Transaction confirmation handling in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this transaction confirmation check?

Consider this pseudocode for checking transaction confirmations on a blockchain. What will be the printed output?

Blockchain / Solidity

confirmations = 3
required_confirmations = 6
if confirmations >= required_confirmations:
    print("Transaction confirmed")
else:
    print(f"Waiting for {required_confirmations - confirmations} more confirmations")

A Waiting for 3 more confirmations

B Transaction confirmed

C Waiting for 6 more confirmations

D Error: variable not defined

💡 Hint

Check if the current confirmations meet or exceed the required confirmations.

The code compares current confirmations (3) with required (6). Since 3 < 6, it prints the waiting message with the difference (6-3=3).

🧠 Conceptual

intermediate

Which statement best describes transaction confirmation?

In blockchain, what does a transaction confirmation mean?

A The transaction has been included in a block and that block is part of the longest chain.

B The transaction is waiting in the mempool to be mined.

C The transaction has been rejected by the network.

D The transaction is being broadcast to peers.

💡 Hint

Think about when a transaction is considered secure and irreversible.

A confirmation means the transaction is inside a block that is accepted as part of the main blockchain, making it harder to reverse.

🔧 Debug

advanced

Why does this confirmation count code raise an error?

This code snippet is intended to count confirmations but raises an error. Identify the cause.

Blockchain / Solidity

def check_confirmations(tx_hash):
    confirmations = blockchain.get_confirmations(tx_hash)
    if confirmations > 0:
        return confirmations
    else:
        return 0

A IndentationError due to wrong indentation

B NameError because blockchain is not defined

C TypeError because confirmations is not an integer

D SyntaxError due to missing colon after if statement

💡 Hint

Check the syntax of the if statement line.

The if statement is missing a colon at the end, causing a SyntaxError.

🚀 Application

advanced

How many confirmations does this code wait for before proceeding?

Given this code snippet, how many confirmations does it require before printing 'Confirmed'?

Blockchain / Solidity

required_confirmations = 12
current_confirmations = 10
while current_confirmations < required_confirmations:
    print(f"Current: {current_confirmations}, waiting...")
    current_confirmations += 1
print("Confirmed")

A 11

B 12

C 2

D 10

💡 Hint

Look at the condition that stops the loop.

The loop runs until current_confirmations reaches 12, so it waits for 12 confirmations before printing 'Confirmed'.

❓ Predict Output

expert

What is the output of this asynchronous confirmation checker?

This JavaScript async function checks confirmations. What will it print?

Blockchain / Solidity

async function checkTx(txId) {
  let confirmations = 0;
  while (confirmations < 3) {
    confirmations++;
    console.log(`Confirmations: ${confirmations}`);
    await new Promise(resolve => setTimeout(resolve, 100));
  }
  console.log('Transaction confirmed');
}
checkTx('abc123');

A Confirmations: 0\nConfirmations: 1\nConfirmations: 2

B Transaction confirmed

C Confirmations: 1\nConfirmations: 2\nConfirmations: 3\nTransaction confirmed

D SyntaxError due to await outside async function

💡 Hint

The function increments confirmations and waits 100ms each loop until 3 confirmations.

The loop prints confirmations 1, 2, 3 with delays, then prints 'Transaction confirmed'.