Lesson 1 · 1 of 20

Hello, world · C++

Write your first C++ program: the main() function, std::cout and the << operator to show text and numbers in the console.

C++ · Hello, world in DMarlon Studio: the example's code and its output in the terminal

Every C++ program starts running in the `main()` function. What goes between its braces { } are the statements: they run from top to bottom and each one ends with a semicolon ;.

#include <iostream> brings in the input/output library. With it comes `std::cout`, the console output. The std:: prefix means it belongs to the C++ standard library.

The `<<` operator sends whatever is on its right to std::cout, and it can be chained: "Welcome to " << "C++" << ... builds a single line. Numbers are printed just like text, and 2 + 3 is worked out before it is shown.

To start a new line you can use std::endl or the '\n' character, which also works inside text, as in "Line one\nLine two\n". \t inserts a tab. Comments start with // and the compiler ignores them.

return 0; tells the system that everything went well. In DMarlon Studio, C++ powers native desktop apps with FLTK and the Console target: press F9 to compile and run this example.

Code · main.cpp

// iostream gives us std::cout, the console output.#include <iostream>// Every C++ program starts running in main().int main() {    std::cout << "Hello, world!" << std::endl;    // << chains several pieces into one line.    std::cout << "Welcome to " << "C++" << " in DMarlon Studio" << '\n';    // Numbers are printed just like text.    std::cout << "This course has " << 20 << " lessons." << '\n';    std::cout << "2 + 3 = " << 2 + 3 << '\n';    // \n starts a new line inside the text; \t inserts a tab.    std::cout << "Line one\nLine two\n";    std::cout << "Name:\tAda\n";    // Returning 0 tells the system that everything went well.    return 0;}

Output · c++ -std=c++17 main.cpp -o main && ./main

Hello, world!
Welcome to C++ in DMarlon Studio
This course has 20 lessons.
2 + 3 = 5
Line one
Line two
Name:	Ada

Key points

A program starts in int main() { ... }.
#include <iostream> gives you std::cout.
<< chains text and numbers into the output.
'\n' or std::endl start a new line.
Every statement ends with ;.

Exercise

Add three lines that print your name, your city and the result of 365 * 24 (the hours in a year), with a \t between each label and its value.