6_Token.sol

contract Token {
    mapping(address => uint) public balances;

    /// @dev Buy token at the price of 1ETH/token.
    function buyToken() payable {
        balances[msg.sender]+=msg.value / 1 ether;
    }

    /** @dev Send token.
     *  @param _recipient The recipient.
     *  @param _amount The amount to send.
     */
    function sendToken(address _recipient, uint _amount) {
        require(balances[msg.sender]>=_amount); // You must have some tokens.

        balances[msg.sender]-=_amount;
        balances[_recipient]+=_amount;
    }

    /** @dev Send all tokens.
     *  @param _recipient The recipient.
     */
    function sendAllTokens(address _recipient) {
        balances[_recipient]=+balances[msg.sender];
        balances[msg.sender]=0;
    }

}