整数溢出

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.17;

contract Token {
  // uint8 0 - 255
  mapping(address => uint8) balances;

  constructor() {
    balances[msg.sender] = 250;
  }
  
  function deposit(uint8 _value) public returns (bool) {
    unchecked{
        balances[msg.sender] += _value;
    }
    return true;
  }

  function balanceOf(address _owner) public view returns (uint balance) {
    return balances[_owner];
  }
}