Development tools setup (Hardhat, Remix) in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Hardhat compile command

What is the expected output when you run npx hardhat compile in a new Hardhat project with a valid contracts/ folder containing Solidity files?

A Compilation finished successfully. Artifacts saved to the artifacts/ directory.

B Error: No Solidity files found in the contracts/ directory.

C Warning: No network configured. Compilation skipped.

D SyntaxError: Unexpected token in Hardhat config file.

💡 Hint

Think about what happens when you compile Solidity contracts with Hardhat.

When you run npx hardhat compile with valid Solidity files, Hardhat compiles them and saves the output artifacts. If no errors occur, it confirms successful compilation.

❓ Predict Output

intermediate

Remix IDE Solidity compilation result

In Remix IDE, after writing a valid Solidity contract and clicking the Compile button, what is the expected result shown in the Compile tab?

A Warning: Remix requires a Hardhat node to compile contracts.

B Error: Remix cannot connect to the Ethereum network.

C SyntaxError: Missing semicolon in Solidity code.

D Compilation successful with no errors or warnings.

💡 Hint

Remix compiles Solidity code directly in the browser.

Remix compiles Solidity contracts in-browser and shows success if code is valid. It does not require external nodes to compile.

🧠 Conceptual

advanced

Hardhat network configuration for local testing

Which Hardhat configuration snippet correctly sets up a local network named 'localhost' on port 8545 for testing?

A "networks": { "localhost": { "url": "http://127.0.0.1:8545" } }

B "networks": { "localhost": { "host": "127.0.0.1", "port": 8545 } }

C "networks": { "localhost": { "endpoint": "http://localhost:8545" } }

D "networks": { "localhost": { "address": "127.0.0.1:8545" } }

💡 Hint

Hardhat uses a URL string to specify network endpoints.

Hardhat network configuration requires a URL key with the full HTTP address including port. Other keys like host or port alone are invalid.

🔧 Debug

advanced

Identify the error in Hardhat config file

Given this Hardhat config snippet, what error will occur when running npx hardhat compile?

module.exports = {
  solidity: "0.8.18",
  networks: {
    localhost: {
      url: "http://127.0.0.1:8545",
    }
  },
  // missing comma here
  paths: {
    sources: "./contracts"
  }
};

A TypeError: Cannot read property 'url' of undefined

B SyntaxError: Unexpected token 'paths' - missing comma after networks object

C Error: Solidity version 0.8.18 not supported

D No error, compilation proceeds normally

💡 Hint

Check punctuation between object properties in JavaScript objects.

In JavaScript objects, properties must be separated by commas. Missing a comma causes a SyntaxError.

🚀 Application

expert

Deploying a contract using Hardhat script

Which script correctly deploys a Solidity contract named MyToken using Hardhat and logs the deployed address?

A

async function main() {
  const MyToken = await ethers.getContractFactory("MyToken");
  const token = MyToken.deploy();
  console.log(`Deployed to: ${token.address}`);
}

main().catch(console.error);

B

async function main() {
  const token = await ethers.deployContract("MyToken");
  console.log(`Deployed to: ${token.address}`);
}

main();

C

async function main() {
  const MyToken = await ethers.getContractFactory("MyToken");
  const token = await MyToken.deploy();
  await token.deployed();
  console.log(`Deployed to: ${token.address}`);
}

main().catch(console.error);

D

function main() {
  const MyToken = ethers.getContractFactory("MyToken");
  const token = MyToken.deploy();
  console.log(`Deployed to: ${token.address}`);
}

main();

💡 Hint

Remember to await deployment and the deployed promise before accessing the address.

The correct deployment script awaits the contract factory, deploys the contract, waits for deployment to finish, then logs the address. Missing awaits or async cause errors or undefined addresses.

Practice

1. Which of the following best describes Hardhat in blockchain development?

easy

A. A hardware device to store private keys securely

B. A local development environment to write and test smart contracts

C. An online marketplace for buying cryptocurrencies

D. A blockchain explorer to view transactions

Solution

1. Step 1: Understand Hardhat's purpose

   Hardhat is designed as a local tool to help developers write, test, and deploy smart contracts easily on their computer.

2. Step 2: Compare options with Hardhat's role

   Options A, B, and D describe other blockchain tools or devices, not Hardhat.

3. Final Answer:

   A local development environment to write and test smart contracts -> Option B

4. Quick Check:

   Hardhat = Local development tool [OK]

Hint: Hardhat runs locally for coding and testing smart contracts [OK]

Common Mistakes:

• Confusing Hardhat with hardware wallets
• Thinking Hardhat is an online platform
• Mixing Hardhat with blockchain explorers

2. Which command correctly initializes a new Hardhat project in your terminal?

easy

A. npx hardhat

B. npx hardhat init

C. hardhat start

D. hardhat create project

Solution

1. Step 1: Recall Hardhat initialization command

   The standard way to start a Hardhat project is by running npx hardhat which launches the setup wizard.

2. Step 2: Evaluate other options

   Options A, B, and C are not valid Hardhat commands for project initialization.

3. Final Answer:

   npx hardhat -> Option A

4. Quick Check:

   Initialize Hardhat with 'npx hardhat' [OK]

Hint: Use 'npx hardhat' to start a new project setup [OK]

Common Mistakes:

• Using 'hardhat create project' which is invalid
• Trying 'hardhat start' instead of 'npx hardhat'
• Using 'npx hardhat init' which is not a valid command

3. What will be the output when you run this Hardhat command in a new project folder?

npx hardhat compile

medium

A. Starts a local blockchain node

B. Throws an error: command not found

C. Deletes all compiled files

D. Compiles smart contracts and shows success message

Solution

1. Step 1: Understand the 'compile' command in Hardhat

   The command npx hardhat compile compiles all smart contracts in the project and outputs success or error messages.

2. Step 2: Check other options

   Throws an error: command not found is wrong because the command exists. Deletes all compiled files is incorrect as it does not delete files. Starts a local blockchain node is for running nodes, not compiling.

3. Final Answer:

   Compiles smart contracts and shows success message -> Option D

4. Quick Check:

   'npx hardhat compile' compiles contracts [OK]

Hint: Compile contracts with 'npx hardhat compile' to check code [OK]

Common Mistakes:

• Expecting 'compile' to start blockchain node
• Thinking 'compile' deletes files
• Assuming command is invalid without setup

4. You tried to deploy a contract using Hardhat but got this error:
Error: Cannot find module '@nomiclabs/hardhat-ethers'
What is the most likely fix?

medium

A. Install the missing plugin with npm install --save-dev @nomiclabs/hardhat-ethers

B. Restart your computer

C. Delete the node_modules folder without reinstalling

D. Run npx hardhat compile again

Solution

1. Step 1: Identify the missing module error

   The error says the plugin '@nomiclabs/hardhat-ethers' is missing, meaning it is not installed in the project.

2. Step 2: Fix by installing the missing plugin

   Running npm install --save-dev @nomiclabs/hardhat-ethers adds the plugin so Hardhat can use it.

3. Final Answer:

   Install the missing plugin with npm install --save-dev @nomiclabs/hardhat-ethers -> Option A

4. Quick Check:

   Missing module error = install plugin [OK]

Hint: Install missing packages with npm to fix module errors [OK]

Common Mistakes:

• Restarting computer without installing packages
• Deleting node_modules without reinstalling
• Running compile without fixing dependencies

5. You want to quickly test a simple smart contract without installing anything locally. Which tool should you use and why?

hard

A. Use Hardhat because it runs in the browser without installation

B. Use a hardware wallet to write contracts securely

C. Use Remix because it is an online editor that requires no local setup

D. Use a blockchain explorer to deploy contracts

Solution

1. Step 1: Identify tools for quick testing without local setup

   Remix is an online IDE that lets you write, compile, and deploy contracts directly in the browser.

2. Step 2: Compare with other options

   Hardhat requires local installation, hardware wallets store keys but don't write contracts, and blockchain explorers only view data.

3. Final Answer:

   Use Remix because it is an online editor that requires no local setup -> Option C

4. Quick Check:

   Quick test without install = Remix online editor [OK]

Hint: Remix runs in browser, no install needed for quick tests [OK]

Common Mistakes:

• Thinking Hardhat runs in browser without install
• Confusing hardware wallets with development tools
• Trying to deploy contracts via blockchain explorers