In this C++ tutorial, you will learn how to write, understand, compile, and run a simple C++ Hello World program that prints Hello World! to standard output.

C++ Hello World Program

A Hello World program is a small C++ program used to verify that the basic source-code, compiler, and execution workflow is working. It also introduces the structure of a C++ program, including the main() function and console output with cout.

The following C++ program prints Hello World! to standard output.

main.cpp

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#include <iostream>  
using namespace std;

int main() {
   cout << "Hello World!";
}

The file is named main.cpp. The .cpp extension is commonly used for C++ source files.

Output of the C++ Hello World Program

When the program runs successfully, it writes the following text to standard output:

Hello World!

How the C++ Hello World Program Works

Let us examine each part of the program.

Line 1: #include <iostream>

The #include <iostream> directive makes declarations from the standard input/output stream library available to the program. In this example, it is needed for cout, which writes text to standard output.

C++ provides many standard headers for different features. A program can include additional headers when it needs the declarations provided by those headers. Programs can also include project-specific header files.

Line 2: using namespace std;

The standard C++ library places names such as cout inside the std namespace. The statement using namespace std; allows this example to write cout instead of std::cout.

For larger programs, explicitly qualifying standard-library names with std:: is often preferred because it makes their namespace clear and helps avoid name conflicts.

Line 3: This is an empty line. Blank lines and ordinary whitespace can be used to make source code easier to read. They do not change the behavior of this program.

Line 4: int main() {

This defines the main function. In a normal hosted C++ program, execution starts in the main() function. The return type int means that main() returns an integer status value to the execution environment. The opening brace { begins the function body.

Line 5: cout << "Hello World!";

cout is the standard output stream. The stream insertion operator << sends the string literal "Hello World!" to that stream. The semicolon ; terminates the statement.

Line 6: }

The closing brace } ends the body of the main() function. Because execution reaches the end of main() without an explicit return statement, C++ treats it as a successful return from main(), equivalent to returning zero.

C++ Hello World Using std::cout

The same program can be written without using namespace std;. In that case, qualify cout with its namespace and write std::cout.

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#include <iostream>

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

Both versions produce the same output. The difference is only in how the name cout is referenced.

Compile and Run the C++ Hello World Program

If a C++ compiler such as GCC is installed, save the source code as main.cpp and compile it from a terminal with g++.

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g++ main.cpp -o hello

On Linux or macOS, run the generated executable with:

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./hello

On Windows, when using a compiler that creates hello.exe, you can run the executable from the appropriate terminal with:

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hello.exe

The program should print Hello World!. You can also run the same source file through an IDE, VS Code configured with a C++ compiler, or an online C++ compiler.

Print Hello World with a New Line in C++

The original example prints the text without explicitly adding a line break. To move the output position to the next line, append \n to the string:

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#include <iostream>

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

You can also use std::endl:

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#include <iostream>

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

Both forms place subsequent output on a new line. std::endl additionally flushes the output stream, so a newline character such as \n is commonly sufficient when an immediate flush is not required.

Common C++ Hello World Compilation Mistakes

  • Missing #include <iostream>: std::cout is declared by the <iostream> header.
  • Using cout without its namespace: use std::cout, or keep the existing using namespace std; statement.
  • Missing semicolon: the output statement must end with ;.
  • Incorrect quotation marks: use normal double quotes around the string, such as "Hello World!".
  • Saving the source with the wrong extension: save C++ source code with a suitable extension such as .cpp.
  • No compiler configured: an editor such as VS Code edits the file, but a C++ compiler is still required to turn the source code into an executable program.

C++ Hello World Program Structure at a Glance

  • #include <iostream> provides the standard stream declarations used for console output.
  • main() is where execution begins for this program.
  • cout or std::cout writes data to standard output.
  • << inserts the text into the output stream.
  • "Hello World!" is a string literal.
  • The semicolon ends the output statement, and the braces delimit the body of main().