C++ - Tutorial 001. Hello World

C++, Hello World

The minimum program in C ++ is

int main() { } // the minimal C++ program

In this program, the declaration of the main function is presented, which takes no arguments. The curly brackets reflect grouping in C++ and in this case show the body of the main function. That is, the beginning of the main function is the opening parenthesis, and the end of the main function is the closing parenthesis. A double slash shows the beginning of the comment. Comments are ignored by the compiler and serve to refine the information in the code.

Each program written in C++ has the function main() , with which the program starts. The main() function, as a rule, returns the result of its execution, which is indicated by the int (integer) data type written before the main() function. If the function is successful, the main() function returns 0 as the result. The value of the result, other than zero, signals an abnormal termination of the program.

The value returned by the program upon completion can be used in the operating system for service purposes.

A typical example of the first program in any programming language is the output of the text "Hello, World!" :

#include <iostream>

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

But is it so simple in this program? In general, already this one small program carries a very large layer of information, which must be understood for development in C++.

  1. #include directive
    #include <iostream>
    tells the compiler that it is necessary to connect a header file, the components of which are planned to be used in the file where the main() function is declared. iostream is a standard input library from STL. That is, the functional of libraries is already used here, although it is the standard for the language. And the last point is the angle brackets, in which the name of the library is located, which say that this is the inclusion of external files in the project, and not those that are part of the project. The same files that are included in the project are connected by enclosing them in normal quotes, for example #include "myclass.h" . This library connection is standard. For example, in Visual Studio , if this standard is not followed, errors will occur.
  2. std is the use of the namespace in which the cout output statement is located. Namespaces were introduced in C ++ in order to remove name conflicts between libraries and the developer's project, if there are repeated names of functions or classes somewhere. In Java, the package system is used to resolve name conflicts.

  3. cout is an output operator that has an overloaded operator << , in order not to use a separate function to output text to the console.

This is in addition to the fact that the record of the main function can have a different form, although the standard is two records:

  1. int main()
  2. int main(int argc, char* argv[])

You can find more records like void main() , etc. But these are erroneous records, although in some compilers they will be compiled, even without errors and warnings.

In the record int main (int argc, char * argv []) arguments are passed:

  1. argc - indicates the number of arguments passed. Always at least 1, because the name of the program is always passed
  2. argv[] - an array of pointers to arguments that are passed as string variables.

If argc is greater than 1, then additional arguments were passed when the program was started.

The check can look like this:

#include <iostream>
 
int main(int argc, char* argv[])
{
    // If an additional argument is passed,
    if (argc > 1)
    {
        // Then try to derive the argument
        std::cout << argv[1]<<endl;
    } 
    else
    {
        // Otherwise, we inform you that the arguments were not transmitted
        cout << "Without arguments" << endl;
    }
    return 0;
}

In general, there are a lot of things that you need to understand in C ++, even for a small program, but this is only more interesting ;-)

We recommend hosting TIMEWEB
We recommend hosting TIMEWEB
Stable hosting, on which the social network EVILEG is located. For projects on Django we recommend VDS hosting.
Support the author Donate

Comments

Only authorized users can post comments.
Please, Log in or Sign up
How to become an author?

Contribute to the evolution of the EVILEG community.

Learn how to become a site author.

Learn it
Donate

Good day, Dear Users!!!

I am Evgenii Legotckoi, developer of EVILEG. And it is my hobby project, which helps to learn programming another programmers and developers

If the site helped you, and you want also support the development of the site, than you can donate by following ways

PayPalYandex.Money
Timeweb

Let me recommend you the excellent hosting on which EVILEG is located.

For many years, Timeweb has been proving his stability.

For projects on Django I recommend VDS hosting

View Hosting Timeweb
AS
May 26, 2020, 11:29 a.m.
Artem Sun-Dun-Chan

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:50points,
  • Rating points-4
MN
May 25, 2020, 11:33 a.m.
Mitja Nagibin

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:50points,
  • Rating points-4
f
May 25, 2020, 5:05 a.m.
falcon

C++ - Test 001. The first program and data types

  • Result:66points,
  • Rating points-1
Last comments
AL
May 29, 2020, 5:24 a.m.
Aleksandr Leonidov

Django - Tutorial 036. How to add authentication through social networks. VKontakte

Здравствуйте! После клика на ссылку авторизации выдает json словарь с ошибкой: {"error":"invalid_request","error_description":"redirect_uri is incorrect, check application redirect uri in …
May 28, 2020, 3:14 p.m.
Evgenij Legotskoj

Qt/C++ - Lesson 039. How to paint stroke in QSqlTableModel by value in the column?

Ну в моём примере, который в статье сработало так model->setData(model->index(1, 1), 7); Поскольку model->index(1, 0) - это индекс колонки id, которая скрыта, поэтому…
MA
May 28, 2020, 3:08 p.m.
Mihail A

Qt/C++ - Lesson 039. How to paint stroke in QSqlTableModel by value in the column?

Спасибо, завтра првоерю. А model->setData(model->index(1, 0), 7); Тоже заработало?
May 28, 2020, 3:06 p.m.
Evgenij Legotskoj

Qt/C++ - Lesson 039. How to paint stroke in QSqlTableModel by value in the column?

Да, метод data всё-таки влиял, я переписал его так и заработало удаление QVariant TableModel::data(const QModelIndex &idx, int role) const{ if (role == Qt::BackgroundColorRole) {…
May 28, 2020, 2:49 p.m.
Evgenij Legotskoj

Django - Tutorial 011. Adding comments to the site based on Django

Он более функциональный и его функционал объективно лучше поддерживается Django. Из первого, что приходит на ум: Это наличие полей типа Array Поддержка полей для JSON …
Now discuss on the forum
IP
May 29, 2020, 1:55 a.m.
Igor' Poroshin

QTablwView + QSqlQueryModel скрыть пустой столбец

Да, понятно. В данном случае лучше использовать серверную процедуру (если такие поддерживаются), в которой будет проверяться наличие всех пустых строк у нужного столбца и вызываться соответ…
RG
May 28, 2020, 6:21 p.m.
Rovshan Gurbanov

Сборка под старые версии Android

У меня SDK почти все версии есть, NDK есть версии 10, 17, 21. Но собирается приложение только с NDK v21 под Android версии 7.0 и выше Версия Qt у меня 5.14.2
May 28, 2020, 7:58 a.m.
Evgenij Legotskoj

Освобождение памяти QMainWindow::setCentralWidget

Да, соглашусь. Просто удаление происходит позже, а не сразу.
May 28, 2020, 5:43 a.m.
Mihailll

При подключении к git как указать пароль?

Нужно сделать ssh-keygen и потом полученый из файла код скопировать в ssh ключ в бикбакете
F
May 28, 2020, 1:42 a.m.
Fidan

QML

Да, проблема ушла, спасибо.
About
Services
© EVILEG 2015-2020
Recommend hosting TIMEWEB