Staking mechanisms in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a staking balance mapping in Solidity.

Blockchain / Solidity

mapping(address => uint256) public [1];

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

AstakeAmount

BstakingBalance

Cbalances

DuserStake

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that does not clearly represent staking balances.

Forgetting to specify the mapping key or value types.

The stakingBalance mapping is commonly used to track how much each address has staked.

2fill in blank

medium

Complete the code to allow users to stake tokens by updating their balance.

Blockchain / Solidity

function stakeTokens(uint256 _amount) public {
    require(_amount > 0, "Amount must be greater than zero");
    [1][msg.sender] += _amount;
}

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

AstakingBalance

Bbalances

CuserStake

DstakeAmount

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong mapping name.

Not using msg.sender as the key.

The stakingBalance mapping is updated to add the staked amount for the sender.

3fill in blank

hard

Fix the error in the function that allows users to unstake their tokens.

Blockchain / Solidity

function unstakeTokens() public {
    uint256 balance = [1][msg.sender];
    require(balance > 0, "No tokens to unstake");
    stakingBalance[msg.sender] = 0;
    // Transfer tokens back to user
}

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

AstakingBalance

BuserStake

Cbalances

DstakeAmount

Attempts:

3 left

💡 Hint

Common Mistakes

Using a mapping name that does not exist or is inconsistent.

Not checking the correct balance before unstaking.

The correct mapping to check the user's staked tokens is stakingBalance.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps user addresses to their staked amounts greater than zero.

Blockchain / Solidity

activeStakes = {address: amount for (address, amount) in [1].items() if amount [2] 0};

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

AstakingBalance

B>

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Using a mapping name that does not exist.

This comprehension filters stakingBalance to include only users with amounts greater than zero.

5fill in blank

hard

Fill all three blanks to calculate rewards for each user with staked tokens above a threshold.

Blockchain / Solidity

rewards = { [1]: [2] * rewardRate for ([3], amount) in stakingBalance.items() if amount > threshold };

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

Auser

Bamount

Dstake

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up variable names in the comprehension.

Using incorrect variable names for keys or values.

The comprehension uses user as the key, multiplies amount by rewardRate, and iterates over stakingBalance items with user and amount.

Practice

1. What is the main purpose of staking tokens in a blockchain network?

easy

A. To create new tokens instantly

B. To transfer tokens to another user

C. To help secure the network and earn rewards

D. To delete tokens from the blockchain

Solution

1. Step 1: Understand staking concept

   Staking means locking tokens to support blockchain security.

2. Step 2: Identify staking benefits

   Users earn rewards for staking, helping network stability.

3. Final Answer:

   To help secure the network and earn rewards -> Option C

4. Quick Check:

   Staking = Security + Rewards [OK]

Hint: Staking locks tokens to secure network and gain rewards [OK]

Common Mistakes:

• Confusing staking with token transfer
• Thinking staking creates new tokens
• Believing staking deletes tokens

2. Which of the following is the correct way to represent staking tokens in a smart contract pseudocode?

easy

A. stakeAmount = userBalance - lockedTokens

B. lockedTokens = stakeAmount + userBalance

C. userBalance = stakeAmount + lockedTokens

D. lockedTokens = stakeAmount

Solution

1. Step 1: Understand staking variables

   Locked tokens represent the amount staked by user.

2. Step 2: Match correct assignment

   lockedTokens should equal stakeAmount to show tokens locked.

3. Final Answer:

   lockedTokens = stakeAmount -> Option D

4. Quick Check:

   Locked tokens = stake amount [OK]

Hint: Locked tokens equal the stake amount directly [OK]

Common Mistakes:

• Adding stakeAmount to userBalance incorrectly
• Subtracting lockedTokens from userBalance wrongly
• Mixing variable roles in assignment

3. Consider this pseudocode for calculating staking rewards:

reward = stakedAmount * rewardRate * stakingDuration
print(reward)

If stakedAmount = 100, rewardRate = 0.05, and stakingDuration = 10, what is the output?

medium

A. 50

B. 5

C. 0.5

D. 500

Solution

1. Step 1: Substitute values into formula

   reward = 100 * 0.05 * 10

2. Step 2: Calculate reward

   100 * 0.05 = 5; then 5 * 10 = 50

3. Final Answer:

   50 -> Option A

4. Quick Check:

   100 * 0.05 * 10 = 50 [OK]

Hint: Multiply all values stepwise: amount * rate * duration [OK]

Common Mistakes:

• Multiplying only two values
• Confusing rewardRate as 5 instead of 0.05
• Adding values instead of multiplying

4. The following pseudocode has an error. What is the problem?

function stakeTokens(userBalance, stakeAmount) {
  if (stakeAmount > userBalance) {
    return "Error: Not enough balance";
  }
  lockedTokens = stakeAmount;
  userBalance = userBalance - stakeAmount;
  return lockedTokens;
}

medium

A. lockedTokens is not declared before assignment

B. The function does not return userBalance

C. The if condition should be stakeAmount < userBalance

D. The subtraction should add stakeAmount instead

Solution

1. Step 1: Check variable declarations

   lockedTokens is assigned without declaration, causing error in strict languages.

2. Step 2: Understand variable scope

   lockedTokens should be declared (e.g., let or var) before use.

3. Final Answer:

   lockedTokens is not declared before assignment -> Option A

4. Quick Check:

   Undeclared variable causes error [OK]

Hint: Always declare variables before assigning [OK]

Common Mistakes:

• Ignoring variable declaration errors
• Misreading the if condition logic
• Thinking subtraction should be addition

5. You want to write a function that calculates total rewards for multiple users staking different amounts for different durations. Which approach correctly applies staking mechanisms?

hard

A. Add all staked amounts first, then multiply by rewardRate and total duration

B. Loop through each user, calculate reward = stakedAmount * rewardRate * duration, then sum all rewards

C. Calculate reward only for the user with the highest stake

D. Multiply rewardRate by duration only once, ignoring staked amounts

Solution

1. Step 1: Understand reward calculation per user

   Each user's reward depends on their own stake and duration.

2. Step 2: Sum individual rewards for total

   Calculate each reward separately, then add for total rewards.

3. Final Answer:

   Loop through each user, calculate reward = stakedAmount * rewardRate * duration, then sum all rewards -> Option B

4. Quick Check:

   Calculate per user, then sum [OK]

Hint: Calculate rewards individually, then add for total [OK]

Common Mistakes:

• Summing stakes before multiplying
• Ignoring individual durations
• Calculating reward for only one user