pragma solidity ^0.4.18;

/**
 * Math operations with safety checks
 */
contract SafeMath {
    
  function safeMul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b);
    return c;
  }

  function safeDiv(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b > 0);
    uint256 c = a / b;
    assert(a == b * c + a % b);
    return c;
  }

  function safeSub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function safeAdd(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c>=a && c>=b);
    return c;
  }
  
}
contract QYQ is SafeMath{
    string public name;
    string public symbol;
    uint8 public decimals = 8;
    uint256 public totalSupply;
	address public owner;

    /* This creates an array with all balances */
    mapping (address => uint256) public balanceOf;
	mapping (address => uint256) public freezeOf;
    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);
	
	/* This notifies clients about the amount frozen */
    event Freeze(address indexed from, uint256 value);
	
	/* This notifies clients about the amount unfrozen */
    event Unfreeze(address indexed from, uint256 value);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    function QYQ(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol,
        address holder)  public{
        totalSupply = initialSupply * 10 ** uint256(decimals); // Update total supply
        balanceOf[holder] = totalSupply;                       // Give the creator all initial tokens
        name = tokenName;                                      // Set the name for display purposes
        symbol = tokenSymbol;                                  // Set the symbol for display purposes
		owner = holder;
    }

    /* Send coins */
    function transfer(address _to, uint256 _value) public{
        require(_to != 0x0);  // Prevent transfer to 0x0 address. Use burn() instead
		require(_value > 0); 
        require(balanceOf[msg.sender] >= _value);           // Check if the sender has enough
        require(balanceOf[_to] + _value >= balanceOf[_to]); // Check for overflows
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                     // Subtract from the sender
        balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to], _value);                            // Add the same to the recipient
        Transfer(msg.sender, _to, _value);                   // Notify anyone listening that this transfer took place
    }

    /* Allow another contract to spend some tokens in your behalf */
    function approve(address _spender, uint256 _value) public
        returns (bool success) {
		require(_value > 0); 
        allowance[msg.sender][_spender] = _value;
        return true;
    }
       
    /* A contract attempts to get the coins */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_to != 0x0);                                // Prevent transfer to 0x0 address. Use burn() instead
		require(_value > 0); 
        require(balanceOf[_from] >= _value);                 // Check if the sender has enough
        require(balanceOf[_to] + _value >= balanceOf[_to]);  // Check for overflows
        require(_value <= allowance[_from][msg.sender]);     // Check allowance
        balanceOf[_from] = SafeMath.safeSub(balanceOf[_from], _value);                           // Subtract from the sender
        balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to], _value);                             // Add the same to the recipient
        allowance[_from][msg.sender] = SafeMath.safeSub(allowance[_from][msg.sender], _value);
        Transfer(_from, _to, _value);
        return true;
    }

    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);            // Check if the sender has enough
		require(_value > 0); 
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                      // Subtract from the sender
        totalSupply = SafeMath.safeSub(totalSupply,_value);                                // Updates totalSupply
        Burn(msg.sender, _value);
        return true;
    }
	
	function freeze(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);            // Check if the sender has enough
		require(_value > 0); 
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                      // Subtract from the sender
        freezeOf[msg.sender] = SafeMath.safeAdd(freezeOf[msg.sender], _value);                                // Updates totalSupply
        Freeze(msg.sender, _value);
        return true;
    }
	
	function unfreeze(uint256 _value) public returns (bool success) {
        require(freezeOf[msg.sender] >= _value);            // Check if the sender has enough
		require(_value > 0); 
        freezeOf[msg.sender] = SafeMath.safeSub(freezeOf[msg.sender], _value);                      // Subtract from the sender
		balanceOf[msg.sender] = SafeMath.safeAdd(balanceOf[msg.sender], _value);
        Unfreeze(msg.sender, _value);
        return true;
    }

}