interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

contract TokenERC20 {
string public name;
string public symbol;
uint8 public decimals = 18; // 18 是建议的默认值
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);


function TokenERC20(uint256 initialSupply, string tokenName, string tokenSymbol) public {
totalSupply = initialSupply * 10 ** uint256(decimals);
balanceOf[msg.sender] = totalSupply;
name = tokenName;
symbol = tokenSymbol;
}


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;
Transfer(_from, _to, _value);
assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
}

function transfer(address _to, uint256 _value) public {
_transfer(msg.sender, _to, _value);
}

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
require(_value <= allowance[_from][msg.sender]); // Check allowance
allowance[_from][msg.sender] -= _value;
_transfer(_from, _to, _value);
return true;
}

function approve(address _spender, uint256 _value) public
returns (bool success) {
allowance[msg.sender][_spender] = _value;
return true;
}

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;
}
}

function burn(uint256 _value) public returns (bool success) {
require(balanceOf[msg.sender] >= _value);
balanceOf[msg.sender] -= _value;
totalSupply -= _value;
Burn(msg.sender, _value);
return true;
}

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;
Burn(_from, _value);
return true;
}
}