pragma solidity ^0.4.16;

/**
 * Math operations with safety checks
 */

contract owned {
    address public owner;

    constructor() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) onlyOwner public {
        owner = newOwner;
    }
}

contract SafeMath {
    function safeMul(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a * b;
        require(a == 0 || c / a == b);
        return c;
    }

    function safeDiv(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0);
        uint256 c = a / b;
        require(a == b * c + a % b);
        return c;
    }

    function safeSub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        return a - b;
    }

    function safeAdd(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c>=a && c>=b);
        return c;
    }
}

contract CollectionToken is owned, SafeMath {
    string public name;
    string public symbol;
    uint8 public decimals;
    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);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    constructor() public {
        totalSupply = 21*10**24; // Update total supply
        
        balanceOf[msg.sender] = totalSupply;              // Give the creator all initial tokens
        name = "Nuts Coin";                                   // Set the name for display purposes
        symbol = "NC";                               // Set the symbol for display purposes
        decimals = 18;                            // Amount of decimals 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(balanceOf[_to] + _value > balanceOf[_to]);
        // Save this for an assertion in the future
        uint previousBalances = balanceOf[_from] + balanceOf[_to];
        // Subtract from the sender
        balanceOf[_from] -= _value;
        // Add the same to the recipient
        balanceOf[_to] += _value;
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }


        /* Send coins */
    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender,_to,_value);
        emit 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]==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(_value <= allowance[_from][msg.sender]);  // Check allowance
        allowance[_from][msg.sender] = SafeMath.safeSub(allowance[_from][msg.sender], _value);
        _transfer(_from, _to, _value);
        emit Transfer(_from, _to, _value);
        return true;
    }

}