pragma solidity ^0.4.18;


contract SafeMath {
//internals

function safeMul(uint a, uint b) internal returns(uint) {
uint c = a * b;
assert(a == 0 || c / a == b);
return c;
}

function safeSub(uint a, uint b) internal returns(uint) {
assert(b <= a);
return a - b;
}

function safeAdd(uint a, uint b) internal returns(uint) {
uint c = a + b;
assert(c >= a && c >= b);
return c;
}
}




contract owned {
address public owner;

function owned() public {
owner = msg.sender;
}

modifier onlyOwner {
require(msg.sender == owner);
_;
}

function transferOwnership(address newOwner) onlyOwner public {
owner = newOwner;
}
}

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

contract TokenERC20 is SafeMath {
// Public variables of the token
string public name;
string public symbol;
uint8 public decimals = 8;
//
uint256 public totalSupply;


// This creates an array with all balances
mapping (address => uint256) public balanceOf;
mapping (address => mapping (address => uint256)) public allowance;

// This generates a public event on the blockchain that will notify clients
event Transfer(address indexed from, address indexed to, uint256 value);

// This notifies clients about the amount burnt
event Burn(address indexed from, uint256 value);

/**
* Constrctor function
*
* Initializes contract with initial supply tokens to the creator of the contract
*/
function TokenERC20(
uint256 initialSupply,
string tokenName,
string tokenSymbol
) public {
totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
balanceOf[msg.sender] = totalSupply;                // Give the creator all initial tokens
name = tokenName;                                   // Set the name for display purposes
symbol = tokenSymbol;                               // Set the symbol for display purposes
}

/**
* Internal transfer, only can be called by this contract
*/
function _transfer(address _from, address _to, uint _value) internal {
// Prevent transfer to 0x0 address. Use burn() instead
require(_to != 0x0);
// Check if the sender has enough
require(balanceOf[_from] >= _value);
// Check for overflows
require(safeAdd(balanceOf[_to], _value) > balanceOf[_to]);
// Save this for an assertion in the future
uint previousBalances = safeAdd(balanceOf[_from], balanceOf[_to]);
// Subtract from the sender
balanceOf[_from] = safeSub(balanceOf[_from], _value);
// Add the same to the recipient
balanceOf[_to] = safeAdd(balanceOf[_to], _value);
Transfer(_from, _to, _value);
// Asserts are used to use static analysis to find bugs in your code. They should never fail
assert(safeAdd(balanceOf[_from], balanceOf[_to]) == previousBalances);
}

/**
* 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 {
_transfer(msg.sender, _to, _value);
}

/**
* 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]);     // Check allowance
allowance[_from][msg.sender] = safeSub(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) {
allowance[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)) {
spender.receiveApproval(msg.sender, _value, this, _extraData);
return true;
}
}



/**
* Destroy tokens
*
* Remove `_value` tokens from the system irreversibly
*
* @param _value the amount of money to burn
*/
function burn(uint256 _value) public returns (bool success) {
require(balanceOf[msg.sender] >= _value);   // Check if the sender has enough
balanceOf[msg.sender] = safeSub(balanceOf[msg.sender], _value);            // Subtract from the sender
totalSupply = safeSub(totalSupply,_value);                      // Updates totalSupply
Burn(msg.sender, _value);
return true;
}



/**
* Destroy tokens from other ccount
*
* Remove `_value` tokens from the system irreversibly on behalf of `_from`.
*
* @param _from the address of the sender
* @param _value the amount of money to burn
*/
function burnFrom(address _from, uint256 _value) public returns (bool success) {
require(balanceOf[_from] >= _value);                // Check if the targeted balance is enough
require(_value <= allowance[_from][msg.sender]);    // Check allowance
balanceOf[_from] = safeSub(balanceOf[_from], _value);                         // Subtract from the targeted balance
allowance[_from][msg.sender] =safeSub(allowance[_from][msg.sender],_value);             // Subtract from the sender's allowance
totalSupply =safeSub(totalSupply,_value);                              // Update totalSupply
Burn(_from, _value);
return true;
}
}

/******************************************/
/*       ADVANCED TOKEN STARTS HERE       */
/******************************************/

contract BTCx is owned, TokenERC20  {

address public ico;

mapping (address => bool) public frozenAccount;

/* This generates a public event on the blockchain that will notify clients */
event FrozenFunds(address target, bool frozen);

/* Initializes contract with initial supply tokens to the creator of the contract */
function BTCx( ) TokenERC20(21000000, "BTCx", "BTCx") public {}

/* Internal transfer, only can be called by this contract */
function _transfer(address _from, address _to, uint _value) internal {
require (_to != 0x0);                               // Prevent transfer to 0x0 address. Use burn() instead
require (balanceOf[_from] >= _value);                // Check if the sender has enough
require (safeAdd(balanceOf[_to], _value) > balanceOf[_to]); // Check for overflows
require(!frozenAccount[_from]);                     // Check if sender is frozen
require(!frozenAccount[_to]);                       // Check if recipient is frozen
balanceOf[_from] =safeSub(balanceOf[_from],_value);                         // Subtract from the sender
balanceOf[_to] =safeAdd(balanceOf[_to],_value);                           // Add the same to the recipient
Transfer(_from, _to, _value);
}

/// @notice Create `mintedAmount` tokens and send it to `target`
/// @param target Address to receive the tokens
/// @param mintedAmount the amount of tokens it will receive
function mintToken(address target, uint256 mintedAmount) onlyOwner public {
balanceOf[target] =safeAdd(balanceOf[target],mintedAmount);
totalSupply =safeAdd(totalSupply,mintedAmount);
Transfer(0, this, mintedAmount);
Transfer(this, target, mintedAmount);
}

/// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
/// @param target Address to be frozen
/// @param freeze either to freeze it or not
function freezeAccount(address target, bool freeze) onlyOwner public {
frozenAccount[target] = freeze;
FrozenFunds(target, freeze);
}



}