contract Token is IToken, Owned, Utils {
    /* 公共变量 */
    string public standard = '';
    string public name = ''; //代币名称
    string public symbol = ''; //代币符号比如'$'
    uint8 public decimals = 0;  //代币单位
    uint256 public totalSupply = 0; //代币总量

    /*记录所有余额的映射*/
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

    /* 在区块链上创建一个事件，用以通知客户端*/
    event Transfer(address indexed from, address indexed to, uint256 value);  //转帐通知事件
    event Approval(address indexed _owner, address indexed _spender, uint256 _value); //设置允许用户支付最大金额通知

    function Token() public 
    {
        name = 'MCNC健康树';
        symbol = 'MCNC';
        decimals = 8;
        totalSupply = 2000000000 * 10 ** uint256(decimals);

        balanceOf[owner] = totalSupply;
    }

    function _transfer(address _from, address _to, uint256 _value)
      internal
      validAddress(_from)
      validAddress(_to)
    {

      require(balanceOf[_from] >= _value);
      require(balanceOf[_to] + _value > balanceOf[_to]);
      uint previousBalances = safeAdd(balanceOf[_from], balanceOf[_to]);
      balanceOf[_from] = safeSub(balanceOf[_from], _value);
      balanceOf[_to] += safeAdd(balanceOf[_to], _value);

      emit Transfer(_from, _to, _value);

      assert(balanceOf[_from] + balanceOf[_to] == previousBalances);

    }

    function transfer(address _to, uint256 _value)
      public
      validAddress(_to)
      returns (bool)
    {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value)
        public
        validAddress(_from)
        validAddress(_to)
        returns (bool)
    {
        //检查发送者是否拥有足够余额支出的设置
        require(_value <= allowance[_from][msg.sender]);   // Check allowance

        allowance[_from][msg.sender] -= safeSub(allowance[_from][msg.sender], _value);

        _transfer(_from, _to, _value);

        return true;
    }

    function approve(address _spender, uint256 _value)
        public
        validAddress(_spender)
        returns (bool success)
    {

        require(_value == 0 || allowance[msg.sender][_spender] == 0);

        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
}
function Token() public 
    {
        name = 'MCNC健康树';
        symbol = 'MCNC';
        decimals = 8;
        totalSupply = 2000000000 * 10 ** uint256(decimals);

        balanceOf[owner] = totalSupply;
    }
//设置允许用户支付最大金额通知