1. 添加Approval和TransferFrom功能
   ERC-20標準中的approve和transferFrom是用於允許第三方（如智能合約）代表代幣持有者進行交易的功能，對於應用場景去中心化金融（DeFi）中的代幣托管與自動化交易很重要。

mapping(address => mapping(address => uint256)) public allowance;

function approve(address _spender, uint256 _value) public returns (bool success) {
    allowance[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
}

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
    require(_value <= balanceOf[_from], "Insufficient balance");
    require(_value <= allowance[_from][msg.sender], "Allowance exceeded");

    balanceOf[_from] -= _value;
    balanceOf[_to] += _value;
    allowance[_from][msg.sender] -= _value;

    emit Transfer(_from, _to, _value);
    return true;
}

2. SafeMath防止溢出問題
   在Solidity中進行數學運算時，整數溢出問題可能導致安全漏洞，引入SafeMath可以防止溢出問題。

import "@openzeppelin/contracts/utils/math/SafeMath.sol";

contract MyToken {
    using SafeMath for uint256;
}