http://www.cplusplus.com/files/tutorial.pdf
TUTORIAL DASAR C++ IN ENGLISH LANGUAGE
Basics of C++
Structure of a program
Probably the best way to start learning a programming language is by writing a program. Therefore, here is our
first program:
// my first program in C++
#include <iostream>
using namespace std;
int main ()
{
cout << "Hello World!";
return 0;
}
Hello World!
The first panel shows the source code for our first program. The second one shows the result of the program once
compiled and executed. The way to edit and compile a program depends on the compiler you are using. Depending
on whether it has a Development Interface or not and on its version. Consult the compilers section and the manual
or help included with your compiler if you have doubts on how to compile a C++ console program.
The previous program is the typical program that programmer apprentices write for the first time, and its result is
the printing on screen of the "Hello World!" sentence. It is one of the simplest programs that can be written in
C++, but it already contains the fundamental components that every C++ program has. We are going to look line
by line at the code we have just written:
// my first program in C++
This is a comment line. All lines beginning with two slash signs (//) are considered comments and do not
have any effect on the behavior of the program. The programmer can use them to include short
explanations or observations within the source code itself. In this case, the line is a brief description of
what our program is.
#include <iostream>
Lines beginning with a hash sign (#) are directives for the preprocessor. They are not regular code lines
with expressions but indications for the compiler's preprocessor. In this case the directive #include
<iostream> tells the preprocessor to include the iostream standard file. This specific file (iostream)
includes the declarations of the basic standard input-output library in C++, and it is included because its
functionality is going to be used later in the program.
using namespace std;
All the elements of the standard C++ library are declared within what is called a namespace, the
namespace with the name std. So in order to access its functionality we declare with this expression that
we will be using these entities. This line is very frequent in C++ programs that use the standard library,
and in fact it will be included in most of the source codes included in these tutorials.
int main ()
This line corresponds to the beginning of the definition of the main function. The main function is the point
by where all C++ programs start their execution, independently of its location within the source code. It
does not matter whether there are other functions with other names defined before or after it - the
instructions contained within this function's definition will always be the first ones to be executed in any
C++ program. For that same reason, it is essential that all C++ programs have a main function.
The word main is followed in the code by a pair of parentheses (()). That is because it is a function
declaration: In C++, what differentiates a function declaration from other types of expressions are these
parentheses that follow its name. Optionally, these parentheses may enclose a list of parameters within
them.
Right after these parentheses we can find the body of the main function enclosed in braces ({}). What is
contained within these braces is what the function does when it is executed.
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cout << "Hello World!";
This line is a C++ statement. A statement is a simple or compound expression that can actually produce
some effect. In fact, this statement performs the only action that generates a visible effect in our first
program.
cout represents the standard output stream in C++, and the meaning of the entire statement is to insert
a sequence of characters (in this case the Hello World sequence of characters) into the standard output
stream (which usually is the screen).
cout is declared in the iostream standard file within the std namespace, so that's why we needed to
include that specific file and to declare that we were going to use this specific namespace earlier in our
code.
Notice that the statement ends with a semicolon character (;). This character is used to mark the end of
the statement and in fact it must be included at the end of all expression statements in all C++ programs
(one of the most common syntax errors is indeed to forget to include some semicolon after a statement).
return 0;
The return statement causes the main function to finish. return may be followed by a return code (in our
example is followed by the return code 0). A return code of 0 for the main function is generally interpreted
as the program worked as expected without any errors during its execution. This is the most usual way to
end a C++ console program.
You may have noticed that not all the lines of this program perform actions when the code is executed. There were
lines containing only comments (those beginning by //). There were lines with directives for the compiler's
preprocessor (those beginning by #). Then there were lines that began the declaration of a function (in this case,
the main function) and, finally lines with statements (like the insertion into cout), which were all included within
the block delimited by the braces ({}) of the main function.
The program has been structured in different lines in order to be more readable, but in C++, we do not have strict
rules on how to separate instructions in different lines. For example, instead of
int main ()
{
cout << " Hello World!";
return 0;
}
We could have written:
int main () { cout << "Hello World!"; return 0; }
All in just one line and this would have had exactly the same meaning as the previous code.
In C++, the separation between statements is specified with an ending semicolon (;) at the end of each one, so
the separation in different code lines does not matter at all for this purpose. We can write many statements per
line or write a single statement that takes many code lines. The division of code in different lines serves only to
make it more legible and schematic for the humans that may read it.
Let us add an additional instruction to our first program:
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// my second program in C++
#include <iostream>
using namespace std;
int main ()
{
cout << "Hello World! ";
cout << "I'm a C++ program";
return 0;
}
Hello World! I'm a C++ program
In this case, we performed two insertions into cout in two different statements. Once again, the separation in
different lines of code has been done just to give greater readability to the program, since main could have been
perfectly valid defined this way:
int main () { cout << " Hello World! "; cout << " I'm a C++ program "; return 0; }
We were also free to divide the code into more lines if we considered it more convenient:
int main ()
{
cout <<
"Hello World!";
cout
<< "I'm a C++ program";
return 0;
}
And the result would again have been exactly the same as in the previous examples.
Preprocessor directives (those that begin by #) are out of this general rule since they are not statements. They are
lines read and processed by the preprocessor and do not produce any code by themselves. Preprocessor directives
must be specified in their own line and do not have to end with a semicolon (;).
Comments
Comments are parts of the source code disregarded by the compiler. They simply do nothing. Their purpose is only
to allow the programmer to insert notes or descriptions embedded within the source code.
C++ supports two ways to insert comments:
// line comment
/* block comment */
The first of them, known as line comment, discards everything from where the pair of slash signs (//) is found up
to the end of that same line. The second one, known as block comment, discards everything between the /*
characters and the first appearance of the */ characters, with the possibility of including more than one line.
We are going to add comments to our second program:
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/* my second program in C++
with more comments */
#include <iostream>
using namespace std;
int main ()
{
cout << "Hello World! "; // prints Hello
World!
cout << "I'm a C++ program"; // prints I'm a
C++ program
return 0;
}
Hello World! I'm a C++ program
If you include comments within the source code of your programs without using the comment characters
combinations //, /* or */, the compiler will take them as if they were C++ expressions, most likely causing one or
several error messages when you compile it.
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Variables. Data Types.
The usefulness of the "Hello World" programs shown in the previous section is quite questionable. We had to write
several lines of code, compile them, and then execute the resulting program just to obtain a simple sentence
written on the screen as result. It certainly would have been much faster to type the output sentence by ourselves.
However, programming is not limited only to printing simple texts on the screen. In order to go a little further on
and to become able to write programs that perform useful tasks that really save us work we need to introduce the
concept of variable.
Let us think that I ask you to retain the number 5 in your mental memory, and then I ask you to memorize also
the number 2 at the same time. You have just stored two different values in your memory. Now, if I ask you to add
1 to the first number I said, you should be retaining the numbers 6 (that is 5+1) and 2 in your memory. Values
that we could now for example subtract and obtain 4 as result.
The whole process that you have just done with your mental memory is a simile of what a computer can do with
two variables. The same process can be expressed in C++ with the following instruction set:
a = 5;
b = 2;
a = a + 1;
result = a - b;
Obviously, this is a very simple example since we have only used two small integer values, but consider that your
computer can store millions of numbers like these at the same time and conduct sophisticated mathematical
operations with them.
Therefore, we can define a variable as a portion of memory to store a determined value.
Each variable needs an identifier that distinguishes it from the others, for example, in the previous code the
variable identifiers were a, b and result, but we could have called the variables any names we wanted to invent,
as long as they were valid identifiers.
Identifiers
A valid identifier is a sequence of one or more letters, digits or underscore characters (_). Neither spaces nor
punctuation marks or symbols can be part of an identifier. Only letters, digits and single underscore characters are
valid. In addition, variable identifiers always have to begin with a letter. They can also begin with an underline
character (_ ), but in some cases these may be reserved for compiler specific keywords or external identifiers, as
well as identifiers containing two successive underscore characters anywhere. In no case they can begin with a
digit.
Another rule that you have to consider when inventing your own identifiers is that they cannot match any keyword
of the C++ language nor your compiler's specific ones, which are reserved keywords. The standard reserved
keywords are:
asm, auto, bool, break, case, catch, char, class, 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, operator, 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
Additionally, alternative representations for some operators cannot be used as identifiers since they are reserved
words under some circumstances:
and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq
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Your compiler may also include some additional specific reserved keywords.
Very important: The C++ language is a "case sensitive" language. That means that an identifier written in capital
letters is not equivalent to another one with the same name but written in small letters. Thus, for example, the
RESULT variable is not the same as the result variable or the Result variable. These are three different variable
identifiers.
Fundamental data types
When programming, we store the variables in our computer's memory, but the computer has to know what kind of
data we want to store in them, since it is not going to occupy the same amount of memory to store a simple
number than to store a single letter or a large number, and they are not going to be interpreted the same way.
The memory in our computers is organized in bytes. A byte is the minimum amount of memory that we can
manage in C++. A byte can store a relatively small amount of data: one single character or a small integer
(generally an integer between 0 and 255). In addition, the computer can manipulate more complex data types that
come from grouping several bytes, such as long numbers or non-integer numbers.
Next you have a summary of the basic fundamental data types in C++, as well as the range of values that can be
represented with each one:
Name Description Size* Range*
char Character or small integer. 1byte
signed: -128 to 127
unsigned: 0 to 255
short int
(short)
Short Integer. 2bytes
signed: -32768 to 32767
unsigned: 0 to 65535
int Integer. 4bytes
signed: -2147483648 to
2147483647
unsigned: 0 to 4294967295
long int (long) Long integer. 4bytes
signed: -2147483648 to
2147483647
unsigned: 0 to 4294967295
bool
Boolean value. It can take one of two values: true
or false.
1byte true or false
float Floating point number. 4bytes +/- 3.4e +/- 38 (~7 digits)
double Double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)
long double Long double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)
wchar_t Wide character.
2 or 4
bytes
1 wide character
* The values of the columns Size and Range depend on the system the program is compiled for. The values
shown above are those found on most 32-bit systems. But for other systems, the general specification is that int
has the natural size suggested by the system architecture (one "word") and the four integer types char, short,
int and long must each one be at least as large as the one preceding it, with char being always 1 byte in size.
The same applies to the floating point types float, double and long double, where each one must provide at
least as much precision as the preceding one.
Declaration of variables
In order to use a variable in C++, we must first declare it specifying which data type we want it to be. The syntax
to declare a new variable is to write the specifier of the desired data type (like int, bool, float...) followed by a valid
variable identifier. For example:
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int a;
float mynumber;
These are two valid declarations of variables. The first one declares a variable of type int with the identifier a. The
second one declares a variable of type float with the identifier mynumber. Once declared, the variables a and
mynumber can be used within the rest of their scope in the program.
If you are going to declare more than one variable of the same type, you can declare all of them in a single
statement by separating their identifiers with commas. For example:
int a, b, c;
This declares three variables (a, b and c), all of them of type int, and has exactly the same meaning as:
int a;
int b;
int c;
The integer data types char, short, long and int can be either signed or unsigned depending on the range of
numbers needed to be represented. Signed types can represent both positive and negative values, whereas
unsigned types can only represent positive values (and zero). This can be specified by using either the specifier
signed or the specifier unsigned before the type name. For example:
unsigned short int NumberOfSisters;
signed int MyAccountBalance;
By default, if we do not specify either signed or unsigned most compiler settings will assume the type to be
signed, therefore instead of the second declaration above we could have written:
int MyAccountBalance;
with exactly the same meaning (with or without the keyword signed)
An exception to this general rule is the char type, which exists by itself and is considered a different fundamental
data type from signed char and unsigned char, thought to store characters. You should use either signed or
unsigned if you intend to store numerical values in a char-sized variable.
short and long can be used alone as type specifiers. In this case, they refer to their respective integer
fundamental types: short is equivalent to short int and long is equivalent to long int. The following two
variable declarations are equivalent:
short Year;
short int Year;
Finally, signed and unsigned may also be used as standalone type specifiers, meaning the same as signed int
and unsigned int respectively. The following two declarations are equivalent:
unsigned NextYear;
unsigned int NextYear;
To see what variable declarations look like in action within a program, we are going to see the C++ code of the
example about your mental memory proposed at the beginning of this section:
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// operating with variables
#include <iostream>
using namespace std;
int main ()
{
// declaring variables:
int a, b;
int result;
// process:
a = 5;
b = 2;
a = a + 1;
result = a - b;
// print out the result:
cout << result;
// terminate the program:
return 0;
}
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Do not worry if something else than the variable declarations themselves looks a bit strange to you. You will see
the rest in detail in coming sections.
Scope of variables
All the variables that we intend to use in a program must have been declared with its type specifier in an earlier
point in the code, like we did in the previous code at the beginning of the body of the function main when we
declared that a, b, and result were of type int.
A variable can be either of global or local scope. A global variable is a variable declared in the main body of the
source code, outside all functions, while a local variable is one declared within the body of a function or a block.
Global variables can be referred from anywhere in the code, even inside functions, whenever it is after its
declaration.
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The scope of local variables is limited to the block enclosed in braces ({}) where they are declared. For example, if
they are declared at the beginning of the body of a function (like in function main) their scope is between its
declaration point and the end of that function. In the example above, this means that if another function existed in
addition to main, the local variables declared in main could not be accessed from the other function and vice versa.
Initialization of variables
When declaring a regular local variable, its value is by default undetermined. But you may want a variable to store
a concrete value at the same moment that it is declared. In order to do that, you can initialize the variable. There
are two ways to do this in C++:
The first one, known as c-like, is done by appending an equal sign followed by the value to which the variable will
be initialized:
type identifier = initial_value ;
For example, if we want to declare an int variable called a initialized with a value of 0 at the moment in which it is
declared, we could write:
int a = 0;
The other way to initialize variables, known as constructor initialization, is done by enclosing the initial value
between parentheses (()):
type identifier (initial_value) ;
For example:
int a (0);
Both ways of initializing variables are valid and equivalent in C++.
// initialization of variables
#include <iostream>
using namespace std;
int main ()
{
int a=5; // initial value = 5
int b(2); // initial value = 2
int result; // initial value
undetermined
a = a + 3;
result = a - b;
cout << result;
return 0;
}
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Introduction to strings
Variables that can store non-numerical values that are longer than one single character are known as strings.
The C++ language library provides support for strings through the standard string class. This is not a
fundamental type, but it behaves in a similar way as fundamental types do in its most basic usage.
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A first difference with fundamental data types is that in order to declare and use objects (variables) of this type we
need to include an additional header file in our source code: <string> and have access to the std namespace
(which we already had in all our previous programs thanks to the using namespace statement).
// my first string
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string mystring = "This is a string";
cout << mystring;
return 0;
}
This is a string
As you may see in the previous example, strings can be initialized with any valid string literal just like numerical
type variables can be initialized to any valid numerical literal. Both initialization formats are valid with strings:
string mystring = "This is a string";
string mystring ("This is a string");
Strings can also perform all the other basic operations that fundamental data types can, like being declared without
an initial value and being assigned values during execution:
// my first string
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string mystring;
mystring = "This is the initial string content";
cout << mystring << endl;
mystring = "This is a different string content";
cout << mystring << endl;
return 0;
}
This is the initial string content
This is a different string content
For more details on C++ strings, you can have a look at the string class reference.
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Constants
Constants are expressions with a fixed value.
Literals
Literals are used to express particular values within the source code of a program. We have already used these
previously to give concrete values to variables or to express messages we wanted our programs to print out, for
example, when we wrote:
a = 5;
the 5 in this piece of code was a literal constant.
Literal constants can be divided in Integer Numerals, Floating-Point Numerals, Characters, Strings and Boolean
Values.
Integer Numerals
1776
707
-273
They are numerical constants that identify integer decimal values. Notice that to express a numerical constant we
do not have to write quotes (") nor any special character. There is no doubt that it is a constant: whenever we
write 1776 in a program, we will be referring to the value 1776.
In addition to decimal numbers (those that all of us are used to use every day) C++ allows the use as literal
constants of octal numbers (base 8) and hexadecimal numbers (base 16). If we want to express an octal number
we have to precede it with a 0 (zero character). And in order to express a hexadecimal number we have to precede
it with the characters 0x (zero, x). For example, the following literal constants are all equivalent to each other:
75 // decimal
0113 // octal
0x4b // hexadecimal
All of these represent the same number: 75 (seventy-five) expressed as a base-10 numeral, octal numeral and
hexadecimal numeral, respectively.
Literal constants, like variables, are considered to have a specific data type. By default, integer literals are of type
int. However, we can force them to either be unsigned by appending the u character to it, or long by appending l:
75 // int
75u // unsigned int
75l // long
75ul // unsigned long
In both cases, the suffix can be specified using either upper or lowercase letters.
Floating Point Numbers
They express numbers with decimals and/or exponents. They can include either a decimal point, an e character
(that expresses "by ten at the Xth height", where X is an integer value that follows the e character), or both a
decimal point and an e character:
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3.14159 // 3.14159
6.02e23 // 6.02 x 10^23
1.6e-19 // 1.6 x 10^-19
3.0 // 3.0
These are four valid numbers with decimals expressed in C++. The first number is PI, the second one is the
number of Avogadro, the third is the electric charge of an electron (an extremely small number) -all of them
approximated- and the last one is the number three expressed as a floating-point numeric literal.
The default type for floating point literals is double. If you explicitly want to express a float or long double
numerical literal, you can use the f or l suffixes respectively:
3.14159L // long double
6.02e23f // float
Any of the letters that can be part of a floating-point numerical constant (e, f, l) can be written using either lower
or uppercase letters without any difference in their meanings.
Character and string literals
There also exist non-numerical constants, like:
'z'
'p'
"Hello world"
"How do you do?"
The first two expressions represent single character constants, and the following two represent string literals
composed of several characters. Notice that to represent a single character we enclose it between single quotes (')
and to express a string (which generally consists of more than one character) we enclose it between double quotes
(").
When writing both single character and string literals, it is necessary to put the quotation marks surrounding them
to distinguish them from possible variable identifiers or reserved keywords. Notice the difference between these
two expressions:
x
'x'
x alone would refer to a variable whose identifier is x, whereas 'x' (enclosed within single quotation marks) would
refer to the character constant 'x'.
Character and string literals have certain peculiarities, like the escape codes. These are special characters that are
difficult or impossible to express otherwise in the source code of a program, like newline (\n) or tab (\t). All of
them are preceded by a backslash (\). Here you have a list of some of such escape codes:
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\n newline
\r carriage return
\t tab
\v vertical tab
\b backspace
\f form feed (page feed)
\a alert (beep)
\' single quote (')
\" double quote (")
\? question mark (?)
\\ backslash (\)
For example:
'\n'
'\t'
"Left \t Right"
"one\ntwo\nthree"
Additionally, you can express any character by its numerical ASCII code by writing a backslash character (\)
followed by the ASCII code expressed as an octal (base-8) or hexadecimal (base-16) number. In the first case
(octal) the digits must immediately follow the backslash (for example \23 or \40), in the second case
(hexadecimal), an x character must be written before the digits themselves (for example \x20 or \x4A).
String literals can extend to more than a single line of code by putting a backslash sign (\) at the end of each
unfinished line.
"string expressed in \
two lines"
You can also concatenate several string constants separating them by one or several blank spaces, tabulators,
newline or any other valid blank character:
"this forms" "a single" "string" "of characters"
Finally, if we want the string literal to be explicitly made of wide characters (wchar_t), instead of narrow characters
(char), we can precede the constant with the L prefix:
L"This is a wide character string"
Wide characters are used mainly to represent non-English or exotic character sets.
Boolean literals
There are only two valid Boolean values: true and false. These can be expressed in C++ as values of type bool by
using the Boolean literals true and false.
Defined constants (#define)
You can define your own names for constants that you use very often without having to resort to memoryconsuming
variables, simply by using the #define preprocessor directive. Its format is:
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#define identifier value
For example:
#define PI 3.14159
#define NEWLINE '\n'
This defines two new constants: PI and NEWLINE. Once they are defined, you can use them in the rest of the code
as if they were any other regular constant, for example:
// defined constants: calculate circumference
#include <iostream>
using namespace std;
#define PI 3.14159
#define NEWLINE '\n'
int main ()
{
double r=5.0; // radius
double circle;
circle = 2 * PI * r;
cout << circle;
cout << NEWLINE;
return 0;
}
31.4159
In fact the only thing that the compiler preprocessor does when it encounters #define directives is to literally
replace any occurrence of their identifier (in the previous example, these were PI and NEWLINE) by the code to
which they have been defined (3.14159 and '\n' respectively).
The #define directive is not a C++ statement but a directive for the preprocessor; therefore it assumes the entire
line as the directive and does not require a semicolon (;) at its end. If you append a semicolon character (;) at the
end, it will also be appended in all occurrences within the body of the program that the preprocessor replaces.
Declared constants (const)
With the const prefix you can declare constants with a specific type in the same way as you would do with a
variable:
const int pathwidth = 100;
const char tabulator = '\t';
Here, pathwidth and tabulator are two typed constants. They are treated just like regular variables except that
their values cannot be modified after their definition.
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Operators
Once we know of the existence of variables and constants, we can begin to operate with them. For that purpose,
C++ integrates operators. Unlike other languages whose operators are mainly keywords, operators in C++ are
mostly made of signs that are not part of the alphabet but are available in all keyboards. This makes C++ code
shorter and more international, since it relies less on English words, but requires a little of learning effort in the
beginning.
You do not have to memorize all the content of this page. Most details are only provided to serve as a later
reference in case you need it.
Assignment (=)
The assignment operator assigns a value to a variable.
a = 5;
This statement assigns the integer value 5 to the variable a. The part at the left of the assignment operator (=) is
known as the lvalue (left value) and the right one as the rvalue (right value). The lvalue has to be a variable
whereas the rvalue can be either a constant, a variable, the result of an operation or any combination of these.
The most important rule when assigning is the right-to-left rule: The assignment operation always takes place from
right to left, and never the other way:
a = b;
This statement assigns to variable a (the lvalue) the value contained in variable b (the rvalue). The value that was
stored until this moment in a is not considered at all in this operation, and in fact that value is lost.
Consider also that we are only assigning the value of b to a at the moment of the assignment operation. Therefore
a later change of b will not affect the new value of a.
For example, let us have a look at the following code - I have included the evolution of the content stored in the
variables as comments:
// assignment operator
#include <iostream>
using namespace std;
int main ()
{
int a, b; // a:?, b:?
a = 10; // a:10, b:?
b = 4; // a:10, b:4
a = b; // a:4, b:4
b = 7; // a:4, b:7
cout << "a:";
cout << a;
cout << " b:";
cout << b;
return 0;
}
a:4 b:7
This code will give us as result that the value contained in a is 4 and the one contained in b is 7. Notice how a was
not affected by the final modification of b, even though we declared a = b earlier (that is because of the right-toleft
rule).
