Interfaces in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an interface named IToken.

Blockchain / Solidity

interface [1] {
    function totalSupply() external view returns (uint256);
}

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AToken

BInterfaceToken

CTokenInterface

DIToken

Attempts:

3 left

💡 Hint

Common Mistakes

Using a name without the 'I' prefix for the interface.

The interface name should start with 'I' to indicate it's an interface, so 'IToken' is correct.

2fill in blank

medium

Complete the code to declare a function in the interface that transfers tokens.

Blockchain / Solidity

function transfer(address to, uint256 amount) external [1];

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Aview

Breturns (bool)

Cpure

Dpayable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'view' or 'pure' for a function that changes state.

The transfer function returns a boolean indicating success, so 'returns (bool)' is correct.

3fill in blank

hard

Fix the error in the interface function declaration for balanceOf.

Blockchain / Solidity

function balanceOf(address owner) external [1] returns (uint256);

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Aview

Bpayable

Cpure

Dexternal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'payable' or 'pure' incorrectly in the function declaration.

The balanceOf function only reads data, so it should be marked as 'view'.

4fill in blank

hard

Fill both blanks to declare an interface with two functions: approve and allowance.

Blockchain / Solidity

interface IToken {
    function approve(address spender, uint256 amount) external [1];
    function allowance(address owner, address spender) external [2] returns (uint256);
}

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Areturns (bool)

Bview

Cpure

Dpayable

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'view' and 'returns (bool)' in function declarations.

The approve function returns a boolean, so it uses 'returns (bool)'. The allowance function reads state, so it uses 'view'.

5fill in blank

hard

Fill all three blanks to declare an interface with functions: name, symbol, and decimals.

Blockchain / Solidity

interface IToken {
    function name() external [1] returns (string memory);
    function symbol() external [2] returns (string memory);
    function decimals() external [3] returns (uint8);
}

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

Aview

Bpure

Cpayable

Dreturns (string memory)

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pure' or 'payable' incorrectly for these read-only functions.

All these functions only read data, so they should be marked as 'view'.