Starknet's Counter Workshop

In this workshop, you will learn how to create a simple Starknet smart contract, implement public functions, events, and access external contracts.

After completing each step, run the associated script to verify it has been implemented correctly.

Use the Cairo book and the Starknet docs as a reference.

Setup

1. Clone this repository
2. Create a new file called counter.cairo inside the src folder
3. Copy the following code into the file

#[starknet::contract]
mod Counter {
    #[storage]
    struct Storage {}
}

Note: You'll be working on the counter.cairo file to complete the requirements of each step. The file prev_solution.cairo will show up in future steps as a way to catch up with the workshop if you fall behind. Don't modify that file.

The next setup steps will depend on wether you prefer using Docker to manage global dependencies or not.

Option 1: Without Docker

4. Install Scarb 2.5.1 (instructions)
5. Install Starknet Foundry 0.16.0 (instructions)
6. Install the Cairo 1.0 extension for VSCode (marketplace)
7. Run the tests to verify the project is setup correctly

$ scarb test

Option 2: With Docker

4. Make sure Docker is installed and running
5. Install the Dev Containers extension for VSCode (marketplace)
6. Launch an instance of VSCode inside of the container by going to View -> Command Palette -> Dev Containers: Rebuild and Reopen in Container
7. Open VSCode's integrated terminal and run the tests to verify the project is setup correctly

$ scarb test

Note: All the commands shown from this point on will assume that you are using the integrated terminal of a VSCode instance running inside the container. If you want to run the tests on a different terminal you'll need to use the command docker compose run test.

Step 1

Checkout the step1 branch to enable the verification tests for this section.

$ git checkout -b step1 origin/step1

Goal

In this step, you will need to do the following:

1. Store a variable named counter as u32 type in the Storage struct.
2. Implement the constructor function that initializes the counter variable with a given input value.
3. Implement a public function named get_counter() which returns the value of the counter variable.

Requirements

• The get_counter() function must be within the contract's interface named ICounter.

Note: Any other given name to the contract's interface would break the test, be sure to have to correct name!

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• Storage variables are the most common way to interact with your contract storage. You can read more about it in Chapter 12.3.1 - Contract Storage.
• The constructor function is a special type of function that runs only once. You can read more about it in Chapter 12.3.2 - Constructor Function.
• To create a contract interface, you will need to define a trait with the name ICounter (otherwise the tests will fail) and mark the trait with the [starknet::interface] attribute. You can read more about it in Chapter 12.5 Interfaces.
• The get_counter() function should only be able to read the state of the contract and not modify it. You can read more about it in Chapter 12.3.2 - View functions.

Step 2

Checkout the step2 branch to enable the verification tests for this section.

$ git checkout -b step2 origin/step2

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Implement a function called increase_counter() that can increment the current value of the counter by 1 each time it is invoked.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• The increase_counter() function should be able to modify the state of the contract (also called an external function) and update the counter value within the Storage. You can read more about it in Chapter 12.3.2 - External Functions.

Step 3

Checkout the step3 branch to enable the verification tests for this section.

$ git checkout -b step3 origin/step3

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

In this step, you will need to do the following:

1. Import the KillSwitch contract interface into your project.
2. Store a variable named kill_switch as type IKillSwitchDispatcher in the Storage.
3. Update the constructor function to receive an additional input variable with the type ContractAddress.
4. Update the constructor function to initialize the kill_switch variable with the newly added input variable. Note that you need to use the IKillSwitchDispatcher which expects a ContractAddress as its type.

Note: Analyze the KillSwitch code to understand the interface and the contract structure from here. This is already added as a dependency in your Scarb.toml file.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• You need to import Dispatcher and DispatcherTrait of the KillSwitch contract. These dispatchers are automatically created and exported by the compiler. More information about Contract Dispatcher can be found in Chapter 12.5.2 - Contract Dispatcher.
• In the constructor, you can update the variable kill_switch with the IKillSwitchDispatcher { contract_address: ??? }, which expects the address of the external contract.

Note: If you want to deploy the Counter contract, you can use the following deployed KillSwitch contract address.

Goerli

Contract Address: 0x033b2c899fd8f89e3e1d5b69c4d495f1018a1dbb8c19b18795c2e16b078da34d

• Voyager
• Starkscan

Step 4

Checkout the step4 branch to enable the verification tests for this section.

$ git checkout -b step4 origin/step4

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Implement the KillSwitch mechanism in the increase_counter() by calling the is_active() function from the KillSwitch contract.

Requirements

• If the function is_active() from the KillSwitch contract returns true, then allow the increase_counter() to increment the value.
• If the function is_active() from the KillSwitch contract returns false, then return without incrementing the value.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• You can access the is_active() function from your kill_switch variable. Use this to create the logic in the increase_counter() function.

Step 5

Checkout the step5 branch to enable the verification tests for this section.

$ git checkout -b step5 origin/step5

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

In this step, you will need to do the following:

1. Implement an event named CounterIncreased which emits the current value of the counter.
2. Emit this event when the counter variable has been successfully incremented.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• Events are custom data structures that are emitted by a contract. More information about Events can be found in Chapter 12.3.3 - Contract Events.

Step 6 (Final)

Checkout the step6 branch to enable the verification tests for this section.

$ git checkout -b step6 origin/step6

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Check that you have correctly created an account contract for Starknet by running the full test suite:

$ scarb test

If the test suite passes, congratulations, you have created your first Counter Smart Contract on Starknet.