safely ignore. This warning would not be shown if you removed -Wall from the gcc command, but you will want -Wall to catch potential errors when you write code yourself.

Having executed the gcc command, you should be able to see a file named lab0 in the same directory:

$ ls
lab0  lab0.c

Running Executables

The lab0 file is an executable file, which you can run using the command ./lab0. You should see:

$ ./lab0
Usage: ./lab0 <num>

In this case, the executable lab0 is expecting a command-line argument, which is text that is provided to the executable from the command-line when the program is run. In particular, lab0 wants a number from 1 to 5, corresponding to which part of the lab code you want to run. See main() in lab0.c for more details. For example:

$ ./lab0 1
*** LAB 0 PART 1 ***
x = 351
y = 410
x & x = 351

Checking Your Work

With that, you should have everything you need to complete the assignment. Follow the instructions found on the associated Canvas quiz; you will want to work on the different parts of the lab in order (from 1 to 5). Each question can be answered and/or verified by appropriate edits to the source code. Note that every time you want to test a code modification, you will need to use the gcc -g -Wall -std=gnu99 -o lab0 lab0.c command to produce an updated lab0 executable file (Tip: Use the up and down keys to scroll through previous commands you've executed).

You can submit the Lab 0 quiz once you have answered all of the questions. Canvas will indicate which questions were answered correctly and which were answered incorrectly. You have a maximum of 20 submissions.

Some of the code behaviors will seem inexplicable at this point, but our goal is that you will be able to explain to someone else what is going on by the end of this course! =)

Submission

You will not be submitting files for this lab. Submit your answers to the Lab 0 Canvas quiz.