lect02, Thu 01/10

Hello World! + unix, vim and git

Basic Unix Commands

In the displayed commands, don’t include brackets. E.g., mkdir [name] will look like mkdir tmp, if you want to create a directory called tmp.

pwd used to print the working directory - displays the full path

ls lists the contents of a directory; if no directory is specified, it will list the contents of the current directory

ls -l lists the contents of a directory, and provides additional information about the file/directory; distinguishes between files and directories (if the line starts with the letter ‘d’, then it corresponds to a directory, if not, then it corresponds to a file)

mv [src] [dest] move a file/directory called src to a file/directory called src

rm [file] deletes/removes a file (use with caution because it deletes files irrecoverably)

rm -r [dir] recursively deletes the contents of a directory ; if you use only rm for a directory, the operating system will complain and display the error message: cannot remove [dir]: Is a directory

mkdir [name] make a new directory called name

mkdir -p [level1/level2/...] allows you to create a series of nested directories

cd used to change directory you are currently located in

~ refers to the home directory

.. refers to the directory above the current one

cd .. goes to the directory above the current one

cd ~ goes to the home directory

./[name] used to execute a compiled program

Vim Commands

The link below is a very useful guide to learn fundamental commands in Vim (most of these were shown in lecture on January 10th):

https://ucsb-cs16.github.io/topics/vim_basic_eight/

Topics

• Programming in the unix environment
• The vim (editor) survival skills
• Writing, compiling and running a C++ program (hello world) program
• Breaking down the hello world program
• Code anywhere and everywhere with git

Programming in the unix environment

• Unix is an operating system just like Windows and Mac OS
• All your data and programs are stored in files, within the unix filesystem
• File vs. directory
• Files are organized within the unix filesystem
• You can navigate the filesystem with some simple commands inside a terminal:
  • ls
  • mv
  • cp
  • pwd
  • mkdir
  • cd
• Relative path vs. absolute path (important for mv, cp, mkdir, cd)

vim Editor

• We will use vim for the first few weeks this quarter.
• Important to be comfortable with a Unix-based command-line text editor.
• Be sure to understand how to do the basic eight functions.

Writing, compiling and running a C++ program (hello world) program

// hello.cpp
#include <iostream>

using namespace std;

int main() {
	cout << "Hello CS 16!" << endl;
	return 0;
}

• Compile and execute the program

$ g++ -o hello hello.cpp
$ ./hello
Hello CS 16!
$

• g++ is one of several C++ compilers
  • Compilers translate “source code” (i.e., the contents in the .cpp file) into a lower-level representation that is easier for computer system hardware to understand.
• -o is a “flag” that instructs the g++ compiler to produce an executable file called hello
• hello.cpp is the source file for g++ to use when producing the executable file.
• In order to actually run an executable file in Unix, ./[filename] is used.

Breaking down the Hello World Program

// hello.cpp
#include <iostream>

using namespace std;

int main() {
	cout << "Hello CS 16!" << endl;
	return 0;
}

#include <iostream>

• This line (also known as an include directive) tells our C++ program to include a library dealing with Input/Output (I/O) functionality.
  • We need the library <iostream> to print stuff to our terminal.

using namespace std;

• This line allows us to use parts of the iostream library without having to prepend std::.
  • For more context, std is short for “standard”.
  • including libraries between angle brackets (< >) imply that this is part of the C++ Standard Library, which is part of the C++ language specification.

int main() { ... }

• The main function. Every C++ program needs to have one main function as its “starting point”.

cout << "Hello CS 16!" << endl;

• cout << [some_value] tells the program to display some_value to the terminal.
• << endl; tells the program to insert a newline at the end.
  • This places the next values to be written on the next line in the terminal.

return 0;

• Since main must be declared to return a value of “int” type, we are simply returning 0.
  • May get more into the relevance of this later.

Comments

• Any commented text will be ignored by the compiler.
• Important to comment code for communication with others working with your code!
• // denotes a single-line comment.
• /* */ denotes a multi-line comment.