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;

    // Triggered when tokens are transferred.
    event Transfer(address indexed from, address indexed to, uint256 value);

    // Triggered when spending allowance is set.
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    /**
     * Constructor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    function TokenERC20(uint256 _initialSupply, string _tokenName, string _tokenSymbol) internal {
        totalSupply = _initialSupply * 10 ** uint256(decimals);
        balanceOf[msg.sender] = totalSupply;
        name = _tokenName;
        symbol = _tokenSymbol;
    }

    /**
     * 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];

        // Perform the transfer
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
        Transfer(_from, _to, _value);
    }

    /**
     * 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 returns (bool success) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    /**
     * 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(_spender != 0x0);

        allowance[msg.sender][_spender] = _value;
        Approval(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)) {
            return false;
        }

        spender.receiveApproval(msg.sender, _value, this, _extraData);
        return true;
    }
}
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;
}

/**
 * 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
 */