01 · Setup & First Program

🎥 Video walkthrough

Install a C++ compiler

C++ source files are compiled directly to native machine code — there's no virtual machine in between. You need a compiler that implements at least C++17. Pick one for your platform:

# macOS -- Xcode command line tools (provides clang++)
xcode-select --install

# Ubuntu/Debian -- GCC
sudo apt install build-essential

# Windows -- either install MSYS2/MinGW-w64 (g++), or Visual Studio
# Community Edition (includes MSVC's cl.exe and a full IDE)

Verify the install:

g++ --version
# g++ (Homebrew GCC ...) 13.x   -- or similar

clang++ --version
# Apple clang version 15.x      -- macOS default

Either g++ or clang++ works fine for everything in this course; examples use g++ but the commands are interchangeable.

Compiling and running by hand

Create hello.cpp:

// hello.cpp
#include <iostream>

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

Compile, then run:

g++ -std=c++17 -Wall -o hello hello.cpp
# produces an executable named "hello"

./hello
# Hello, world!

• -std=c++17 tells the compiler which language standard to target. Always set this explicitly — the default varies by compiler and version.
• -Wall turns on common warnings. Treat warnings as bugs waiting to happen; get comfortable reading and fixing them from day one.
• -o hello names the output binary; without it you'd get a.out.

Anatomy of the program

Piece	Meaning
#include <iostream>	Pulls in the standard I/O library so std::cout is available.
int main()	The program's entry point — execution always starts here.
std::cout << ...	Streams text to standard output. std:: means "from the standard library's namespace."
std::endl	Inserts a newline and flushes the output buffer.
return 0;	Tells the operating system the program exited successfully (non-zero means an error occurred).
;	Every statement ends with a semicolon.
{ }	Curly braces delimit blocks — function bodies, loop bodies, class bodies.

Header files and translation units

Every #include textually pastes in the contents of another file before compilation. <iostream> is a standard library header — angle brackets < > tell the compiler to look in its standard include paths. Later, when you write your own headers, you'll use quotes instead: #include "myheader.h". Each .cpp file the compiler processes on its own is called a translation unit; multi-file programs are covered starting in Module 10.

Namespaces and using namespace std;

You'll often see using namespace std; at the top of beginner code so you can write cout instead of std::cout. It saves typing, but it also pulls everything from std into scope, which can cause silent name clashes in larger programs. This course spells out std:: explicitly — it's slightly more typing but it's what production C++ code does, and it makes clear exactly where every name comes from.

Choosing an editor

Any of these work well for this course: VS Code with the "C/C++" and "CMake Tools" extensions (free, lightweight, great for following along), CLion (excellent C++-specific tooling, paid but free for students), or your platform's default (Xcode on macOS, Visual Studio on Windows). VS Code is the most common lightweight choice — pick one and move on, since the editor matters far less than practice.

How It Actually Works

When you run g++/clang++ on a .cpp file, four distinct programs run in sequence, not one:

1. Preprocessor — textually expands #include (literally pastes the header's contents in), macros, and #ifdef blocks. The output is one huge "translation unit" of pure C++ with no directives left.
2. Compiler proper — parses that translation unit, type-checks it, and lowers it to assembly for your target CPU (x86-64, ARM64, ...). This is where int main() becomes real machine instructions — a prologue that reserves stack space, instructions for each statement, an epilogue that restores the stack and returns.
3. Assembler — turns the assembly text into an object file (.o), raw machine code plus a symbol table (a list of names like main and where they live in the file, so other tools can find them).
4. Linker — combines your object file(s) with the C++ standard library's already-compiled object code (iostream's internals aren't recompiled — they're pre-built), resolves every symbol reference to a final address, and produces one executable.

This is why a syntax error is a compiler error but calling an undefined function is a linker error ("undefined reference") — the compiler is happy to emit a call to a symbol it hasn't seen the body of yet; only the linker notices nothing defines it. It's also why C++ compiles to native code with no runtime interpreter: the executable you get is CPU instructions the OS loads directly, which is why C++ programs start instantly and why a binary built for macOS/ARM64 won't run on Linux/x86 — there's no portable bytecode layer like a JVM or CLR sits underneath.

🔀 See this in another language

• C# — What Is C# & .NET?
• Kotlin — Setup & First Program
• Shell/Bash — Setup & First Script

Exercise

Write a program greeter.cpp with a main function that prints a greeting for three different names, one per line, using std::cout. Compile it with g++ -std=c++17 -Wall -o greeter greeter.cpp and run the resulting binary from the command line.