.. highlight:: c++

Chapter 1 Notes
===============

Please read chapter 1 of the textbook.


Basic Computer Structure
------------------------

see diagram on p. 3 

see diagram on p. 5


Running a Program
-----------------

see diagram on p. 10/11


Creating a Program
------------------

especially for large programs, it is useful to follow a systematic process
when writing programs

see diagram on p. 16


Hello, World in C++
-------------------

::

    // hello_world.cpp

    #include <iostream>
    #include "cmpt_error.h"

    int main() {
        std::cout << "Hello, world!\n";
    }

we call this **source code**, or just **code** for short

programming is all about getting a computer to do things

we will do this mainly by reading and writing C++ source code

the ``//`` characters indicate the beginning of a **source code comment** (or
just **comment**) meant for humans to read

``<iostream>`` is a file in the C++ standard library, and is where ``cout``
resides

the file ``cmpt_error.h`` is special to this course, and contains a function
called ``cmpt::error`` that we will often use; it must be in the same folder
as ``hello_world.cpp``

almost all the programs we write in this course will "include" these two files

all C++ programs must have a ``main`` function

when a C++ program runs, the ``main`` function is always called first


Hello, World in C++
-------------------

``std::cout`` is how we will get C++ to print text on the console

you can think of ``cout`` as the name of the console where text will be
printed

``std`` refers to the standard namespace, which are a group of functions,
variables, classes, etc. pre-defined in the C++ standard library

in the statement ``std::cout << "Hello, world!\n";``, the ``<<`` is like an
arrow indicating that the string ``"Hello, world!\n"`` should be sent to
``std::cout``

the ``\n`` in the string is an **escape character** called **newline** that
represents a line-break

when used with ``std::cout``, it causes the cursor to go to the next line

even though we write ``\n`` using two symbols, ``\`` and ``n``, it represents
a single C++ character


Hello, World in C++
-------------------

notice the ``;`` at the end of the statement

``;`` is a semi-colon, and it is used to mark the end of a statement in C++

also note the matching ``{`` and ``}`` in ``main``

these kinds of brackets are called **curly braces**, or just **braces**

braces are used to make the begin and end of a block of code in C++


Compiling and Running Hello, World
----------------------------------

::

    $ g++ hello_world.cpp
    $ ./a.out
    Hello, world!

``$`` is the Linux command prompt

``g++`` is the particular C++ compiler we are using in this course

the command ``g++ hello_world.cpp`` compiles ``hello_world.cpp``

**compiling** is the process of converting source code (which is in text
format) to an **executable** format (which is binary format) that we can run

by default, ``g++`` names the executable file ``a.out``

to run ``a.out``, Linux requires you put ``./`` in front of the name::

  $ ./a.out 


Compiling and Running Hello, World
----------------------------------

::

    $ g++ -o hello hello_world.cpp
    $ ./hello
    Hello, world!

the ``-o`` option lets you give the executable a friendlier name


Using a makefile
----------------

it turns out that there are other options that are useful to use when
compiling with ``g++``, e.g.

- turning on all possible warnings (to help catch source code errors)

- include debugging info (in case you want to use a debugger)

- stop compiling after the first error

- etc.

::

    $ g++ -o hello -std=c++14 -Wall -Wextra -Werror -Wfatal-errors 
          -Wno-sign-compare -Wnon-virtual-dtor -g hello_world.cpp
    $ ./hello
    Hello, world!


Using a makefile
----------------

instead of typing all these options each time, we store them in file named
``makefile`` and then use the ``make`` command to compile the file

::

    $ make hello_world
    g++  -std=c++14 -Wall -Wextra -Werror -Wfatal-errors -Wno-sign-compare -Wnon-virtual-dtor -g   hello_world.cpp   -o hello_world
    $ ./hello_world 
    Hello, world!

assuming the course ``makefile`` is in the same directory, we just need to
type ``make hello_world`` and ``make`` automatically runs ``g++`` with the
correct options

the executable file name will be the same as the source file name (without 
the ``.cpp``)


Using a makefile
----------------

use the makefile!

it might seem like more work at first, but overall it is a great time-saver
and all those special options will help you catch and prevent errors

``make`` is an entire language, and it is often used with big multi-file
programs; it is a very popular tool

among other things, ``make`` is smart enough to avoid re-compiling files that
have not changed since their last compilation

::

    $ make hello_world
    make: `hello_world' is up to date.

large C++ programs typically consist of 100s, or even 1000s, of files, and so
this feature can save a huge amount of compiling time

if you want to force re-compiling, use the ``-B`` option::

    $ make -B hello_world
    g++  -std=c++14 -Wall -Wextra -Werror -Wfatal-errors -Wno-sign-compare -Wnon-virtual-dtor -g   hello_world.cpp   -o hello_world


A Bigger Program
----------------

::

    // hello_name.cpp

    #include "cmpt_error.h"
    #include <iostream>
    #include <string>

    int main() {
        std::string name;

        std::cout << "What is your name? ";
        std::cin >> name;

        int age = 0;
        std::cout << "How old are you? ";
        std::cin >> age;

        int birth_year = 2017 - age;
        std::cout << "Hi " << name << "!\n"
                  << "Since you are " << age << " years old "
                  << "I'm guessing you were "
                  << "born in " << birth_year << ".\n";
    }

to compile and run this program type

::

    $ make hello_name
    g++  -std=c++14 -Wall -Wextra -Werror -Wfatal-errors -Wno-sign-compare -Wnon-virtual-dtor -g   hello_name.cpp   -o hello_name
    $ ./hello_name

make sure ``cmpt_error.h`` and ``makefile`` are in the same folder!!


The using Command
-----------------

we had to write ``std::`` a lot in the program

for the kinds of small programs we are writing in this course, ``std::``
everywhere makes the source code harder to read

so we will usually add this line to the top of our programs

::

    using namespace std;

this tells C++ to "use" all the names defined in the ``std`` name space in our
program so we don't need to keep writing ``std::``

::

    // hello_name.cpp

    #include "cmpt_error.h"
    #include <iostream>
    #include <string>

    using namespace std;

    int main() {
        string name;

        cout << "What is your name? ";
        cin >> name;

        int age = 0;
        cout << "How old are you? ";
        cin >> age;

        int birth_year = 2017 - age;
        cout << "Hi " << name << "!\n"
             << "Since you are " << age << " years old "
             << "I'm guessing you were "
             << "born in " << birth_year << ".\n";
    }


Things to Note
--------------

C++ is **very** picky about the details of your source code

one wrong character may cause errors

case matters, e.g. ``int`` is not the same as ``Int``

C++ does not usually care about spacing and indentation, but human readers do

thus we will always write our programs in a way that uses indentation and
blank lines to make our code's structure and purpose clearer


Variable Declarations
---------------------

this programs declares three different variables

::

    string name;
    // ...

    int age = 0;
    // ...

    int birth_year = 2017 - age;
    // ...

these are variable **declaration statements**

every C++ variable has a name, and a type (which describes the kind of value
in the variable)

we could have declared ``age`` like this without the ``= 0``

::

    int age;  // bad: initial value of age could be anything

the variable ``age`` has an unknown value!

it could be any ``int``

this sort of uncertainty can be the source of hard-to-detect errors

so it is better to always explicitly initialize variables::

    int age = 0;  // good: initial value of age is 0


Variable Declarations
---------------------

``string`` variables are different

:: 

    string name; // good: name is initialized to the empty string, ""

by default, when you declare a ``string`` variable it is initialized to the
empty string

you could also be explicit and declare ``name`` like this

::

    string name = ""; // good: name is initialized to the empty string, ""

the ``= ""`` is not necessary, but it is good because it makes it a little
clearer exactly what the initial value of ``name`` is