Lab 1: Nice 2 C You

View the lab slides here.

Step 1: Group Work

Welcome to CS 3410! For the first activity of this lab, the TAs will review some of the topics from the first couple of lectures and lead a group activity. Then, you will complete a worksheet with your groups before moving on to setting up your course Docker container and completing a short coding exercise.

There’s no digital material for this part. The TAs will provide the worksheet after the review and icebreaker.

Step 2: Compiling and running C programs

Course Docker Container

Follow these instructions to set up Docker and obtain CS 3410’s Docker container. To summarize, you will need to:

• Install Docker itself.
• Download the image with docker pull ghcr.io/sampsyo/cs3410-infra.
• Consider setting up an rv alias to make the container easy to use.

If you don’t already have a favorite text editor, now would also be a good time to install VSCode.

C Programming

Next, follow these instructions for writing, compiling, and running your first C program.

When your program runs, show the result to a TA. Congratulations! You’re now a C programmer.

Git

Now, we’ll get some experience with Git! If you haven’t already, be sure to follow our guide to setting up your credentials on GitHub so you have an SSH key in place.

Go to the to the Cornell GitHub website and create a repository called “lab1”. This repository can be public, but for assignments all of your repositories must be private.

Next, clone your repository from within a preferred directory on your device:

$ git clone git@github.coecis.cornell.edu:netid/lab1.git

Make sure to replace netid with your actual NetID. If this doesn’t work, ask a TA for assistance. There is probably something wrong with your GitHub configuration.

Before changing directories into the repo, you should move your hi.c file that you created during the Docker setup step into the lab1 folder and clean up the executables we made earlier:

$ mv hi.c lab1
$ rm a.out
$ cd lab1
$ ls

If you haven’t created hi.c or a lab1 folder yet, you can run:

$ mkdir lab1
$ cd lab1
$ printf '#include <stdio.h>\nint main() { printf("hi!\\n"); }\n' > hi.c

You should see the file hi.c in your repository. Enter:

$ git status

The following should appear (or something like it):

On branch main

No commits yet

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        hi.c

Now, you should add the file hi.c to stage it, make a commit, and then push to the remote repository:

$ git add hi.c
$ git commit -m "Initial commit"
$ git push

This is commonly the GitHub workflow for a single person working on an assignment. You’ll make some changes, commit them, and push them, over and over until you finish the assignment.

Step 3: print_digit and print_string

For this next task, you are going to write two helper functions to help you in Assignment 1:

• print_digit(int digit): Given an integer digit between 0 and 15, print digit as a hexadecimal digit using lowercase letters to the terminal (without using printf)
• print_string(char* s): Given a string, print it to the terminal (without using printf)

First, cd into your lab1 repository. Then, make a file called lab1.c, and copy/paste the following code:

#include <stdio.h>

// LAB TASK: Implement print_digit
void print_digit(int digit) {
}

// LAB TASK: Implement print_string
void print_string(char* s) {
}

int main(int argc, char* argv[]) {
  printf("print_digit test: \n"); // Not to use this in A1
  for (int i = 0; i < 16; ++i) {
    print_digit(i);
    fputc(' ', stdout);
  }
  printf("\nprint_string test: \n"); // Not to use this in A1

  char* str = "Hello, 3410\n";
  print_string(str);
  return 0;
}

Save the file and exit the editor. Now is a good time to commit and push your changes to your repository. Once you’ve pushed, try to implement the functions print_digit and print_string. The TAs are available for help should you need it. A good starting point should be to look into the fputc function:

Once you’ve implemented the functions, you can run the program:

$ rv gcc -Wall -Wextra -Wpedantic -Wshadow -std=c17 -o test_lab1 lab1.c
$ rv qemu test_lab1

Remember, if you change lab1.c between runs, you need to recompile the program using the first of the commands above.

At this point, you should check off with a TA so they can check your work. Congrats! You’ve just finished your first lab in CS 3410.