Balance checking in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the balance of an account.

Blockchain / Solidity

balance = blockchain.get_balance([1])

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

Awallet_key

Bblock_number

Caccount_address

Dtransaction_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using block number instead of account address

Using transaction ID instead of account address

The get_balance function requires the account_address to return the balance of that account.

2fill in blank

medium

Complete the code to check if the balance is greater than zero.

Blockchain / Solidity

if balance [1] 0:
    print('Balance is positive')

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

A<

B>

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of >

Using == which checks equality, not greater than

To check if the balance is positive, use the greater than operator > to compare with zero.

3fill in blank

hard

Fix the error in the code to correctly fetch the balance.

Blockchain / Solidity

balance = blockchain.[1](account_address)

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

Aretrieve_balance

Bbalance_of

Cfetch_balance

Dget_balance

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that do not exist in the blockchain API

Typo in method name

The correct method to get the balance is get_balance. Other options are invalid method names.

4fill in blank

hard

Fill both blanks to create a dictionary of account balances for accounts with balance greater than 100.

Blockchain / Solidity

balances = {account: blockchain.[1](account) for account in accounts if blockchain.[2](account) > 100}

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

Aget_balance

Bfetch_balance

Dretrieve_balance

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names for fetching balance

Using a method that does not exist

Use get_balance consistently to fetch balances in both places.

5fill in blank

hard

Fill all three blanks to create a dictionary of uppercase account names and their balances if balance is above 50.

Blockchain / Solidity

result = {account.[1](): blockchain.[2](account) for account in accounts if blockchain.[3](account) > 50}

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

Aupper

Bget_balance

Dfetch_balance

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent method names for balance fetching

Using wrong string method for uppercase

Use upper() to convert account names to uppercase and get_balance to fetch balances consistently.

Practice

1.

What does balance checking in blockchain primarily tell you?

easy

A. The private key of a wallet

B. The transaction history of an address

C. How much cryptocurrency an address currently holds

D. The mining difficulty of the blockchain

Solution

1. Step 1: Understand the purpose of balance checking

   Balance checking is used to find out the amount of cryptocurrency held by a blockchain address.

2. Step 2: Differentiate from other blockchain data

   Transaction history, private keys, and mining difficulty are different concepts unrelated to balance checking.

3. Final Answer:

   How much cryptocurrency an address currently holds -> Option C

4. Quick Check:

   Balance checking = cryptocurrency amount [OK]

Hint: Balance checking shows funds held by an address [OK]

Common Mistakes:

• Confusing balance with transaction history
• Thinking balance reveals private keys
• Mixing balance with blockchain mining info

2.

Which of the following is the correct way to call a function getBalance for an address addr in a blockchain library?

?

easy

A. getBalance(addr)

B. getBalance = addr

C. getBalance.addr()

D. getBalance->addr()

Solution

1. Step 1: Identify correct function call syntax

   In most programming languages, calling a function with an argument uses parentheses: functionName(argument).

2. Step 2: Check each option

   getBalance(addr) uses correct syntax: getBalance(addr). Options A, C, and D use invalid or incorrect syntax.

3. Final Answer:

   getBalance(addr) -> Option A

4. Quick Check:

   Function call syntax = getBalance(addr) [OK]

Hint: Function calls use parentheses with arguments [OK]

Common Mistakes:

• Using assignment instead of function call
• Using dot notation incorrectly for function calls
• Using arrow notation which is not valid here

3.

Given this JavaScript code snippet using a blockchain API:

async function check() {
  const balance = await blockchainAPI.getBalance('0x123');
  console.log(balance);
}
check();

What will be printed if the address has 500 tokens?

medium

A. undefined

B. 500

C. Error: getBalance is not a function

D. null

Solution

1. Step 1: Understand async/await usage

   The function uses await to get the balance asynchronously, so balance will hold the returned value.

2. Step 2: Check what is logged

   console.log(balance) will print the balance value, which is 500 tokens for the given address.

3. Final Answer:

   500 -> Option B

4. Quick Check:

   Async balance fetch = 500 [OK]

Hint: Await returns the actual balance value [OK]

Common Mistakes:

• Ignoring async and expecting immediate value
• Assuming undefined if await is missing
• Confusing error messages with correct output

4.

Find the error in this Python code that tries to get a balance:

def get_balance(address):
    balance = blockchain.getBalance(address)
    return balance

print(get_balance)

medium

A. Using print instead of return

B. Incorrect function name getBalance

C. Missing import statement for blockchain

D. Missing parentheses when calling get_balance in print

Solution

1. Step 1: Check how get_balance is used in print

   The code prints get_balance without parentheses, so it prints the function object, not the result.

2. Step 2: Correct usage to call the function

   Adding parentheses and an argument like print(get_balance('0xabc')) calls the function and prints the balance.

3. Final Answer:

   Missing parentheses when calling get_balance in print -> Option D

4. Quick Check:

   Function call needs () [OK]

Hint: Call functions with () to get results [OK]

Common Mistakes:

• Printing function name instead of calling it
• Assuming function runs without parentheses
• Ignoring required function arguments

5.

You want to check balances of multiple addresses and store them in a dictionary in Python. Which code correctly does this?

addresses = ['0x1', '0x2', '0x3']
balances = {}
for addr in addresses:
    balances[addr] = blockchain.getBalance(addr)
print(balances)

hard

A. This code correctly stores balances for each address in a dictionary

B. This code will cause a syntax error due to missing colon

C. This code overwrites balances instead of storing all

D. This code does not call getBalance correctly

Solution

1. Step 1: Analyze the loop and dictionary usage

   The for loop iterates over each address and assigns the balance to balances[addr], storing all balances.

2. Step 2: Check syntax and function call

   Syntax is correct with colon and indentation; getBalance is called properly with each address.

3. Final Answer:

   This code correctly stores balances for each address in a dictionary -> Option A

4. Quick Check:

   Loop + dict assignment = correct balances [OK]

Hint: Use a loop to assign balances to dictionary keys [OK]

Common Mistakes:

• Forgetting colon after for statement
• Overwriting dictionary instead of adding keys
• Calling getBalance without argument