// This line allows us to use input and output (like printing on the screen)
#include <iostream>
using namespace std;

// main() function: this is where every C++ program starts running
int main() {
    // This line prints "Hello World" on the screen
    cout << "Hello World";

    // This line tells the computer that the program ended successfully
    return 0;
}

Hello World

Hello World Program in C++

This is the famous "Hello World" program in C++. It is usually the first program you write when you start learning C++.

The main purpose of this program is to show a simple message on the screen: ## Hello World.

Even though the program looks small, it contains many important concepts of C++ that you will use again and again.

What does this program do?

• It starts the C++ program.
• It uses the C++ library for input and output.
• It prints the text "Hello World" on the screen.
• It then ends the program properly.

1. Preprocessor Directive: #include <iostream>

#include <iostream>

• The word "include" means "add this file before compiling the program".
• "iostream" is a built-in C++ library.
• This library allows us to do input and output operations.
  • Input means taking data from the user.
  • Output means showing data on the screen.
• In this program, we use "cout", which is defined inside the iostream library.

Without this line, the computer does not know what "cout" is, and the program will not compile.

2. Header Files (simple idea)

• A header file is like a toolbox.
• Each header file has tools (functions, classes, etc.) that we can use in our program.
• When we write #include <iostream>, we are saying: "Please attach the toolbox that has input and output tools."

Examples:

• iostream → used for input and output (cout, cin)
• string → used to work with text (strings)
• math-related headers → used for mathematical functions

3. Namespace: using namespace std;

using namespace std;

• C++ stores many built-in names like cout, cin, string, etc., inside a group called "std".
• This group is called a "namespace".
• The line "using namespace std;" tells the compiler: "I want to use the names inside the std group directly."

Without this line, we would have to write "std::cout" instead of "cout".

So:

• With using namespace std; → we can write: cout << "Hello World";
• Without it → we must write: std::cout << "Hello World";

For beginners, using namespace std; makes the code easier to read and write.

4. Main Function: int main() { ... }

int main() { // code return 0; }

• Every C++ program must have a function named "main".
• The main function is the starting point of the program.
• When you run the program, the computer starts reading and executing code from inside main.

Let's break it:

• "int" before main means that this function returns an integer (a whole number).
• The round brackets () after main mean it is a function.
• The curly braces { and } mark the beginning and the end of the main function.
  • All the code that should run when the program starts is written between these braces.

In simple words: main() is the entry gate of your C++ program.

5. Comments in the Code

Examples in the code: // This line allows us to use input and output (like printing on the screen)

• A comment starts with // in C++.
• Anything written after // on that line is ignored by the compiler.
• Comments do not affect how the program runs.
• They are written only for humans to understand the code better.

Why are comments useful?

• They make the code easier to read.
• They explain what each part of the code is doing.
• They help beginners remember concepts.

Good habit: Write comments to describe your logic, especially when you are learning.

6. Output Statement: cout << "Hello World";

This is the most important line in this program:

cout << "Hello World";

• "cout" stands for "character output".
• The "<<" operator is used to send data to the output stream.
• "Hello World" is the text we want to display.

What happens:

1. The computer sees cout << "Hello World"
2. It sends the text "Hello World" to the output (usually the screen).
3. The text appears on your screen.

7. Return Statement: return 0;

return 0;

• This line tells the operating system that the program ended successfully.
• Returning 0 means "no errors occurred".
• Any non-zero value would indicate an error.

Why return 0?

• It's a convention in programming.
• 0 = success, non-zero = error
• The operating system can check this value to know if your program ran correctly.

Next Steps

After understanding this program, you can:

• Try modifying the message
• Add more output statements
• Learn about variables and data types
• Explore input operations with cin