Your First C++ Program

Let’s get right into it. Open Visual Studio (VS), click on New Project… under Start; click Visual C++; Select Empty Project; give the project the name “hello-world” (or whatever); and then click okay. This will build a new project.

Once the project is created, under Solution Explorer (right hand pane), right-click Source Files; Add > New Item…; select Visual C++; C++ File (.cpp); give the file a name (in this case main.cpp or whatever); and click Add. Now you have a new source code file.

The Code

Type the following code into your new file.

Now it is time to compile the source code.

Clicking on the Local Windows Debugger will compile and execute the source code and you should be left with the following window.

Understanding the Code

Now let’s break down the code line by line.

Preprocessor Directive

Line one, #include <iostream>, is called a preprocessor directive. This tells the compiler that an external library needs to be included at compile time. The preprocessor inserts the contents of the file iostream (which is used for input and output functions). This ensure that output functions and operators, like cout, will work.

Namespace

Line two, using namespace std;, is an advanced topic, so we will just introduce the idea here. This allows us to use function from the namespace std without prepending them with a namespace identifier. Basically this makes it so we can display text with cout rather than std::cout. I’ll leave it at that for now.

The Main Function

Line four is the declaration statement of the main function. A function, which we’ll get into in a later lesson, can be thought of as a wrapper for a collection of instructions/statements. In C++ when source code is compiled the starting point of the program is indicated by the main function. Every C++ program should have one main function. The instructions wrapped in a function are also wrapped with curly braces { and }.

int refers to the type of data that is expected to be returned by the function. In this case int is short for integer. So the function is expected to return an integer value back to the operating system on completion of execution.

Output

Line five is responsible for printing the words “Hello world!” to the console screen (the black screen with white text). cout is an object (objects will be covered in a later lesson) that is part of the standard output stream class (classes will be covered in a later lesson as well). cout sends the string of characters (often referred to as a string) following the stream insertion operator (<<) to the console (cout is short for console output). This and operators will be covered more later.

cout is the reason we need to include the iostream external library. Without iostream included, cout does not work because it is not available.

Pausing the System

Line six is a call to a function built into C++. The system function is used to execute commands that are available in the system running below our application (generally an operating system and Windows in this instance). The use of this function here is mostly for convenience since executing this code without displays “Hello world!” to the console and promptly closes the window. The command “pause>nul” causes the operating system to pause execution of the program until some kind of keyboard input is detected, then it will continue executing the program.

“pause>nul” is a DOS command for pausing execution without displaying the default prompt of “Press any key to continue…” that is displayed with just system( “pause” ).

Returning to the System

The last line in the function, line seven, is pretty simple. It returns an integer back to the system/function that called the function (in this case it was Windows that called this program). Since the function main is expected to return an int value back to the OS, we return the value of 0. There will be more on returning values later.

Wrapping up Your First Program

I know the “Hello world” program can be a bit underwhelming. It’s simple and does very little, but it gives a very good foundation to start building on. There is a lot C++ can do, but understanding this most basic of programs, the rest will fall into place.

Lexical Structure

Now that you have some of the basics of programming down, it’s time to dig in and start to understand the basics of the language. The following six sections break down C++’s lexical structure (the letters, symbols, and words that make up the language).

Tokens

A token is the most basic element of any programming language. Tokens fall into five categories identifiers, reserved words, operators, literals, and punctuators.

Identifiers

An identifier is simply a name. Identifiers are used to name variables, functions, objects, classes, structures, arrays, and more.

Identifier Rules

Identifiers must follow specific rules in order to be considered valid by the compiler.

• All characters in the identifier, excluding the first character, must be from the following list (Visual Studio also allows the use of $)
  
  a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 _

  1 2 3 4 5

  a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 _

• The first character cannot be a digit
  
  0 1 2 3 4 5 6 7 8 9

  1	0 1 2 3 4 5 6 7 8 9

• Visual Studio does not have a limit on length of identifiers, but only the first 2,048 characters are significant
  • It’s best to keep identifier names short and to the point
• Uppercase and lowercase letters are distinct, meaning identifiers are case-sensitive
• Cannot be a reserved word

Reserved Words

C++ has reserved words for use by the language often referred to as reserved words or keywords. You cannot use the following words as identifiers. If you do you will most likely encounter errors

C++ Reserved Words

and	and_eq	asm
auto	bitand	bitor
bool	break	case
catch	char	class
compl	const	const_cast
continue	default	delete
do	double	dynamic_cast
else	enum	explicit
export	extern	false
float	for	friend
goto	if	inline
int	long	mutable
namespace	new	not
not_eq	operator	or
or_eq	private	protected
public	register	reinterpret_cast
return	short	signed
sizeof	static	static_cast
struct	switch	template
this	throw	true
try	typedef	typeid
typename	union	unsigned
using	virtual	void
volatile	wchar_t	while
xor	xor_eq

Table 0.1—C++ Reserved Words

Visual Studio Reserved Words

Visual Studio has added more reserved words to this list.

__abstract	__alignof	__asm
__assume	__based	__box
__cdecl	__declspec	__delegate
__event	__except	__fastcall
__finally	__forceinline	__gc
__hook	__identifier	__if_exists
__if_not_exists	__inline	__int16
__int32	__int64	__int8
__interface	__leave	__m128
__m128d	__m128i	__m64
__multiple_inheritance	__nogc	__noop
__pin	__property	__raise
__sealed	__single_inheritance	__stdcall
__super	__try/__except	__try/__finally
__try_cast	__unaligned	__unhook
__uuidof	__value	__virtual_inheritance
__w64	__wchar_t	abstract
alignas	alignof	array
char16_t	char32_t	constexpr
decltype	delegate	deprecated
dllexport	dllimport	event
final	finally	friend_as
gcnew	generic	in
initonly	interface class	interface struct
interior_ptr	literal	naked
noexcept	noinline	noreturn
nothrow	novtable	nullptr
override	property	ref class
ref struct	safecast	sealed
selectany	static_assert	thread
thread_local	using declaration	using directive
uuid	value class	value struct

Table 0.2—Visual Studio Reserved Words

Operators

Operators are used to manipulate data. The best example of operators are arithmetic operators such as addition (+), subtraction (-), multiplication (×), and division (÷). The topic of operators is actually quite vast and will therefore receive it’s own lesson, but we’ll cover some of the basics here.

Arithmetic Operators

If you’ve done any math in your life you should be able to figure out how these work pretty quickly. There are five (yes, five) basic arithmetic operators addition (+), subtraction (-), multiplication (*), division (/), and modulus (%). Modulus is the one that most people are unfamiliar with but the operation lends itself quite nicely to many programming applications. Here is a basic breakdown of the math operators.

Operator	Definition	Example
+	Addition	1 + 2 = 3
-	Subtraction	13 – 8 = 5
*	Multiplication	13.50 * 1.06 = 14.31
/	Division	100 / 5 = 20
%	Modulus	9 % 2 = 1

Table 0.3—Arithmetic Operators

Modulus

Let’s take a moment to look at the modulus operator, since that should be the only operator you may be unfamiliar with. Modulus returns the remainder of division. In the example above

Or if you do it the way I learned in first or second grade (when they didn’t quite want to introduce fractions

The modulus is the remainder value of 1.

Literals

Literals, or constants, are values that appear directly in a program and do not change value during execution. There are four categories of literals used in C++, integers, floating-point, character, and character-strings.

Literal Example	Type	Notes
5	Integer
255	Integer
0x8F	Integer	143 in hexadecimal notation; Hex integers start with “0x”
0452	Integer	298 in octal notation; Octal integers start with “0″
3.14	Floating	Notice the decimal
5.0	Floating	Again with the decimal
6.022e23	Floating	Expressed in scientific notation
‘a’	Character	Must be surrounded by single quotes.
“A lame comment about C++!”	String	Surrounded by double quotes

At this point the purpose of literals may be vague, but in the next lesson, we will cover what they are used for and put them to good use.

Punctuators

With a word like punctuators C++ really starts to sound like a written language. Punctuators help with compilation of code. Just like punctuation in any written language, the symbols help the reader understand the meaning of what is written. Punctuators in C++ do the same thing, they tell the compiler what the coder actually meant as well as giving additional meaning to blocks of code.

The punctuation marks in C++ are

The top line of punctuators are more common than the bottom and punctuators [ ], ( ), and { } always appear in pairs. Most C++ instructions end with a ; (We will discuss exceptions to that rule throughout these lessons).

When looking at the source code of our first program the formatting, line numbers, syntax highlighting, and structure helps us to understand what the code is doing.

However, the compiler sees our code as this

#include<iostream>using namespace std;int main(){cout<<"Hello world!";system("pause>nul");return 0;}

Without the punctuators, the compiler would have a hard time clearly translating the developer’s intention into executable code.

Comments

Comments are segments of text within source code that are ignored by the compiler. This may seem useless at first, but comments are beneficial for developers.

Comments (in orange) come in two varieties block and inline. Block comments usually span several lines, but can be all on one line, and begin with /* and end with */. Everything between /* and */ is ignored by the compiler. Inline comments begin with //. Everything following // to the end of the line is ignored by the compiler.