Hello, World

Before writing any C++ code, you need a compiler — a program that translates your source files into machine code that the operating system can run.

Installing a compiler

# macOS — Xcode Command Line Tools ships clang++
xcode-select --install

# Ubuntu / Debian
sudo apt install g++ build-essential

# Fedora / RHEL
sudo dnf install gcc-c++

# Windows — install MinGW-w64 from mingw-w64.org, or use WSL

Verify the installation:

g++ --version
# or
clang++ --version

The program

Create a file named hello.cpp:

#include <iostream>

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

Explanation

#include <iostream> — A preprocessor directive that copies in the standard input/output stream library. Without it, std::cout does not exist. Angle brackets mean the header comes from the standard library; quotes ("myfile.h") mean it is a local file.

int main() — The entry point. The OS calls main when your program starts. int is the return type — an integer status code sent back to the shell.

std::cout — The standard character output stream. std is the standard namespace; :: is the scope resolution operator.

<< — The stream insertion operator. It sends the right-hand value into the stream on the left. Multiple << calls can be chained on one line.

std::endl — Inserts a newline and flushes the output buffer. "\n" inserts a newline without flushing and is faster in tight loops.

return 0; — Returns 0 to the shell, the conventional signal for success. Non-zero means error.

Compiling and running

g++ -std=c++17 hello.cpp -o hello
./hello

Output:

Hello, World!

-std=c++17 enables C++17 features. -o hello names the output binary; without it the compiler produces a.out.

Useful compiler flags

# Enable most warnings — use these on every project
g++ -std=c++17 -Wall -Wextra hello.cpp -o hello

# Optimized release build
g++ -std=c++17 -O2 hello.cpp -o hello

# Debug build with memory error detection
g++ -std=c++17 -g -fsanitize=address,undefined hello.cpp -o hello

-Wall -Wextra catch a large class of bugs at compile time. -fsanitize=address,undefined instruments the binary to detect memory errors and undefined behavior at runtime — run your test suite with this on during development.