Bitcoin Forum

pragma solidity ^0.4.18;

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; }

contract TokenERC20 {
    string public name;
    string public symbol;
    uint8 public decimals = 18;
    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 Approval(address indexed _owner, address indexed _spender, uint256 _value);

    event Burn(address indexed from, uint256 value);

    constructor(
        
        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;
        emit Transfer(_from, _to, _value);
    
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

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

   
    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;
        emit Approval(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;                  
        emit 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;                             
        emit Burn(_from, _value);
        return true;
    }
}