Hello, World!

There’s a tradition in the programming world: the first program you write in any new language should display “Hello, World!” on the screen. This tradition started with the legendary book “The C Programming Language” back in 1978. Now it’s your turn to carry on the tradition!

Your First Program

Here’s the Hello World program in C++:

#include <iostream>

int main() {
    std::cout << "Hello, World!" << std::endl;
    return 0;
}

Type this code in the playground, then click Run. You should see:

Hello, World!

Congratulations! You just wrote your first C++ program! It may look simple, but there’s a lot going on behind the scenes. Let’s break down every line.

Breaking Down Every Line

Line 1: #include <iostream>

#include <iostream>

This line is a preprocessor directive — an instruction telling the compiler to “include” a header file called iostream. This file contains definitions for cout (output to screen) and cin (input from keyboard).

Think of it this way: you want to cook, but your knife is in the drawer. #include is like opening the drawer and taking out the tool you need. Without #include <iostream>, you can’t use cout to display text.

Key facts:

• #include always starts with the hash symbol #
• <iostream> stands for “input/output stream” — a stream of data flowing in and out
• The header file name is enclosed in < and > (not quotes)
• This line does not end with a semicolon (;)

Line 3: int main() {

int main() {

This is the main function — the entry point of the program. Every C++ program must have a main() function. When you run the program, the computer looks for this function and starts executing the code inside it.

Think of your program as a building. main() is the front door — no matter how big the building is, everyone enters through the front door. Likewise, no matter how complex the code is, execution always starts from main().

Let’s break down its parts:

• int — the return type of the function (integer/whole number). main() returns a number to the operating system (0 means success)
• main — the function name. This name must be main, you can’t change it
• () — parentheses for parameters (empty means it takes no parameters)
• { — opening curly brace, marking the start of the function body

Line 4: std::cout << "Hello, World!" << std::endl;

    std::cout << "Hello, World!" << std::endl;

This is the line that does the actual work — displaying text on screen. There’s quite a lot happening here, so let’s break it down piece by piece:

std::cout — this is the “output stream” object. Think of cout like a megaphone — whatever you “send” to the megaphone gets heard (in this case, appears on screen). cout stands for “character output”.

<< — this is the insertion operator or “send to” operator. Think of it like an arrow: you’re sending something TO cout. The arrow << points to the left, toward cout.

"Hello, World!" — this is a string literal — text enclosed in double quotes. Whatever is inside the quotes will be displayed exactly as you wrote it.

<< std::endl — endl stands for “end line”. It adds a new line after the text, like pressing Enter. Without endl, the next text would appear on the same line.

; — the semicolon at the end of the line. In C++, every statement must end with a semicolon. It’s like a period at the end of a sentence — it tells the compiler that this instruction is complete.

Line 5: return 0;

    return 0;
}

return 0; tells the operating system that the program ran successfully. The number 0 is a universal convention for “everything went fine”. If the program returns a number other than 0, it means something went wrong.

Imagine you were sent to the store by a parent. When you come back, you say “Done, everything went smoothly!” — that’s the equivalent of return 0. If you say “There was a problem, the store was closed” — that’s like return 1.

} — the closing curly brace, marking the end of the main() function body.

Full Visualization

#include <iostream>     // 1. Get the tools we need (cout, endl)

int main() {            // 2. Entry point of the program
    std::cout << "Hello, World!" << std::endl;  // 3. Display text on screen
    return 0;           // 4. Report to OS: "Success!"
}                       // 5. End of program

Hello World Variations

Now try a few variations to solidify your understanding.

Displaying multiple lines:

#include <iostream>

int main() {
    std::cout << "Hello, World!" << std::endl;
    std::cout << "My name is Budi." << std::endl;
    std::cout << "I'm learning C++!" << std::endl;
    return 0;
}

Output:

Hello, World!
My name is Budi.
I'm learning C++!

Combining text in a single cout:

#include <iostream>

int main() {
    std::cout << "Hello" << " " << "World!" << std::endl;
    return 0;
}

You can use << multiple times to send several pieces of text to cout in a single statement.

Without std::endl (using \n):

#include <iostream>

int main() {
    std::cout << "First line\n";
    std::cout << "Second line\n";
    return 0;
}

\n is an escape character for a new line. It works similarly to std::endl, but is more concise. We’ll discuss the differences in more detail in the input/output lesson.

Common Mistakes

When writing your first program, there are some mistakes that come up frequently:

1. Forgetting the semicolon:

std::cout << "Hello" << std::endl  // ERROR: missing ';'

2. Misspelling cout:

std::cot << "Hello" << std::endl;  // ERROR: 'cot' is not 'cout'

3. Forgetting #include <iostream>:

int main() {
    std::cout << "Hello" << std::endl;  // ERROR: cout is not recognized
    return 0;
}

4. Using single quotes for strings:

std::cout << 'Hello' << std::endl;  // ERROR: single quotes are only for ONE character

Summary

You’ve successfully written and understood your first C++ program! In the next lesson, we’ll learn about comments — how to add notes inside your code — and understand the structure of a C++ program more deeply.