Free CS curriculum · Free forever

Learn to code for a software engineering role.

Read a free computer-science curriculum here, then practice in the free Hack University app on your own computer: run the code, check your answers, and work in real projects.

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hackuniversity.dev/dashboard/learn/intro-to-computer-science/1-2

1/27 lessons4%

1. What a Program Is

✓Computers follow instructions

✓Run your first line of Python

✓Programs take input

✓Read the error, fix the bug

Lesson 1-2 · 10 min

Run your first line of Python

This is a whole program. One line, and it produces one line of output.

1print("Hello, world!")

Output

Hello, world!

Lesson 1-3 · 10 min

Programs take input

Change the input and the output changes with it. The instructions stayed identical.

1print("You typed:", input())

Output

You typed: hi there

Mark lesson complete✓ Completed

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Learn

A free coding curriculum for beginners and self-taught programmers.

If you are asking how to learn to code, start with a computer-science path that explains every idea in plain English, taking you from your first program to writing real software with confidence.

Every lesson is a walkthrough you read: worked examples, diagrams, and the reasoning behind each step. No account, no sign-up, and your place is remembered in your browser as you go.

Reading gets you started, and writing code makes it stick. The free app has lessons with practice problems it checks for you, so do both.

Browse the curriculum

hackuniversity.dev/dashboard/learn/intro-to-computer-science/1-2

1/27 lessons4%

1. What a Program Is

✓Computers follow instructions

✓Run your first line of Python

✓Programs take input

✓Read the error, fix the bug

Lesson 1-2 · 10 min

Run your first line of Python

This is a whole program. One line, and it produces one line of output.

1print("Hello, world!")

Output

Hello, world!

Lesson 1-3 · 10 min

Programs take input

Change the input and the output changes with it. The instructions stayed identical.

1print("You typed:", input())

Output

You typed: hi there

Mark lesson complete✓ Completed

← PrevOutlineNext →

Reference

Quick references for the tools you will actually use at work.

Sixty-five cheatsheets across languages, web, backend, networking, graphics, data, cloud, devops, testing, and tooling. Each one is a reference, not a tutorial, so you can find the exact syntax fast.

Sections are anchored and linkable, every code block has a copy button, and the whole library is open to everyone with no limits. In the free app, the cheatsheet sits beside the editor and you can run its examples on your computer.

Open the cheatsheets

hackuniversity.dev/cheatsheets/python/strings

On this page

Indexing and Slicing
String Formatting
Searching
Splitting and Joining

Indexing and Slicing

Take part of a string by index range. Both ends are optional and a negative index counts from the right.

1s = "Hello, World!"

2s[7:12] # 'World'

3s[::-1] # '!dlroW ,olleH'

String Formatting

f-strings, with the result written out beside each call.

CopyCopied

1name, age = "Alice", 30

2f"Name: {name}, Age: {age}"

3f"{3.14159:.2f}" # "3.14"

PracticeFree download

Run real code and real projects on your own computer.

The website is for reading. The free Hack University app is where you practice. It runs on your computer, so your code, your projects, and your databases stay with you.

Compilers for Python, JavaScript, TypeScript, C++, Java, Go, SQL, and Bash, with lessons, cheatsheets, and challenges that check your answers.
Courses for HTML, CSS, and JavaScript, React, Next.js, Express, FastAPI, Spring Boot, and Go APIs, each built around real codebases.
A project editor with a file explorer, terminals, servers on free ports, and PostgreSQL and MongoDB. Change any file, reset it, or keep your work.

localhost:3000/express/playground/stagepass-api

Explorer

src

modules

events

events.controller.ts

events.service.ts

events.repository.ts

app.ts

server.ts

requests.http

package.json

events.controller.tsport 23002▶ Run

1export async function listEvents(req, res) {

2 const events = await service.list(req.query);

3 res.json(events);

Terminal

$ npm run dev

StagePass API listening on port 23002

$ curl localhost:23002/v1/events

[{"id":1,"name":"Jazz Night"},{"id":2,"name":"Open Mic"}]

How you will use it:

Open a lesson, like Python loops, run its examples, then solve the practice and press Check until every test passes.
Try an idea in a compiler. Give a TypeScript function the wrong type and the type checker catches it before the code runs.
Open a real codebase, like the StagePass ticketing API, press Run, and call it from the API panel or the terminal.
Break things on purpose. Reset any file to the original, or keep your changes and come back later.

You need Node.js 24.12 or newer and Docker Desktop. Clone it and run one command:

git clone https://github.com/Valx01P/hack-university-compiler.git
cd hack-university-compiler
npm run up

Get the app on GitHub Star it on GitHub

If the app helps you, give it a star on GitHub. Stars help other students find it, and they tell us what to build next.

localhost:3000/python/learn/user-input/1

main.pyPrice with tax▶ RunCheck

1TAX_MULTIPLIER = 1.08

3item = input().strip()

4price = float(input())

5total = price * TAX_MULTIPLIER

6print(f"Item: {item}")

7print(f"With tax: {total:.2f}")

OutputResultsRun tries your code. Check runs it against 3 tests.

Press ▶ Run to execute your code. Output appears here.

Checking your code against 3 tests…

Solved! All 3 tests passed.

Next: A line of values →

Test 1 passed

Test 2 passed

Test 3 passed

Start working towards a software engineering role.

Read the whole curriculum and every cheatsheet, free and unlimited, with nothing to sign up for. Then practice it all in the free app on your own computer.

Start exploring Get the free app

Found it useful? Give it a star on GitHub