Blockchain use cases beyond crypto - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple blockchain block structure with a timestamp.

Blockchain / Solidity

block = {
    'timestamp': [1],
    'data': 'Sample data'
}

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

Atime.time()

Bdatetime.now()

Crandom.randint(1, 100)

D'2024-01-01'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a fixed string instead of a dynamic timestamp.

Using a random number instead of a timestamp.

The datetime.now() function provides the current timestamp for the block.

2fill in blank

medium

Complete the code to calculate the hash of a block's data using SHA-256.

Blockchain / Solidity

import hashlib

block_data = 'Transaction data'
hash_result = hashlib.[1](block_data.encode()).hexdigest()

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

Amd5

Bsha512

Csha1

Dsha256

Attempts:

3 left

💡 Hint

Common Mistakes

Using weaker hash functions like MD5 or SHA1.

Using a hash function not supported by hashlib.

The sha256 function from hashlib is used to create a secure hash for blockchain data.

3fill in blank

hard

Fix the error in the code to add a new transaction to the blockchain list.

Blockchain / Solidity

blockchain = []
new_transaction = {'sender': 'Alice', 'receiver': 'Bob', 'amount': 50}
blockchain.[1](new_transaction)

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

Aappend

Badd

Cextend

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using add which is for sets.

Using extend which expects an iterable.

The append method adds a single item to the end of a list, which is correct for adding a transaction.

4fill in blank

hard

Fill both blanks to filter transactions with amount greater than 100 and create a dictionary with sender as key.

Blockchain / Solidity

filtered = {tx['sender']: tx for tx in transactions if tx['amount'] [1] 100 and tx['receiver'] [2] 'Unknown'}

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

A>

B<

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than instead of greater than.

Using equality instead of inequality for receiver check.

The code filters transactions where amount is greater than 100 and receiver is not 'Unknown'.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps block IDs to their data if the block is verified.

Blockchain / Solidity

verified_blocks = {block[1]: block[2] for block in blocks if block[3] == True}

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

A['id']

B['data']

C['verified']

D['timestamp']

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong keys for dictionary mapping.

Checking the wrong field for verification.

The dictionary comprehension maps each block's ID to its data only if the block is verified.

Practice

1. Which of the following is a common use of blockchain technology beyond cryptocurrency?

easy

A. Creating new digital currencies only

B. Running traditional centralized databases

C. Tracking the origin and movement of goods in supply chains

D. Replacing all internet servers

Solution

1. Step 1: Understand blockchain beyond money

   Blockchain is used to keep safe and clear records, not just for digital money.

2. Step 2: Identify common non-crypto uses

   Tracking goods in supply chains is a popular use case to ensure transparency and trust.

3. Final Answer:

   Tracking the origin and movement of goods in supply chains -> Option C

4. Quick Check:

   Blockchain use beyond crypto = Tracking goods [OK]

Hint: Think of blockchain as a secure record keeper beyond money [OK]

Common Mistakes:

• Thinking blockchain only creates cryptocurrencies
• Confusing blockchain with regular databases
• Assuming blockchain replaces all internet servers

2. Which syntax correctly describes a smart contract in blockchain?

easy

A. contract SmartContract { function run() public {} }

B. smart contract run() {}

C. contract = SmartContract()

D. function smartContract run()

Solution

1. Step 1: Recognize smart contract syntax

   Smart contracts are written like small programs with a contract keyword and functions.

2. Step 2: Check syntax correctness

   contract SmartContract { function run() public {} } uses correct syntax with 'contract' keyword and function declaration.

3. Final Answer:

   contract SmartContract { function run() public {} } -> Option A

4. Quick Check:

   Correct smart contract syntax = contract SmartContract { function run() public {} } [OK]

Hint: Look for 'contract' keyword and function inside braces [OK]

Common Mistakes:

• Missing 'contract' keyword
• Using assignment instead of declaration
• Incorrect function declaration syntax

3. What will be the output of this simplified blockchain smart contract code snippet?

mapping(address => uint) public votes;
function vote() public {
  votes[msg.sender] += 1;
}
vote() called twice by same address.

medium

A. votes[msg.sender] = 1

B. votes[msg.sender] = 2

C. votes[msg.sender] = 0

D. Error: duplicate voting not allowed

Solution

1. Step 1: Understand the vote function

   Each call to vote() increases the caller's vote count by 1 in the votes mapping.

2. Step 2: Calculate votes after two calls

   Calling vote() twice adds 1 twice, so votes[msg.sender] becomes 2.

3. Final Answer:

   votes[msg.sender] = 2 -> Option B

4. Quick Check:

   Two votes increment count to 2 [OK]

Hint: Each call adds 1, so two calls add up to 2 [OK]

Common Mistakes:

• Assuming only one vote allowed
• Thinking votes reset after each call
• Confusing mapping with array

4. Identify the error in this blockchain voting smart contract snippet:

mapping(address => bool) public voted;
function vote() public {
  require(!voted[msg.sender]);
  voted[msg.sender] = true;
  votes += 1;
}

medium

A. votes variable is not declared

B. require statement syntax is wrong

C. voted mapping should be uint not bool

D. Function vote() missing return type

Solution

1. Step 1: Check variable declarations

   The code uses 'votes += 1' but 'votes' is not declared anywhere.

2. Step 2: Verify other parts

   require syntax and voted mapping type are correct; vote() functions in Solidity do not need return type.

3. Final Answer:

   votes variable is not declared -> Option A

4. Quick Check:

   Undeclared variable 'votes' causes error [OK]

Hint: Check if all variables used are declared [OK]

Common Mistakes:

• Assuming require syntax is wrong
• Thinking bool mapping is incorrect
• Expecting return type in void functions

5. You want to build a blockchain system to manage digital rights for music tracks. Which feature is most important to include beyond basic blockchain storage?

hard

A. Anonymous voting for favorite tracks

B. A cryptocurrency token for trading music

C. A centralized database for faster queries

D. Smart contracts to automate royalty payments

Solution

1. Step 1: Understand digital rights management needs

   Managing rights requires automatic, trustworthy payment distribution to artists.

2. Step 2: Identify blockchain feature for automation

   Smart contracts can run code to automate royalty payments when music is used or sold.

3. Step 3: Evaluate other options

   Cryptocurrency tokens and voting are unrelated; centralized database loses blockchain benefits.

4. Final Answer:

   Smart contracts to automate royalty payments -> Option D

5. Quick Check:

   Automate payments with smart contracts [OK]

Hint: Use smart contracts to automate rules and payments [OK]

Common Mistakes:

• Choosing cryptocurrency token instead of automation
• Using centralized database losing blockchain trust
• Confusing voting with rights management