contract StandardToken is ERC20, BasicToken {

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

require(_value <= balances[_from]);

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

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

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

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

emit 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;

emit 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

view

returns (uint256)

{

return allowed[_owner][_spender];

}

/**

* @dev Increase the amount of tokens that an owner allowed to a 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

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

* @param _addedValue The amount of tokens to increase the allowance by.

*/

function increaseApproval(

address _spender,

uint _addedValue

)

public

returns (bool)

{

allowed[msg.sender][_spender] = (

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

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

return true;

}

/**

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

*

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

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

* the first transaction is mined)

* From MonolithDAO Token.sol

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

* @param _subtractedValue The amount of tokens to decrease the allowance by.

*/

function decreaseApproval(

address _spender,

uint _subtractedValue

)

public

returns (bool)

{

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

if (_subtractedValue > oldValue) {

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

} else {

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

}

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

return true;

}

}
/**
 
 * @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
 
 */
function transferFrom(

address _from,

address _to,

uint256 _value

)

public

returns (bool)

{

require(_to != address(0));

require(_value <= balances[_from]);

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

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

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

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

emit Transfer(_from, _to, _value);

return true;

}

/**
 
 * @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
 
 */