XTRA.sol

pragma solidity ^0.4.12;



/**

 * @title SafeMath

 * @dev Math operations with safety checks that throw on error

 */

library SafeMath {

  function mul(uint256 a, uint256 b) internal constant returns (uint256) {

    uint256 c = a * b;

    assert(a == 0 || c / a == b);

    return c;

  }



  function div(uint256 a, uint256 b) internal constant returns (uint256) {

    // assert(b > 0); // Solidity automatically throws when dividing by 0

    uint256 c = a / b;

    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

    return c;

  }



  function sub(uint256 a, uint256 b) internal constant returns (uint256) {

    assert(b <= a);

    return a - b;

  }



  function add(uint256 a, uint256 b) internal constant returns (uint256) {

    uint256 c = a + b;

    assert(c >= a);

    return c;

  }

}





/**

 * @title Ownable

 * @dev The Ownable contract has an owner address, and provides basic authorization control

 * functions, this simplifies the implementation of "user permissions".

 */

contract Ownable {

  address public owner;





  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);





  /**

   * @dev The Ownable constructor sets the original `owner` of the contract to the sender

   * account.

   */

  function Ownable() {

    owner = msg.sender;

  }





  /**

   * @dev Throws if called by any account other than the owner.

   */

  modifier onlyOwner() {

    require(msg.sender == owner);

    _;

  }





  /**

   * @dev Allows the current owner to transfer control of the contract to a newOwner.

   * @param newOwner The address to transfer ownership to.

   */

  function transferOwnership(address newOwner) onlyOwner public {

    require(newOwner != address(0));

    OwnershipTransferred(owner, newOwner);

    owner = newOwner;

  }

}



/**

 * @title ERC20Basic

 * @dev Simpler version of ERC20 interface

 * @dev see https://github.com/ethereum/EIPs/issues/179

 */

contract ERC20Basic {

  uint256 public totalSupply;

  function balanceOf(address who) public constant returns (uint256);

  function transfer(address to, uint256 value) public returns (bool);

  event Transfer(address indexed from, address indexed to, uint256 value);

}





/**

 * @title Basic token

 * @dev Basic version of StandardToken, with no allowances.

 */

contract BasicToken is ERC20Basic {

  using SafeMath for uint256;



  mapping(address => uint256) balances;



  /**

  * @dev transfer token for a specified address

  * @param _to The address to transfer to.

  * @param _value The amount to be transferred.

  */

  function transfer(address _to, uint256 _value) public returns (bool) {

    require(_to != address(0));



    // SafeMath.sub will throw if there is not enough balance.

    balances[msg.sender] = balances[msg.sender].sub(_value);

    balances[_to] = balances[_to].add(_value);

    Transfer(msg.sender, _to, _value);

    return true;

  }



  /**

  * @dev Gets the balance of the specified address.

  * @param _owner The address to query the the balance of.

  * @return An uint256 representing the amount owned by the passed address.

  */

  function balanceOf(address _owner) public constant returns (uint256 balance) {

    return balances[_owner];

  }

}



/**

 * @title ERC20 interface

 * @dev see https://github.com/ethereum/EIPs/issues/20

 */

contract ERC20 is ERC20Basic {

  function allowance(address owner, address spender) public constant returns (uint256);

  function transferFrom(address from, address to, uint256 value) public returns (bool);

  function approve(address spender, uint256 value) public returns (bool);

  event Approval(address indexed owner, address indexed spender, uint256 value);

}





/**

 * @title Standard ERC20 token

 *

 * @dev Implementation of the basic standard token.

 * @dev https://github.com/ethereum/EIPs/issues/20

 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol

 */

contract StandardToken is ERC20, BasicToken {



  mapping (address => mapping (address => uint256)) allowed;





  /**

   * @dev Transfer tokens from one address to another

   * @param _from address The address which you want to send tokens from

   * @param _to address The address which you want to transfer to

   * @param _value uint256 the amount of tokens to be transferred

   */

  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {

    require(_to != address(0));



    uint256 _allowance = allowed[_from][msg.sender];



    // Check is not needed because sub(_allowance, _value) will already throw if this condition is not met

    // require (_value <= _allowance);



    balances[_from] = balances[_from].sub(_value);

    balances[_to] = balances[_to].add(_value);

    allowed[_from][msg.sender] = _allowance.sub(_value);

    Transfer(_from, _to, _value);

    return true;

  }



  /**

   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.

   *

   * Beware that changing an allowance with this method brings the risk that someone may use both the old

   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this

   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:

   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729

   * @param _spender The address which will spend the funds.

   * @param _value The amount of tokens to be spent.

   */

  function approve(address _spender, uint256 _value) public returns (bool) {

    allowed[msg.sender][_spender] = _value;

    Approval(msg.sender, _spender, _value);

    return true;

  }



  /**

   * @dev Function to check the amount of tokens that an owner allowed to a spender.

   * @param _owner address The address which owns the funds.

   * @param _spender address The address which will spend the funds.

   * @return A uint256 specifying the amount of tokens still available for the spender.

   */

  function allowance(address _owner, address _spender) public constant returns (uint256 remaining) {

    return allowed[_owner][_spender];

  }



  /**

   * approve should be called when allowed[_spender] == 0. To increment

   * allowed value is better to use this function to avoid 2 calls (and wait until

   * the first transaction is mined)

   * From MonolithDAO Token.sol

   */

  function increaseApproval (address _spender, uint _addedValue)

    returns (bool success) {

    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);

    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);

    return true;

  }



  function decreaseApproval (address _spender, uint _subtractedValue)

    returns (bool success) {

    uint oldValue = allowed[msg.sender][_spender];

    if (_subtractedValue > oldValue) {

      allowed[msg.sender][_spender] = 0;

    } else {

      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);

    }

    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);

    return true;

  }

}





/**

 * @title Burnable Token

 * @dev Token that can be irreversibly burned (destroyed).

 */

contract BurnableToken is StandardToken {



    event Burn(address indexed burner, uint256 value);



    /**

     * @dev Burns a specific amount of tokens.

     * @param _value The amount of token to be burned.

     */

    function burn(uint256 _value) public {

        require(_value > 0);

        require(_value <= balances[msg.sender]);

        // no need to require value <= totalSupply, since that would imply the

        // sender's balance is greater than the totalSupply, which *should* be an assertion failure



        address burner = msg.sender;

        balances[burner] = balances[burner].sub(_value);

        totalSupply = totalSupply.sub(_value);

        Burn(burner, _value);

    }

}



contract ExtraCreditToken  is BurnableToken, Ownable {



    string public constant name = "Extra Credit Token";

    string public constant symbol = "XTRA";

    uint public constant decimals = 8;

    uint256 public constant initialSupply = 600000000 * (10 ** uint256(decimals));



    // Constructor

    function ExtraCreditToken () {

        totalSupply = initialSupply;

        balances[msg.sender] = initialSupply; // Send all tokens to owner

    }



    

}