ERC-20 fungible token standard in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the total supply variable in an ERC-20 token contract.

Blockchain / Solidity

uint256 public [1];

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Aowner

Bbalance

CtotalSupply

Dallowance

Attempts:

3 left

💡 Hint

Common Mistakes

Using balance instead of totalSupply.

Using owner which is unrelated here.

The totalSupply variable holds the total number of tokens in circulation.

2fill in blank

medium

Complete the code to declare the transfer function signature in an ERC-20 token contract.

Blockchain / Solidity

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

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Ato

Brecipient

Cowner

Dspender

Attempts:

3 left

💡 Hint

Common Mistakes

Using spender which is for allowances.

Using owner which is the sender, not recipient.

The transfer function sends tokens to the to address.

3fill in blank

hard

Fix the error in the approve function signature to match the ERC-20 standard.

Blockchain / Solidity

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

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Aspender

Bcaller

Crecipient

Downer

Attempts:

3 left

💡 Hint

Common Mistakes

Using owner which is the token holder, not spender.

Using recipient which is not correct here.

The approve function sets allowance for the spender address.

4fill in blank

hard

Fill both blanks to complete the balanceOf function signature and return type.

Blockchain / Solidity

function balanceOf(address [1]) public view returns ([2]);

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Aaccount

Buint256

Cbool

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using bool as return type instead of uint256.

Using address as return type which is incorrect.

The balanceOf function takes an account address and returns its token balance as a uint256.

5fill in blank

hard

Fill all three blanks to complete the transferFrom function signature and return type.

Blockchain / Solidity

function transferFrom(address [1], address [2], uint256 [3]) public returns (bool);

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Asender

Brecipient

Camount

Dspender

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up spender with sender or recipient.

Using wrong parameter names that don't match the standard.

The transferFrom function moves amount tokens from sender to recipient.