Why DeFi reimagines finance in Blockchain / Solidity - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a smart contract function that returns the contract's owner address.

Blockchain / Solidity

function getOwner() public view returns (address) {
    return [1];
}

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

Aowner

Bmsg.sender

Caddress(this)

Dtx.origin

Attempts:

3 left

💡 Hint

Common Mistakes

Returning msg.sender instead of owner

Returning address(this) which is the contract address

The function should return the stored owner address of the contract, not the caller or contract address.

2fill in blank

medium

Complete the code to emit an event when a token transfer happens.

Blockchain / Solidity

emit Transfer([1], to, amount);

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Afrom

Bowner

Cmsg.sender

Drecipient

Attempts:

3 left

💡 Hint

Common Mistakes

Using recipient or to instead of from

Using msg.sender which may differ from from in some cases

The Transfer event requires the sender's address as the first argument, which is from.

3fill in blank

hard

Fix the error in the function that checks if the caller is the owner.

Blockchain / Solidity

require([1] == owner, "Not authorized");

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Atx.origin

Bowner

Cmsg.sender

Daddress(this)

Attempts:

3 left

💡 Hint

Common Mistakes

Using tx.origin which can be spoofed

Using address(this) which is the contract address

The msg.sender is the address calling the function and should be checked against the owner.

4fill in blank

hard

Fill both blanks to create a mapping that tracks balances and a function to update them.

Blockchain / Solidity

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

function updateBalance(address user, [2] amount) public {
    balances[user] = amount;
}

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Auint256

Baddress

Cuint

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using bool instead of number

Using address as balance type

The balances mapping stores uint256 values, and the function parameter should be a uint256 amount.

5fill in blank

hard

Fill all three blanks to create a function that transfers tokens safely.

Blockchain / Solidity

function safeTransfer(address [1], address [2], uint [3]) public {
    require(balances[[1]] >= [3], "Insufficient balance");
    balances[[1]] -= [3];
    balances[[2]] += [3];
}

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

Afrom

Bto

Camount

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using user instead of from or to

Mixing parameter order

The function parameters should be from (sender), to (receiver), and amount (tokens to transfer).