Blockchain

# Install Foundry
curl -L https://foundry.paradigm.xyz | bash
foundryup

# Create a new project
forge init my-contract && cd my-contract

# Write a simple contract (src/Counter.sol already exists)
# Run tests
forge test -vvv

# Deploy to local Anvil node
anvil &
forge script script/Counter.s.sol --rpc-url http://localhost:8545 --broadcast

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.26;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

contract SecureVault is Ownable, ReentrancyGuard {
    mapping(address => uint256) private balances;

    event Deposit(address indexed user, uint256 amount);
    event Withdrawal(address indexed user, uint256 amount);

    constructor() Ownable(msg.sender) {}

    function deposit() external payable {
        balances[msg.sender] += msg.value;
        emit Deposit(msg.sender, msg.value);
    }

    // nonReentrant prevents reentrancy attacks
    function withdraw(uint256 amount) external nonReentrant {
        require(balances[msg.sender] >= amount, "Insufficient balance");
        balances[msg.sender] -= amount; // Update state BEFORE transfer
        (bool ok, ) = msg.sender.call{value: amount}("");
        require(ok, "Transfer failed");
        emit Withdrawal(msg.sender, amount);
    }
}