ERC-20 implementation 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 contract.

Blockchain / Solidity

uint256 public [1];

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Aamount

Bbalance

Cowner

DtotalSupply

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names like balance or owner instead of totalSupply.

The totalSupply variable holds the total number of tokens in circulation in an ERC-20 contract.

2fill in blank

medium

Complete the code to define the balance mapping for token holders.

Blockchain / Solidity

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

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Auint256

Bstring

Cbool

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using bool or address instead of uint256.

The balances mapping stores the token balance (as uint256) for each address.

3fill in blank

hard

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

Blockchain / Solidity

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

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Afrom

Brecipient

Cto

Dspender

Attempts:

3 left

💡 Hint

Common Mistakes

Using from or spender instead of to.

The ERC-20 transfer function uses to as the parameter name for the recipient address.

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 maps an owner address to a spender address to the allowed token amount (uint256).

5fill in blank

hard

Fill all three blanks to complete the transfer function body that updates balances and emits Transfer event.

Blockchain / Solidity

require(balances[msg.sender] >= [1], "Insufficient balance");
balances[msg.sender] -= [2];
balances[[3]] += amount;
emit Transfer(msg.sender, [3], amount);
return true;

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

Aamount

Bto

Dfrom

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names like from or mixing up amount and to.

The function checks if the sender has enough amount, subtracts it, adds it to the recipient to, emits the Transfer event, and returns true.