Code from lecture

https://github.com/ucsb-cs16-f18-mirza/cs16-f18-lectures/tree/master/lec-02

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.

C++ Variables and Types

• Variables are used to store data.
  • Each variable must have a type associated with it.
    • Not the case in Python where a variable can be anything
  • Variable names must
    • Start with an alphabeticsl character or underscore
    • Other characters can be alphanumeric and underscore characters, but no spaces or other special characters.
  • C++ is case-sensitive. ‘x’ and ‘X’ are considered different variables.
• Some common types:
  • int: Integers
  • double: Floating point
  • char: characters
  • string: sequence (array) of characters
  • bool: boolean
• Good practice to initialize your variables
  • Uninitialized variables may have strange side-effects.

Initializing, Assigning, and Modifying Variables

• Example

int x;      // initialize variable x of type int
int y, z;   // initialize variables x and y in one statement
x = 10;     // assign x to an integer value 10.

int a = 10;   // initialize and assign in one statement
int b = 20, c = 30;

b = 6 + 4;

cout << a << "," << b << "," << c << "," <<
x << "," << y << "," << z << endl;

Code anywhere and everywhere with git

What is git?

• Git is a version control system (VCS). A VCS allows you to keep track of changes in a file (or groups of files) over time
• Git allows you to store code on different computers and keep all these different copies in sync

Why are we learning git in this class?

• Collaborate
• Share code ownership
• Work on larger projects
• Provide feedback on work in progress
• Learn professional software development tools

Git concepts

• repo (short for repository): a place where all your code and its history is stored

• remote repo: The repo created on github.com. You can access a remote repo via a browser (we’ll explore other ways later)

• In class demo:
  • creating a repo on github.com
  • adding collaborators to the repo
  • adding files to the repo
  • Updating files in a remote repo using a web browser
  • Viewing the version history
• cloning a repo: Once you have created a repo, you (and your collaborators) can copy (or clone) it on different computers. Each instance is now a local repo, because it exists on your (local) computer rather than the web.
• Using git command line tools, we can sync up different repos. This means multiple collaborators can work on the same code on different machines.