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C++ Programming Tutorials
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 TechPreparation!";
return 0;
} |
Hello TechPreparation!
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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
TechPreparation!" 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 pound 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.
cout << "Hello
TechPreparation";
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
TechPreparation
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).
NEXT >> return 0;
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