1_SimpleToken.sol

/* This program is free software. It comes without any warranty, to
the extent permitted by applicable law. You can redistribute it
and/or modify it under the terms of the Do What The Fuck You Want
To Public License, Version 2, as published by Sam Hocevar. See
http://www.wtfpl.net/ for more details. */

/* These contracts are examples of contracts with vulnerabilities in order to practice your hacking skills.
DO NOT USE THEM OR GET INSPIRATION FROM THEM TO MAKE CODE USED IN PRODUCTION */

pragma solidity ^0.4.10;

// Simple token you can buy and send.
contract SimpleToken{
    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]!=0); // You must have some tokens.

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

}