contract TokenERC20 {
    uint256 public totalSupply;
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Burn(address indexed from, uint256 value);

    /**
     * Internal transfer, only can be called by this contract.
     */
    function _transfer(address _from, address _to, uint _value) internal {
        require(_to != 0x0);
        require(balanceOf[_from] >= _value);
        require(balanceOf[_to] + _value > balanceOf[_to]);
        uint previousBalances = balanceOf[_from] + balanceOf[_to];
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        emit Transfer(_from, _to, _value);
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    /**
     * Transfer tokens
     *
     * Send `_value` tokens to `_to` from your account.
     *
     * @param _to The address of the recipient.
     * @param _value the amount to send.
     */
    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }

    /**
     * Transfer tokens from other address.
     *
     * Send `_value` tokens to `_to` in behalf of `_from`.
     *
     * @param _from The address of the sender.
     * @param _to The address of the recipient.
     * @param _value the amount to send.
     */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

    /**
     * Set allowance for other address.
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf.
     *
     * @param _spender The address authorized to spend.
     * @param _value the max amount they can spend.
     */
    function approve(address _spender, uint256 _value) public
        returns (bool success) {
        require((_value == 0) || (allowance[msg.sender][_spender] == 0));
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    /**
     * Set allowance for other address and notify.
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the contract about it.
     *
     * @param _spender The address authorized to spend.
     * @param _value the max amount they can spend.
     * @param _extraData some extra information to send to the approved contract.
     */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

     /**
     * Destroy tokens
     *
     * Remove `_value` tokens from the system irreversibly.
     *
     * @param _value the amount of money to burn.
     */
    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);
        balanceOf[msg.sender] -= _value;
        totalSupply -= _value;
        emit Burn(msg.sender, _value);
        return true;
    }

    /**
     * Destroy tokens from other account.
     *
     * Remove `_value` tokens from the system irreversibly on behalf of `_from`.
     *
     * @param _from the address of the sender.
     * @param _value the amount of money to burn.
     */
    function burnFrom(address _from, uint256 _value) public returns (bool success) {
        require(balanceOf[_from] >= _value);
        require(_value <= allowance[_from][msg.sender]);
        balanceOf[_from] -= _value;
        allowance[_from][msg.sender] -= _value;
        totalSupply -= _value;
        emit Burn(_from, _value);
        return true;
    }
}
/// ERC20 standard，Define the minimum unit of money to 18 decimal places,
/// transfer out, destroy coins, others use your account spending pocket money.
function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }
/**
 * Set allowance for other address and notify.
 *
 * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the contract about it.
 *
 * @param _spender The address authorized to spend.
 * @param _value the max amount they can spend.
 * @param _extraData some extra information to send to the approved contract.
 */