Sidechains in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this sidechain token transfer simulation?

Consider a simple Python simulation of a sidechain token transfer. What will be printed after running the code?

Blockchain / Solidity

class Sidechain:
    def __init__(self):
        self.balances = {"main": 1000, "side": 0}

    def lock_tokens(self, amount):
        if self.balances["main"] >= amount:
            self.balances["main"] -= amount
            self.balances["side"] += amount
            print(f"Locked {amount} tokens to sidechain")
        else:
            print("Insufficient tokens on main chain")

    def unlock_tokens(self, amount):
        if self.balances["side"] >= amount:
            self.balances["side"] -= amount
            self.balances["main"] += amount
            print(f"Unlocked {amount} tokens to main chain")
        else:
            print("Insufficient tokens on sidechain")

sc = Sidechain()
sc.lock_tokens(300)
sc.unlock_tokens(100)
print(sc.balances)

A {'main': 800, 'side': 200}

B {'main': 700, 'side': 300}

C {'main': 900, 'side': 100}

D {'main': 1000, 'side': 0}

💡 Hint

Think about how tokens move between main and sidechain balances after locking and unlocking.

Initially, 1000 tokens are on the main chain. Locking 300 moves 300 tokens to the sidechain, reducing main to 700 and side to 300. Then unlocking 100 moves 100 tokens back to main, so main becomes 800 and side 200.

🧠 Conceptual

intermediate

Which statement best describes a sidechain's purpose?

Choose the option that correctly explains why sidechains are used in blockchain technology.

A Sidechains are used to permanently store all transaction data from the main blockchain to increase security.

B Sidechains allow assets to move between different blockchains to improve scalability and add features without changing the main chain.

C Sidechains replace the main blockchain entirely to provide a faster consensus mechanism.

D Sidechains are private blockchains that cannot interact with the main blockchain.

💡 Hint

Think about how sidechains help with scalability and flexibility.

Sidechains enable assets to move between chains, allowing new features and scalability improvements without altering the main blockchain.

🔧 Debug

advanced

Identify the error in this sidechain asset locking code

The following Python code simulates locking assets to a sidechain. It raises an error when run. What is the cause?

Blockchain / Solidity

class Sidechain:
    def __init__(self):
        self.balances = {"main": 500, "side": 0}

    def lock(self, amount):
        if self.balances["main"] >= amount:
            self.balances["main"] -= amount
            self.balances["side"] += amount
        else:
            print("Not enough tokens")

sc = Sidechain()
sc.lock(600)

A SyntaxError due to missing colon after else statement

B KeyError because 'side' key does not exist in balances

C TypeError because balances is not a dictionary

D RuntimeError due to negative balance

💡 Hint

Check the syntax of the if-else block carefully.

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

📝 Syntax

advanced

Which option correctly implements a sidechain asset withdrawal function?

Choose the code snippet that correctly defines a method to withdraw tokens from a sidechain back to the main chain.

A

def withdraw(self, amount):
    if self.balances['side'] >= amount:
        self.balances['side'] -= amount
        self.balances['main'] =+ amount
    else:
        print('Insufficient sidechain balance')

B

def withdraw(self, amount):
    if self.balances['side'] > amount:
        self.balances['side'] -= amount
        self.balances['main'] += amount
    else
        print('Insufficient sidechain balance')

C

def withdraw(self, amount):
    if self.balances['side'] >= amount
        self.balances['side'] -= amount
        self.balances['main'] += amount
    else:
        print('Insufficient sidechain balance')

D

def withdraw(self, amount):
    if self.balances['side'] >= amount:
        self.balances['side'] -= amount
        self.balances['main'] += amount
    else:
        print('Insufficient sidechain balance')

💡 Hint

Look for correct syntax and correct operators.

Option D uses correct syntax with colon after if, correct comparison operator, and correct += operator. Others have syntax errors or wrong operators.

🚀 Application

expert

How many tokens remain on the sidechain after these operations?

Given the following sequence of operations on a sidechain, how many tokens remain on the sidechain?

sc = Sidechain()
sc.lock_tokens(400)
sc.unlock_tokens(150)
sc.lock_tokens(100)
sc.unlock_tokens(200)
print(sc.balances)

Blockchain / Solidity

class Sidechain:
    def __init__(self):
        self.balances = {"main": 1000, "side": 0}

    def lock_tokens(self, amount):
        if self.balances["main"] >= amount:
            self.balances["main"] -= amount
            self.balances["side"] += amount

    def unlock_tokens(self, amount):
        if self.balances["side"] >= amount:
            self.balances["side"] -= amount
            self.balances["main"] += amount

A 350

B 100

C 150

D 250

💡 Hint

Track each lock and unlock step carefully to update balances.

Start with main=1000, side=0. Lock 400: main=600, side=400. Unlock 150: main=750, side=250. Lock 100: main=650, side=350. Unlock 200: main=850, side=150. Final side balance is 150.