StarkNet Cairo 101

Get started with Cairo with this simple tutorial. Complete the puzzles, get points and learn about StarkNet smart contracts!

Introduction

Disclaimer

Don’t expect any kind of benefit from using this, other than learning a bunch of cool stuff about StarNet, the first general purpose validity rollup on the Ethereum Mainnnet.

StarkNet is still in Alpha. This means that develpment is ongoing, and the paint is not dry everywhere. Things will get better, and in the meanwhile, we make things work with a bit of duct tape here and there!

How it works

This workshop is a set of smart contracts deployed on StarkNet Alpha on testnet. Each smart contract is an exercice/puzzle; each one outlines a feature of the Cairo Smart contract language. Completing the exercice will credit you with points, in the form of an ERC20 token.

This workshop focuses on reading Cairo code and StarkNet smart contracts, in order to understand its syntax. You don’t need to code or install anything on your machine in order to follow and complete it. Getting started (doing the first two exercises) will take you some time, in order to get into the tutorial. Hang on! Once there, things will flow more easily. You’re learning!

This workshop is the first in a serie that will cover broad smart contract concepts (writing and deploying ERC20/ERC721, bridging assets, L1 <-> L2 messaging…).
Interested in helping writing those? Reach out!

Providing feedback

Once you are done working on this tutorial, your feedback would be greatly appreciated! Please fill this form to let us know what we can do to make it better. And if you struggle to move forward, do let us know! This workshop is meant to be as accessible as possible; we want to know if it’s not the case.

Getting started

What will change soon

• As of 05/01/2021, transactions in StarkNet can still be done without an account contract. This tutorial currently leverages this possibility. Once account contracts become more widespread and usable, it will change to reflect that.
• Voyager struggles with hexadecimal / decimal conversion. For now, you should input all your value in voyager in the decimal format

Creating an account contract

In order to complete the tutorial you need to collect points. These points will be owned by a smart contract wallet, that you need to deploy.

• The easiest way to set one up is currently to use Argent X(download the chrome extension or check their repo.
• Follow the instructions to install the extension and deploy an account contract
• Make sure you are on the Goerli testnet network
• The tutorial’s points are held in contract 0x0555750f277a7abd2d7abf4c16806554bd750eb26d87ce58c6cb13b2158dcbc1. Click on “add token” in Argent X to get your points balance to show up there!

Using voyager

For this tutorial we’ll interact with our contracts through Voyager, StarkNet’s block explorer. When looking for a contract / transaction, always make sure you are on the Goerli version of Voyager!

• Access your transactions with URL https://goerli.voyager.online/tx/your-tx-hash
• Access a contract with URL https://goerli.voyager.online/contract/your-contract-address
• Access read/write functions of the contract with the “read/write contract” tab in voyager

Using decimals instead of hexadecimal

Voyager currently has issues dealing with hexadecimal values when writing values to contracts.

For example, reading your points balance through voyager currently does not work if you input your Argent X address as hexadecimal.

To overcome this limitation, always convert your hexadecimal value to decimal. I use this website.

Getting points

Each exercice is a separate smart contract. It contains code that, when executed properly, will distribute points to your address. Since there is no way currently to send a transaction easily through your account contract, you’ll have to specify your address for each call.

Points are distributed by the function distribute_points() while the function validate_exercice records that you completed the exercice (you can get points only once). Your goal is to:

• Read the code of the exercices in the current repo
• Find where the calls to distribute_points() are in the code
• Read the comments of the code to get further instructions if needed
• Manage to call the functions correctly through voyager to trigger it.

Checking your progress

Counting your points

Your points will get credited in Argent X; though this make take so time. If you want to monitor your points count in real time, you can also see your balance in voyager!

• Go to the ERC20 counter in voyager, in the “read contract” tab
• Enter your address in decimal in the “balanceOf” function

Transaction status

You sent a transaction, and it is shown as “undected” in voyager? This can mean two things:

• Your transaction is pending, and will be included in a block shortly. It will then be visible in voyager.
• Your transaction was invalid, and will NOT be included in a block (there is no such thing as a failed transaction in StarkNet).

You can (and should) check the status of your transaction with the following URL https://alpha4.starknet.io/feeder_gateway/get_transaction_receipt?transactionHash= , where you can append your transaction hash.

Contract addresses

Contributing

Help is welcome!

This project can be made better, and will evolve in the coming weeks. Your contributions are welcome! Here are things that you can do to help:

• Correct bugs if you find some
• Add explanation in the comments of the exercice if you feel it needs more explanation
• Add exercices showcasing your favorite Cairo feature

Reusing this project

This project uses Nile.

git clone https://github.com/l-henri/starknet-cairo-101
cd starknet-cairo-101
python3 -m venv env
source env/bin/activate
pip install cairo-nile
nile compile

GitHub

View Github