Your First C++ Program: Hello World

The classic first program prints a message on the screen.

#include <iostream>

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

Understand every line

Code	Meaning
#include <iostream>	Adds the input and output library, so we can use std::cout
int main()	The starting point. Every C++ program has one main
{ }	A block of code
std::cout	The standard output stream (the screen). std:: means it is in the std namespace
<<	The insertion operator: sends the text to the stream
std::endl	A new line, and it also flushes the output
return 0;	Tells the system that the program ended well. In main it is optional

Newline: \n or std::endl

#include <iostream>

int main() {
    std::cout << "First line\n";
    std::cout << "Second line" << std::endl;
    std::cout << "Tab:\tdone\n";
}

'\n' is faster. std::endl also flushes the buffer, which is slow if you do it many times.

The new way: std::print (C++23)

C++23 has std::print and std::println, which are easy and use the same format as std::format:

#include <print>

int main() {
    std::println("Hello, {}!", "World");
    std::println("{} + {} = {}", 2, 3, 2 + 3);
}

Your compiler must support it (GCC 14 or newer, recent Clang and MSVC).

What if there is a mistake?

#include <iostream>

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

Read the error from the top. It shows the file, the line and what is expected.

Common beginner mistakes

• A missing semicolon ; at the end of a statement.
• Forgetting #include <iostream>.
• Writing cout without std:: (or without using namespace std;).
• Using >> for output or << for input.

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