Security · medium

33. Checks-Effects-Interactions

Order matters when sending ether.

Implement `withdraw()` for `mapping(address => uint256) public balances` following CEI: check, zero out balance, then `call` to send ether.

Required in your answer: balances[msg.sender] = 0.call{value:require(ok

Compiles with solc in your browser

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Pull {
    mapping(address => uint256) public balances;
    function deposit() external payable { balances[msg.sender] += msg.value; }
    function withdraw() external {
        // TODO CEI
    }
}

Output appears here.

← 32. Reentrancy guard 34. Signature verification →