pragma solidity ^0.4.24;

library SafeMath {
    
function mul(uint256 _a, uint256 _b) internal pure returns (uint256) {

    if (_a == 0) {
    return 0;
}

    uint256 c = _a * _b;
    require(c / _a == _b);
    return c;
}

function div(uint256 _a, uint256 _b) internal pure returns (uint256) {
    require(_b > 0);
    uint256 c = _a / _b;
    return c;

}

function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {

    require(_b <= _a);
    return _a - _b;
}

function add(uint256 _a, uint256 _b) internal pure returns (uint256) {

    uint256 c = _a + _b;
    require(c >= _a);
    return c;

}

function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0);
    return a % b;
    }
}

contract Ownable {
address public owner;
address public newOwner;
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

constructor() public {
    owner = msg.sender;
    newOwner = address(0);
}

modifier onlyOwner() {
    require(msg.sender == owner);
    _;
}

modifier onlyNewOwner() {
    require(msg.sender != address(0));
    require(msg.sender == newOwner);
    _;
}

function transferOwnership(address _newOwner) public onlyOwner {
    require(_newOwner != address(0));
    newOwner = _newOwner;
}

function acceptOwnership() public onlyNewOwner {
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
    }
}

contract ERC20 {

    function totalSupply() public view returns (uint256);
    function balanceOf(address who) public view returns (uint256);
    function allowance(address owner, address spender) public view returns (uint256);
    function transfer(address to, uint256 value) public returns (bool);
    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);
    event Transfer(address indexed from, address indexed to, uint256 value);
}

interface TokenRecipient {
    function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external;
}

contract CouponBay is ERC20, Ownable {
    
    using SafeMath for uint256;

    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 internal initialSupply;
    uint256 internal totalSupply_;
    mapping(address => uint256) internal balances;
    mapping(address => bool) public frozen;
    mapping(address => mapping(address => uint256)) internal allowed;

    event Burn(address indexed owner, uint256 value);
    event Freeze(address indexed holder);
    event Unfreeze(address indexed holder);

    modifier notFrozen(address _holder) {
    require(!frozen[_holder]);
    _;
}

constructor() public {
    name = "CouponBay";
    symbol = "CUP";
    decimals = 18;
    initialSupply = 1000000000;
    totalSupply_ = initialSupply * 10 ** uint(decimals);
    balances[owner] = totalSupply_;
    emit Transfer(address(0), owner, totalSupply_);
}

function () public payable {
    revert();
}
   
function totalSupply() public view returns (uint256) {
    return totalSupply_;
}

function _transfer(address _from, address _to, uint _value) internal {

    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);
}
 
function transfer(address _to, uint256 _value) public notFrozen(msg.sender) returns (bool) {

    require(_to != address(0));
    require(_value <= balances[msg.sender]);
    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _to, _value);
    
    return true;
}

function balanceOf(address _holder) public view returns (uint256 balance) {
    return balances[_holder];
}
     
function transferFrom(address _from, address _to, uint256 _value) public notFrozen(_from) returns (bool) {

    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);
    _transfer(_from, _to, _value);
    
    return true;
}

function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    
    return true;
}

function allowance(address _holder, address _spender) public view returns (uint256) {
    return allowed[_holder][_spender];

}

function freezeAccount(address _holder) public onlyOwner returns (bool) {

    require(!frozen[_holder]);
    frozen[_holder] = true;
    emit Freeze(_holder);
    
    return true;
}

function unfreezeAccount(address _holder) public onlyOwner returns (bool) {

    require(frozen[_holder]);
    frozen[_holder] = false;
    emit Unfreeze(_holder);
    
    return true;
}

function burn(uint256 _value) public onlyOwner returns (bool) {
    
    require(_value <= balances[msg.sender]);
    address burner = msg.sender;
    balances[burner] = balances[burner].sub(_value);
    totalSupply_ = totalSupply_.sub(_value);
    emit Burn(burner, _value);

    return true;
}

function isContract(address addr) internal view returns (bool) {
    
    uint size;
    assembly{size := extcodesize(addr)}
    
    return size > 0;
    }
}
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