Your First C++ Program: Hello World Explained Line by Line

Every programmer's first program prints a message. In C++ that is five short lines, and each one teaches you something important.

The program#

Save this as hello.cpp:

#include <iostream>

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

Compile it and run it:

g++ -std=c++20 -Wall -Wextra hello.cpp -o hello
./hello

Hello, World!

Line by line#

Line 1: #include <iostream> brings in the standard library's input/output tools. Lines starting with # are instructions to the preprocessor, which runs before the compiler. iostream stands for "input/output stream", and it gives us std::cout.

Line 3: int main() defines the function where every C++ program starts. int means the function returns a whole number to the operating system when it finishes. The curly braces { and } mark the start and end of the function's body.

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

• std::cout ("character output") is the standard output, normally your terminal.
• << sends the value on its right into the stream on its left.
• "Hello, World!\n" is a string literal. \n is the newline character, which moves to the next line.
• The semicolon ; ends the statement. Forgetting it is the most common beginner error.
• std:: means "from the standard library's namespace". You will learn more in Syntax.

Line 5: return 0; ends main and tells the operating system the program succeeded. A non-zero value means an error. In main only, you may leave this line out and C++ returns 0 automatically.

Printing several things#

You can chain << to print several values in one statement, including numbers:

#include <iostream>

int main() {
    std::cout << "C++ was created in " << 1979 << ".\n";
    std::cout << "2 + 3 = " << 2 + 3 << '\n';
    std::cout << "One line, ";
    std::cout << "same line.\n";
}

C++ was created in 1979.
2 + 3 = 5
One line, same line.

Notice that std::cout does not add a newline by itself. Text keeps going on the same line until you print \n. A single character such as '\n' can be written in single quotes.

\n or std::endl?#

You will often see std::endl in other tutorials:

#include <iostream>

int main() {
    std::cout << "Line one" << std::endl;
    std::cout << "Line two\n";
}

Line one
Line two

Both end the line. std::endl also flushes the output (forces it to be written immediately), which is slower when printing many lines. Prefer '\n', and use std::endl only when you need the output to appear right away.

Escape sequences#

A backslash inside a string starts an escape sequence:

#include <iostream>

int main() {
    std::cout << "Name:\tAsha\n";
    std::cout << "She said \"hi\".\n";
    std::cout << "Path: C:\\Users\\asha\n";
}

Name:	Asha
She said "hi".
Path: C:\Users\asha

Reading compiler errors#

If you make a mistake, the compiler stops and tells you where. For example, without the semicolon:

#include <iostream>

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

g++ reports something like:

hello.cpp: In function 'int main()':
hello.cpp:4:35: error: expected ';' before '}' token

The message gives the file, line and column (4:35), and what it expected. Always fix the first error first; later errors are often caused by it.

Common mistakes#

Practice#

Name:	Asha
City:	Pune
Year:	2026

#include <iostream>

int main() {
    std::cout << "Name:\tAsha\n";
    std::cout << "City:\tPune\n";
    std::cout << "Year:\t" << 2026 << '\n';
}

Name:	Asha
City:	Pune
Year:	2026

Key takeaway#