Why logic controls execution in Blockchain / Solidity - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a user has enough balance before sending tokens.

Blockchain / Solidity

if user_balance [1] amount_to_send:
    send_tokens()

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

A!=

B>=

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' will allow sending tokens even if balance is less, causing errors.

Using '==' is too strict; user can have more than the amount.

The condition must check if the user balance is greater than or equal to the amount to send to allow the transaction.

2fill in blank

medium

Complete the code to execute a smart contract function only if the sender is the owner.

Blockchain / Solidity

if sender_address [1] contract_owner:
    execute_function()

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

A!=

B>

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' would block the owner from executing the function.

Using '>' or '<' does not make sense for addresses.

The function should run only if the sender address matches the contract owner address.

3fill in blank

hard

Fix the error in the condition to prevent unauthorized access.

Blockchain / Solidity

if not (user_role [1] 'admin'):
    deny_access()

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

A==

B!=

Cin

Dnot in

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' inside with 'not' causes double negation and wrong logic.

Using 'in' or 'not in' is incorrect for string equality here.

The code denies access if the user role is not 'admin'. The condition uses 'not' outside, so inside it must check equality.

4fill in blank

hard

Fill both blanks to create a condition that executes only if the transaction amount is positive and sender is verified.

Blockchain / Solidity

if transaction_amount [1] 0 and sender_verified [2] True:
    process_transaction()

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

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' for amount allows zero or negative amounts.

Using '!=' for sender_verified allows unverified senders.

The transaction amount must be greater than zero and sender_verified must be exactly True to process the transaction.

5fill in blank

hard

Complete the code to create a dictionary comprehension that maps user IDs to their balances only if balance is positive and user is active.

Blockchain / Solidity

user_balances = {user_id: balance for user_id, balance, active in users if balance [1] 0 and active}

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

A.upper()

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Adding '.upper()' changes user_id to uppercase unnecessarily.

Using '==' instead of '>' allows zero balances.

The dictionary keys are user_id as is (no method call), values are balance as is, and the condition checks if balance is greater than zero.