Multi-signature wallet concept in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this multi-signature wallet approval count?

Consider a multi-signature wallet contract where 3 owners must approve a transaction. The code below simulates approvals. What is the final approval count?

Blockchain / Solidity

approvals = {'owner1': True, 'owner2': False, 'owner3': True}
approval_count = sum(1 for approved in approvals.values() if approved)
print(approval_count)

A 1

B 2

C 3

D 0

💡 Hint

Count how many owners have True as their approval status.

Only 'owner1' and 'owner3' have approved (True), so the count is 2.

🧠 Conceptual

intermediate

Which statement best describes a multi-signature wallet?

Choose the correct description of a multi-signature wallet.

A A wallet that automatically sends funds to multiple recipients.

B A wallet that stores multiple cryptocurrencies in one address.

C A wallet that can only be accessed by one owner at a time.

D A wallet that requires multiple private keys to authorize a transaction.

💡 Hint

Think about how multiple people approve spending.

Multi-signature wallets require multiple signatures (private keys) to approve transactions, increasing security.

🔧 Debug

advanced

What error does this multi-signature wallet code raise?

This Python-like pseudocode simulates a multi-signature wallet transaction approval. What error occurs when running it?

Blockchain / Solidity

owners = ['Alice', 'Bob', 'Charlie']
approvals = {'Alice': True, 'Bob': True}
required = 3
count = sum(approvals[owner] for owner in owners)
if count >= required:
    print('Transaction approved')
else:
    print('Transaction pending')

A KeyError because 'Charlie' is missing in approvals dictionary

B TypeError because sum cannot add booleans

C No error, prints 'Transaction approved'

D IndexError due to list access

💡 Hint

Check if all owners have approval entries.

The code tries to access approvals['Charlie'], which does not exist, causing a KeyError.

🚀 Application

advanced

How many transactions can be approved with this multi-signature setup?

A multi-signature wallet requires 2 out of 3 owners to approve a transaction. Given the following approvals, how many transactions are approved?

Blockchain / Solidity

transactions = [
  {'id': 1, 'approvals': {'Alice': True, 'Bob': True, 'Charlie': False}},
  {'id': 2, 'approvals': {'Alice': False, 'Bob': True, 'Charlie': True}},
  {'id': 3, 'approvals': {'Alice': False, 'Bob': False, 'Charlie': True}}
]
required = 2
approved_count = 0
for tx in transactions:
    count = sum(tx['approvals'].values())
    if count >= required:
        approved_count += 1
print(approved_count)

A 2

B 3

C 1

D 0

💡 Hint

Count transactions where approvals are at least 2.

Transactions 1 and 2 have 2 approvals each, so 2 transactions are approved.

📝 Syntax

expert

Which option correctly defines a multi-signature wallet approval function in Solidity?

Select the correct Solidity function syntax that checks if a transaction has enough approvals.

Blockchain / Solidity

function isApproved(uint txId) public view returns (bool) {
    uint count = 0;
    for (uint i = 0; i < owners.length; i++) {
        if (approvals[txId][owners[i]]) {
            count++;
        }
    }
    return count >= required;
}

A

function isApproved(uint txId) public view returns bool {
    uint count = 0;
    for (uint i = 0; i < owners.length; i++) {
        if (approvals[txId][owners[i]]) {
            count++;
        }
    }
    return count >= required;
}

B

function isApproved(uint txId) public returns (bool) {
    uint count = 0;
    for (uint i = 0; i <= owners.length; i++) {
        if (approvals[txId][owners[i]]) {
            count++;
        }
    }
    return count >= required;
}

C

function isApproved(uint txId) public view returns (bool) {
    uint count = 0;
    for (uint i = 0; i < owners.length; i++) {
        if (approvals[txId][owners[i]]) {
            count++;
        }
    }
    return count >= required;
}

D

function isApproved(uint txId) public view returns (bool) {
    uint count = 0;
    for (uint i = 0; i < owners.length; i++) {
        if (approvals[txId][owners[i]] == true) {
            count = count + 1;
        }
    }
    return count >= required;
}

💡 Hint

Check for correct function signature, loop bounds, and syntax.

Option C uses correct Solidity syntax: 'public view returns (bool)', loop with i < owners.length, and proper increment and return statements.