Lab01 - Introduction to the Computer Laboratory and C Programming Language

• Introduction to the computer environment - password settings
• Introduction to the working environment - terminal control and elementary commands: ls, cd, pwd, mkdir, cp, mv, rm, touch, and man, cat, find, grep, wget, unzip, echo, and input/output modificators: |, >, ».
• Compile the first program
• Test the executed program
• Become familiar with your selected favorite editor for editing sources, e.g., gedit, Sublime Text, Emacs, Vim.

reference solutions

Exercise 1

Simple program to output text:

#include <stdio.h>

int main()
{
    //this line is a comment, it will be ignored
    printf("Hello World!");
    return 0;
    /*this is
    multiline comment
    */
}

Practice compiling it:

clang myprogram.c

Clang will take your code and produce a binary executable from it. See if you can figure out:

How to customise your executable filename from clang? Make it format correctly in the terminal.

$\qquad\bullet\,$ Hint (click to view)

clang main.c -o <output name>

Exercise 2

We can use printf(“here is an integer: %i”, myint); to format an integer. Similarly %f to format a float.

We can use scanf(“%f”, &fnum); to get a variable from the command line user.

Implement a function that calculates the Euclidean distance of a point $(a,b)$ from the origin $(0,0)$. That is, it takes two numbers ($a$ and $b$), squares each of them, adds them, and returns the square root.

• Hint 1: use sqrt() function from math.h library
• Hint 2: when compiling, link the math library with the -lm compilation flag

Exercise 3

To obtain access to command-line arguments, we must define main function with two parameters, usually named argc (argument count) and argv (argument vector):

#include <stdio.h>

int main(int argc, char *argv[])
{
    printf("The program got %d command-line arguments", argc);
    return 0;
}

Compile the code and run it with three command-line arguments:

./myprogram hello cpl 2025

How many command-line arguments did the program get? Does it correspond with the number of arguments you gave to it?

Try to access the command-line arguments and print them to standard output (use %s to format a string).

Open terminal: Ctrl + Alt + T

New tab: Ctrl + Shift + T

End programs by running: Ctrl+C

Close by: Ctrl + D

Manual to (almost) every terminal program can be found using man:

$ man <program>

You shoud start working in linux terminal by asking, how to use manual

$ man man

To find out, where are you in the directory tree, the present working directory, use pwd:

$ pwd

To list files in your directory, use ls:

$ ls

There is also possibility to see a content of different directory

$ ls <relative/absolute address>

The useful parameters you should know are:

• -a do not ignore entries starting with ., usualy hidden files,
• -A the same as -a but it does not list implied . and ..,
• -l uses a long listing format,
• -p to append / at the end of the name of directories to differentiate them from files,
• you can also sort them by -S size, -t time, etc.,
• and combine them

$ ls -Al

To change the directory use cd:

$ cd <relative/absolute address>

Go to the parent directory

$ cd ..

Go to the parent's parent directory

$ cd ../../

Go to the parent's parent directory and then to its child directory

$ cd ../../some_directory/

Go to the child's child directory

$ some_directory/some_subdirectory/

You can use absolute address:

$ /home/my_account/my_files/my_video/

There is also trivial way to your home directory:

$ cd

The manual is not presented, therefore use parameter –help to find out more

$ cd --help

For fast navigation, use keypad Tab. Use it frequently.

If you want to create a directory, use mkdir:

$ mkdir <directory name>

and touch for file creation:

$ touch <file name>

Please, do not use spaces in your names:

$ mkdir "I have come here from some advertising environment called Windows"
$ mkdir and\ I\ really\ like\ to\ troll

and if necessary, use _ underscore instead:

$ touch I_love_linux 

Use mv for moving files or directories from one position in a directory tree to another:

$ mv <source> <destination>
$ mv random_file.txt ~/random_directory/
$ mv random_directory/ ~/some_directory/some_subdirectory/

Note that character ~ stands for your home directory.

Use mv also for renaming the files:

$ mv obsolete_name much_better_name

Copying files can be done using cp:

$ cp <source> <destination>
$ cp random_file.txt ~/random_directory/
$ cp random_file.txt ~/random_directory/better_name.txt

To copy whole directory, use -r recursive option:

$ cp -r random_directory/ ~/other_directory/some_subdirectory/

You can delete file using rm

$ rm <file name>

Beware! It is very hard to undo!

Deleting whole directory and its content needs -r recursive option:

$ rm -r obsolete_directory/

It is also possible to delete file (or directory) at different position in directory tree:

$ rm ~/random_directory/random_file.txt
$ rm ../../some_system_directory/some_essential_file