Transfer and approve flow in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the transfer function signature.

Blockchain / Solidity

function transfer(address [1], uint256 amount) public returns (bool);

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Afrom

Bto

Cspender

Downer

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'from' instead of 'to' for the recipient address.

The transfer function sends tokens to the to address.

2fill in blank

medium

Complete the code to approve a spender to spend tokens.

Blockchain / Solidity

function approve(address [1], uint256 amount) public returns (bool);

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Aspender

Bowner

Crecipient

Dto

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'owner' instead of 'spender'.

The approve function allows the spender to spend tokens on behalf of the owner.

3fill in blank

hard

Fix the error in the transferFrom function parameter name.

Blockchain / Solidity

function transferFrom(address [1], address to, uint256 amount) public returns (bool);

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Ato

Bspender

Cowner

Dfrom

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'to' or 'spender' instead of 'from'.

The transferFrom function moves tokens from the from address to to.

4fill in blank

hard

Fill both blanks to complete the allowance mapping declaration.

Blockchain / Solidity

mapping([1] => mapping([2] => uint256)) private _allowances;

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Aaddress

Buint256

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using uint256 or bool as keys instead of address.

The _allowances mapping tracks how many tokens an owner allows a spender to use. Both keys are addresses.

5fill in blank

hard

Fill all three blanks to complete the transferFrom function body snippet.

Blockchain / Solidity

require(_allowances[[1]][[2]] >= amount, "Allowance too low");
_allowances[[3]][[2]] -= amount;

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Afrom

Bspender

Cto

Downer

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'to' and 'spender' keys.

The allowance is checked and reduced for the from owner and spender. The from address's allowance is decreased.