First smart contract deployment in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a smart contract named MyContract.

Blockchain / Solidity

contract [1] {
    // contract code
}

Drag options to blanks, or click blank then click option'

AMyContract

Bmycontract

CContract1

DSmartContract

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for the contract.

Using generic names like Contract1.

The contract name should start with a capital letter and match the deployment name. Here, MyContract is the correct name.

2fill in blank

medium

Complete the code to define a public state variable named owner of type address.

Blockchain / Solidity

address public [1];

Drag options to blanks, or click blank then click option'

Aowner

Bcreator

Cuser

Dadmin

Attempts:

3 left

💡 Hint

Common Mistakes

Using generic names like admin or user instead of owner.

Forgetting to declare the variable as public.

The variable owner is commonly used to store the address of the contract owner and is declared as public to allow external access.

3fill in blank

hard

Fix the error in the constructor to set the owner to the address that deploys the contract.

Blockchain / Solidity

constructor() {
    [1] = msg.sender;
}

Drag options to blanks, or click blank then click option'

Aaddress owner

Bowner

Cowner()

Dmsg.sender

Attempts:

3 left

💡 Hint

Common Mistakes

Using owner() which looks like a function call.

Trying to redeclare the variable inside the constructor.

The constructor should assign msg.sender to the state variable owner. Using owner directly is correct.

4fill in blank

hard

Fill both blanks to create a function named getOwner that returns the owner address.

Blockchain / Solidity

function [1]() public view returns ([2]) {
    return owner;
}

Drag options to blanks, or click blank then click option'

AgetOwner

Baddress

Cowner

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect return types like string.

Naming the function something unrelated.

The function name should be getOwner and it returns an address type.

5fill in blank

hard

Fill all three blanks to deploy the contract and assign the owner correctly.

Blockchain / Solidity

contract [1] {
    address public [2];
    constructor() {
        [3] = msg.sender;
    }
}

Drag options to blanks, or click blank then click option'

AMyContract

Bowner

Cadmin

Dcreator

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the owner variable in different places.

Forgetting to assign the owner in the constructor.

The contract name is MyContract, the state variable is owner, and the constructor assigns msg.sender to owner.

Practice

1. What does deploying a smart contract mean in blockchain?

easy

A. Testing the contract on a local computer only

B. Making the contract code live and usable on the blockchain

C. Writing the contract code in a text editor

D. Deleting the contract from the blockchain

Solution

1. Step 1: Understand deployment meaning

   Deployment means putting the contract code on the blockchain so it can run.

2. Step 2: Differentiate from writing and testing

   Writing is coding, testing is checking locally or on test networks, deployment is live on blockchain.

3. Final Answer:

   Making the contract code live and usable on the blockchain -> Option B

4. Quick Check:

   Deploy = live on blockchain [OK]

Hint: Deployment means contract is live on blockchain [OK]

Common Mistakes:

• Confusing deployment with just writing code
• Thinking testing is deployment
• Believing deployment deletes contracts

2. Which of the following is the correct Solidity syntax to start a simple contract named MyContract?

easy

A. contract MyContract { }

B. class MyContract { }

C. function MyContract() { }

D. contract = MyContract()

Solution

1. Step 1: Recall Solidity contract declaration

   Solidity uses the keyword contract followed by the contract name and braces.

2. Step 2: Check each option's syntax

   contract MyContract { } matches Solidity syntax; others use wrong keywords or formats.

3. Final Answer:

   contract MyContract { } -> Option A

4. Quick Check:

   Solidity contract starts with 'contract' keyword [OK]

Hint: Solidity contracts start with 'contract' keyword [OK]

Common Mistakes:

• Using 'class' instead of 'contract'
• Writing function instead of contract
• Assigning contract like a variable

3. Given this Solidity contract snippet deployed on a test network:

contract Counter {
  uint count = 0;
  function increment() public {
    count += 1;
  }
  function getCount() public view returns (uint) {
    return count;
  }
}

If you call increment() twice and then getCount(), what is the output?

medium

A. 0

B. 1

C. 2

D. Error: function not found

Solution

1. Step 1: Understand contract state changes

   Each call to increment() adds 1 to count, starting from 0.

2. Step 2: Calculate after two increments

   After two calls, count becomes 2. getCount() returns this value.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   2 increments = count 2 [OK]

Hint: Each increment adds 1; two increments mean count is 2 [OK]

Common Mistakes:

• Forgetting state changes persist on blockchain
• Assuming count resets each call
• Confusing function names

4. You try to deploy this Solidity contract but get a syntax error:

contract Simple {
  uint number
  function setNumber(uint num) public {
    number = num;
  }
}

What is the cause of the error?

medium

A. Missing return type in function

B. Function setNumber must be private

C. Contract name must be lowercase

D. Missing semicolon after uint number

Solution

1. Step 1: Check Solidity syntax rules

   Variable declarations require a semicolon at the end.

2. Step 2: Identify missing semicolon

   uint number line misses a semicolon, causing syntax error.

3. Final Answer:

   Missing semicolon after uint number -> Option D

4. Quick Check:

   Missing semicolon = syntax error [OK]

Hint: Check semicolons after variable declarations [OK]

Common Mistakes:

• Thinking function visibility causes syntax error
• Believing contract names must be lowercase
• Expecting return type for void functions

5. You want to deploy a smart contract that stores user names and their balances. Which approach is best to deploy and test it safely before using real money?

hard

A. Deploy on a test network like Ropsten or Goerli first

B. Deploy directly on the main Ethereum network

C. Write the contract but never deploy it

D. Deploy on a private computer without blockchain

Solution

1. Step 1: Understand deployment environments

   Mainnet uses real money; testnets simulate blockchain without real cost.

2. Step 2: Choose safe testing method

   Deploying on testnets like Ropsten or Goerli lets you test without risking real funds.

3. Final Answer:

   Deploy on a test network like Ropsten or Goerli first -> Option A

4. Quick Check:

   Testnet deployment = safe testing [OK]

Hint: Use test networks to avoid losing real money [OK]

Common Mistakes:

• Deploying directly on mainnet without testing
• Not deploying at all and missing testing
• Using private computer without blockchain for deployment