Worked examples

A program. The output. Then why.

Worked examples — a program, the output, then why. Chapter tutorials live under Courses. Python if you are new. C++, JavaScript, or Java if you already write code.

Run the first Python program All languages →

python · first program

Run

1 # The classic first Python program
2 print("Hello, World!")

Output

Hello, World!

Next · Add Two NumbersOpen →

Pick a language

Each card is a real first program. Open it, or browse the topic list.

544 worked examples

Start here if you are new

Python

7 topics · 165

Print, lists, files — then the rest of the language.

Print "Hello, World!"Run this →

1  # first program
2  print("Hello, World!")

Hello, World!

All Python topics →

If you already write code

C++

19 topics · 165

From Hello World through STL-sized problems.

Hello WorldRun this →

1  #include <iostream>
2  int main() { cout << "Hello World"; }

Hello World

All C++ topics →

The language of the browser

JavaScript

14 topics · 124

console.log, then the programs you actually ship.

Hello WorldRun this →

1  console.log("Hello World")

Hello World

All JavaScript topics →

Classes, then collections

Java

4 topics · 90

A main method, then the problems they solve.

Hello WorldRun this →

1  System.out.println("Hello, World!");

Hello, World!

All Java topics →

If syntax is not the hard partLogic buildingConditionals, loops, recursion, arrays, strings — six phases of problems, not a language tour.Open →