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1_Storage.sol

pragma solidity >=0.4.22 <0.7.0;

/**
 * @title Storage
 * @dev Store & retrieve value in a variable
 */
contract Storage {

    uint256 number;

    /**
     * @dev Store value in variable
     * @param num value to store
     */
    function store(uint256 num) public {
        number = num;
    }

    /**
     * @dev Return value 
     * @return value of 'number'
     */
    function retrieve() public view returns (uint256){
        return number;
    }
}

2_Owner.sol

pragma solidity >=0.4.22 <0.7.0;

/**
 * @title Owner
 * @dev Set & change owner
 */
contract Owner {

    address private owner;
    
    // event for EVM logging
    event OwnerSet(address indexed oldOwner, address indexed newOwner);
    
    // modifier to check if caller is owner
    modifier isOwner() {
        // If the first argument of 'require' evaluates to 'false', execution terminates and all
        // changes to the state and to Ether balances are reverted.
        // This used to consume all gas in old EVM versions, but not anymore.
        // It is often a good idea to use 'require' to check if functions are called correctly.
        // As a second argument, you can also provide an explanation about what went wrong.
        require(msg.sender == owner, "Caller is not owner");
        _;
    }
    
    /**
     * @dev Set contract deployer as owner
     */
    constructor() public {
        owner = msg.sender; // 'msg.sender' is sender of current call, contract deployer for a constructor
        emit OwnerSet(address(0), owner);
    }

    /**
     * @dev Change owner
     * @param newOwner address of new owner
     */
    function changeOwner(address newOwner) public isOwner {
        emit OwnerSet(owner, newOwner);
        owner = newOwner;
    }

    /**
     * @dev Return owner address 
     * @return address of owner
     */
    function getOwner() external view returns (address) {
        return owner;
    }
}

3_Ballot.sol

pragma solidity >=0.4.22 <0.7.0;

/** 
 * @title Ballot
 * @dev Implements voting process along with vote delegation
 */
contract Ballot {
   
    struct Voter {
        uint weight; // weight is accumulated by delegation
        bool voted;  // if true, that person already voted
        address delegate; // person delegated to
        uint vote;   // index of the voted proposal
    }

    struct Proposal {
        // If you can limit the length to a certain number of bytes, 
        // always use one of bytes1 to bytes32 because they are much cheaper
        bytes32 name;   // short name (up to 32 bytes)
        uint voteCount; // number of accumulated votes
    }

    address public chairperson;

    mapping(address => Voter) public voters;

    Proposal[] public proposals;

    /** 
     * @dev Create a new ballot to choose one of 'proposalNames'.
     * @param proposalNames names of proposals
     */
    constructor(bytes32[] memory proposalNames) public {
        chairperson = msg.sender;
        voters[chairperson].weight = 1;

        for (uint i = 0; i < proposalNames.length; i++) {
            // 'Proposal({...})' creates a temporary
            // Proposal object and 'proposals.push(...)'
            // appends it to the end of 'proposals'.
            proposals.push(Proposal({
                name: proposalNames[i],
                voteCount: 0
            }));
        }
    }
    
    /** 
     * @dev Give 'voter' the right to vote on this ballot. May only be called by 'chairperson'.
     * @param voter address of voter
     */
    function giveRightToVote(address voter) public {
        require(
            msg.sender == chairperson,
            "Only chairperson can give right to vote."
        );
        require(
            !voters[voter].voted,
            "The voter already voted."
        );
        require(voters[voter].weight == 0);
        voters[voter].weight = 1;
    }

    /**
     * @dev Delegate your vote to the voter 'to'.
     * @param to address to which vote is delegated
     */
    function delegate(address to) public {
        Voter storage sender = voters[msg.sender];
        require(!sender.voted, "You already voted.");
        require(to != msg.sender, "Self-delegation is disallowed.");

        while (voters[to].delegate != address(0)) {
            to = voters[to].delegate;

            // We found a loop in the delegation, not allowed.
            require(to != msg.sender, "Found loop in delegation.");
        }
        sender.voted = true;
        sender.delegate = to;
        Voter storage delegate_ = voters[to];
        if (delegate_.voted) {
            // If the delegate already voted,
            // directly add to the number of votes
            proposals[delegate_.vote].voteCount += sender.weight;
        } else {
            // If the delegate did not vote yet,
            // add to her weight.
            delegate_.weight += sender.weight;
        }
    }

    /**
     * @dev Give your vote (including votes delegated to you) to proposal 'proposals[proposal].name'.
     * @param proposal index of proposal in the proposals array
     */
    function vote(uint proposal) public {
        Voter storage sender = voters[msg.sender];
        require(sender.weight != 0, "Has no right to vote");
        require(!sender.voted, "Already voted.");
        sender.voted = true;
        sender.vote = proposal;

        // If 'proposal' is out of the range of the array,
        // this will throw automatically and revert all
        // changes.
        proposals[proposal].voteCount += sender.weight;
    }

    /** 
     * @dev Computes the winning proposal taking all previous votes into account.
     * @return winningProposal_ index of winning proposal in the proposals array
     */
    function winningProposal() public view
            returns (uint winningProposal_)
    {
        uint winningVoteCount = 0;
        for (uint p = 0; p < proposals.length; p++) {
            if (proposals[p].voteCount > winningVoteCount) {
                winningVoteCount = proposals[p].voteCount;
                winningProposal_ = p;
            }
        }
    }

    /** 
     * @dev Calls winningProposal() function to get the index of the winner contained in the proposals array and then
     * @return winnerName_ the name of the winner
     */
    function winnerName() public view
            returns (bytes32 winnerName_)
    {
        winnerName_ = proposals[winningProposal()].name;
    }
}

Allowance.sol

pragma solidity ^0.6.0;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol";

contract Allowance is Ownable {
    using SafeMath for uint;
    
    event allowanceChanged(address indexed _from, address indexed _to, uint _oldAmount, uint _newAmount);
    
    mapping(address => uint) public allowance;
    
    function isOwner() internal view returns(bool) {
         return owner() == msg.sender;
    }
    
    modifier OwnerorUser(address _to) {
        require(isOwner() || msg.sender == _to, "You are not allowed");
        _;
    }
    
    function setAllowance(address _who, uint _amount) public onlyOwner {
        emit allowanceChanged(msg.sender,_who,allowance[_who],_amount);
        allowance[_who] = _amount;
    }
    
    function reduceAllowance(address _who, uint _amount) internal OwnerorUser(_who) {
        emit allowanceChanged(msg.sender,_who,allowance[_who],allowance[_who].sub(_amount));
        allowance[_who] = allowance[_who].sub(_amount);
    }
    
}

auction.sol

pragma solidity > 0.6.0;

contract SimpleAuction {
    address payable public beneficiary;
    uint public auctionEnd;

    // Current state of the auction.
    address public highestBidder;
    uint public highestBid;

    mapping(address => uint) pendingReturns;

    bool ended;

    event HighestBidIncreased(address bidder, uint amount);
    event AuctionEnded(address winner, uint amount);


    constructor(
        uint _biddingTime,
        address payable _beneficiary
    ) public {
        beneficiary = _beneficiary;
        auctionEnd = block.timestamp + _biddingTime;
    }

    
    function bid() public payable {
        // No arguments are necessary, all
        // information is already part of
        // the transaction. The keyword payable
        // is required for the function to
        // be able to receive Ether.

        // Revert the call if the bidding
        // period is over.
        require(
            block.timestamp <= auctionEnd,
            "Auction already ended."
        );

        // If the bid is not higher, send the
        // money back.
        require(
            msg.value > highestBid,
            "There already is a higher bid."
        );

        if (highestBid != 0) {
            
            pendingReturns[highestBidder] += highestBid;
        }
        highestBidder = msg.sender;
        highestBid = msg.value;
        emit HighestBidIncreased(msg.sender, msg.value);
    }

    /// Withdraw a bid that was overbid.
    function withdraw() public returns (bool) {
        uint amount = pendingReturns[msg.sender];
        if (amount > 0) {
            
            pendingReturns[msg.sender] = 0;

            if (!msg.sender.send(amount)) {
                // No need to call throw here, just reset the amount owing
                pendingReturns[msg.sender] = amount;
                return false;
            }
        }
        return true;
    }

    /// End the auction and send the highest bid
    /// to the beneficiary.
    function auctionFinished() public {
        
        // 1. Conditions
        require(block.timestamp >= auctionEnd, "Auction not yet ended.");
        require(!ended, "auctionEnd has already been called.");

        // 2. Effects
        ended = true;
        emit AuctionEnded(highestBidder, highestBid);

        // 3. Interaction
        beneficiary.transfer(highestBid);
    }
}

checkContract.sol

pragma solidity ^0.6.0;

contract checkContract {
    address public address1 = 0x2EB8291d3a6b72cf55B000610B6485b68783D330;
    address public address2 = 0x56123d3026134107A4241ce6cD8B5aABdBd0b1F6;
    address public addressToken = 0xa2c90542Cb9E2fD85d69fe658fD92168156E7F17;
    
}

collectible.sol

pragma solidity ^0.4.24;

// File: openzeppelin-solidity/contracts/introspection/ERC165.sol

/**
 * @title ERC165
 * @dev https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md
 */
interface ERC165 {

  /**
   * @notice Query if a contract implements an interface
   * @param _interfaceId The interface identifier, as specified in ERC-165
   * @dev Interface identification is specified in ERC-165. This function
   * uses less than 30,000 gas.
   */
  function supportsInterface(bytes4 _interfaceId)
    external
    view
    returns (bool);
}

// File: openzeppelin-solidity/contracts/token/ERC721/ERC721Basic.sol

/**
 * @title ERC721 Non-Fungible Token Standard basic interface
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721Basic is ERC165 {

  bytes4 internal constant InterfaceId_ERC721 = 0x80ac58cd;
  /*
   * 0x80ac58cd ===
   *   bytes4(keccak256('balanceOf(address)')) ^
   *   bytes4(keccak256('ownerOf(uint256)')) ^
   *   bytes4(keccak256('approve(address,uint256)')) ^
   *   bytes4(keccak256('getApproved(uint256)')) ^
   *   bytes4(keccak256('setApprovalForAll(address,bool)')) ^
   *   bytes4(keccak256('isApprovedForAll(address,address)')) ^
   *   bytes4(keccak256('transferFrom(address,address,uint256)')) ^
   *   bytes4(keccak256('safeTransferFrom(address,address,uint256)')) ^
   *   bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)'))
   */

  bytes4 internal constant InterfaceId_ERC721Exists = 0x4f558e79;
  /*
   * 0x4f558e79 ===
   *   bytes4(keccak256('exists(uint256)'))
   */

  bytes4 internal constant InterfaceId_ERC721Enumerable = 0x780e9d63;
  /**
   * 0x780e9d63 ===
   *   bytes4(keccak256('totalSupply()')) ^
   *   bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) ^
   *   bytes4(keccak256('tokenByIndex(uint256)'))
   */

  bytes4 internal constant InterfaceId_ERC721Metadata = 0x5b5e139f;
  /**
   * 0x5b5e139f ===
   *   bytes4(keccak256('name()')) ^
   *   bytes4(keccak256('symbol()')) ^
   *   bytes4(keccak256('tokenURI(uint256)'))
   */

  event Transfer(
    address indexed _from,
    address indexed _to,
    uint256 indexed _tokenId
  );
  event Approval(
    address indexed _owner,
    address indexed _approved,
    uint256 indexed _tokenId
  );
  event ApprovalForAll(
    address indexed _owner,
    address indexed _operator,
    bool _approved
  );

  function balanceOf(address _owner) public view returns (uint256 _balance);
  function ownerOf(uint256 _tokenId) public view returns (address _owner);
  function exists(uint256 _tokenId) public view returns (bool _exists);

  function approve(address _to, uint256 _tokenId) public;
  function getApproved(uint256 _tokenId)
    public view returns (address _operator);

  function setApprovalForAll(address _operator, bool _approved) public;
  function isApprovedForAll(address _owner, address _operator)
    public view returns (bool);

  function transferFrom(address _from, address _to, uint256 _tokenId) public;
  function safeTransferFrom(address _from, address _to, uint256 _tokenId)
    public;

  function safeTransferFrom(
    address _from,
    address _to,
    uint256 _tokenId,
    bytes _data
  )
    public;
}

// File: openzeppelin-solidity/contracts/token/ERC721/ERC721.sol

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721Enumerable is ERC721Basic {
  function totalSupply() public view returns (uint256);
  function tokenOfOwnerByIndex(
    address _owner,
    uint256 _index
  )
    public
    view
    returns (uint256 _tokenId);

  function tokenByIndex(uint256 _index) public view returns (uint256);
}


/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721Metadata is ERC721Basic {
  function name() external view returns (string _name);
  function symbol() external view returns (string _symbol);
  function tokenURI(uint256 _tokenId) public view returns (string);
}


/**
 * @title ERC-721 Non-Fungible Token Standard, full implementation interface
 * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721 is ERC721Basic, ERC721Enumerable, ERC721Metadata {
}

// File: openzeppelin-solidity/contracts/token/ERC721/ERC721Receiver.sol

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
contract ERC721Receiver {
  /**
   * @dev Magic value to be returned upon successful reception of an NFT
   *  Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`,
   *  which can be also obtained as `ERC721Receiver(0).onERC721Received.selector`
   */
  bytes4 internal constant ERC721_RECEIVED = 0x150b7a02;

  /**
   * @notice Handle the receipt of an NFT
   * @dev The ERC721 smart contract calls this function on the recipient
   * after a `safetransfer`. This function MAY throw to revert and reject the
   * transfer. Return of other than the magic value MUST result in the
   * transaction being reverted.
   * Note: the contract address is always the message sender.
   * @param _operator The address which called `safeTransferFrom` function
   * @param _from The address which previously owned the token
   * @param _tokenId The NFT identifier which is being transferred
   * @param _data Additional data with no specified format
   * @return `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
   */
  function onERC721Received(
    address _operator,
    address _from,
    uint256 _tokenId,
    bytes _data
  )
    public
    returns(bytes4);
}

// File: openzeppelin-solidity/contracts/math/SafeMath.sol

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  function mul(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
    // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (_a == 0) {
      return 0;
    }

    c = _a * _b;
    assert(c / _a == _b);
    return c;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  function div(uint256 _a, uint256 _b) internal pure returns (uint256) {
    // assert(_b > 0); // Solidity automatically throws when dividing by 0
    // uint256 c = _a / _b;
    // assert(_a == _b * c + _a % _b); // There is no case in which this doesn't hold
    return _a / _b;
  }

  /**
  * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
    assert(_b <= _a);
    return _a - _b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
    c = _a + _b;
    assert(c >= _a);
    return c;
  }
}

// File: openzeppelin-solidity/contracts/AddressUtils.sol

/**
 * Utility library of inline functions on addresses
 */
library AddressUtils {

  /**
   * Returns whether the target address is a contract
   * @dev This function will return false if invoked during the constructor of a contract,
   * as the code is not actually created until after the constructor finishes.
   * @param _addr address to check
   * @return whether the target address is a contract
   */
  function isContract(address _addr) internal view returns (bool) {
    uint256 size;
    // XXX Currently there is no better way to check if there is a contract in an address
    // than to check the size of the code at that address.
    // See https://ethereum.stackexchange.com/a/14016/36603
    // for more details about how this works.
    // TODO Check this again before the Serenity release, because all addresses will be
    // contracts then.
    // solium-disable-next-line security/no-inline-assembly
    assembly { size := extcodesize(_addr) }
    return size > 0;
  }

}

// File: openzeppelin-solidity/contracts/introspection/SupportsInterfaceWithLookup.sol

/**
 * @title SupportsInterfaceWithLookup
 * @author Matt Condon (@shrugs)
 * @dev Implements ERC165 using a lookup table.
 */
contract SupportsInterfaceWithLookup is ERC165 {

  bytes4 public constant InterfaceId_ERC165 = 0x01ffc9a7;
  /**
   * 0x01ffc9a7 ===
   *   bytes4(keccak256('supportsInterface(bytes4)'))
   */

  /**
   * @dev a mapping of interface id to whether or not it's supported
   */
  mapping(bytes4 => bool) internal supportedInterfaces;

  /**
   * @dev A contract implementing SupportsInterfaceWithLookup
   * implement ERC165 itself
   */
  constructor()
    public
  {
    _registerInterface(InterfaceId_ERC165);
  }

  /**
   * @dev implement supportsInterface(bytes4) using a lookup table
   */
  function supportsInterface(bytes4 _interfaceId)
    external
    view
    returns (bool)
  {
    return supportedInterfaces[_interfaceId];
  }

  /**
   * @dev private method for registering an interface
   */
  function _registerInterface(bytes4 _interfaceId)
    internal
  {
    require(_interfaceId != 0xffffffff);
    supportedInterfaces[_interfaceId] = true;
  }
}

// File: openzeppelin-solidity/contracts/token/ERC721/ERC721BasicToken.sol

/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721BasicToken is SupportsInterfaceWithLookup, ERC721Basic {

  using SafeMath for uint256;
  using AddressUtils for address;

  // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
  // which can be also obtained as `ERC721Receiver(0).onERC721Received.selector`
  bytes4 private constant ERC721_RECEIVED = 0x150b7a02;

  // Mapping from token ID to owner
  mapping (uint256 => address) internal tokenOwner;

  // Mapping from token ID to approved address
  mapping (uint256 => address) internal tokenApprovals;

  // Mapping from owner to number of owned token
  mapping (address => uint256) internal ownedTokensCount;

  // Mapping from owner to operator approvals
  mapping (address => mapping (address => bool)) internal operatorApprovals;

  constructor()
    public
  {
    // register the supported interfaces to conform to ERC721 via ERC165
    _registerInterface(InterfaceId_ERC721);
    _registerInterface(InterfaceId_ERC721Exists);
  }

  /**
   * @dev Gets the balance of the specified address
   * @param _owner address to query the balance of
   * @return uint256 representing the amount owned by the passed address
   */
  function balanceOf(address _owner) public view returns (uint256) {
    require(_owner != address(0));
    return ownedTokensCount[_owner];
  }

  /**
   * @dev Gets the owner of the specified token ID
   * @param _tokenId uint256 ID of the token to query the owner of
   * @return owner address currently marked as the owner of the given token ID
   */
  function ownerOf(uint256 _tokenId) public view returns (address) {
    address owner = tokenOwner[_tokenId];
    require(owner != address(0));
    return owner;
  }

  /**
   * @dev Returns whether the specified token exists
   * @param _tokenId uint256 ID of the token to query the existence of
   * @return whether the token exists
   */
  function exists(uint256 _tokenId) public view returns (bool) {
    address owner = tokenOwner[_tokenId];
    return owner != address(0);
  }

  /**
   * @dev Approves another address to transfer the given token ID
   * The zero address indicates there is no approved address.
   * There can only be one approved address per token at a given time.
   * Can only be called by the token owner or an approved operator.
   * @param _to address to be approved for the given token ID
   * @param _tokenId uint256 ID of the token to be approved
   */
  function approve(address _to, uint256 _tokenId) public {
    address owner = ownerOf(_tokenId);
    require(_to != owner);
    require(msg.sender == owner || isApprovedForAll(owner, msg.sender));

    tokenApprovals[_tokenId] = _to;
    emit Approval(owner, _to, _tokenId);
  }

  /**
   * @dev Gets the approved address for a token ID, or zero if no address set
   * @param _tokenId uint256 ID of the token to query the approval of
   * @return address currently approved for the given token ID
   */
  function getApproved(uint256 _tokenId) public view returns (address) {
    return tokenApprovals[_tokenId];
  }

  /**
   * @dev Sets or unsets the approval of a given operator
   * An operator is allowed to transfer all tokens of the sender on their behalf
   * @param _to operator address to set the approval
   * @param _approved representing the status of the approval to be set
   */
  function setApprovalForAll(address _to, bool _approved) public {
    require(_to != msg.sender);
    operatorApprovals[msg.sender][_to] = _approved;
    emit ApprovalForAll(msg.sender, _to, _approved);
  }

  /**
   * @dev Tells whether an operator is approved by a given owner
   * @param _owner owner address which you want to query the approval of
   * @param _operator operator address which you want to query the approval of
   * @return bool whether the given operator is approved by the given owner
   */
  function isApprovedForAll(
    address _owner,
    address _operator
  )
    public
    view
    returns (bool)
  {
    return operatorApprovals[_owner][_operator];
  }

  /**
   * @dev Transfers the ownership of a given token ID to another address
   * Usage of this method is discouraged, use `safeTransferFrom` whenever possible
   * Requires the msg sender to be the owner, approved, or operator
   * @param _from current owner of the token
   * @param _to address to receive the ownership of the given token ID
   * @param _tokenId uint256 ID of the token to be transferred
  */
  function transferFrom(
    address _from,
    address _to,
    uint256 _tokenId
  )
    public
  {
    require(isApprovedOrOwner(msg.sender, _tokenId));
    require(_from != address(0));
    require(_to != address(0));

    clearApproval(_from, _tokenId);
    removeTokenFrom(_from, _tokenId);
    addTokenTo(_to, _tokenId);

    emit Transfer(_from, _to, _tokenId);
  }

  /**
   * @dev Safely transfers the ownership of a given token ID to another address
   * If the target address is a contract, it must implement `onERC721Received`,
   * which is called upon a safe transfer, and return the magic value
   * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
   * the transfer is reverted.
   *
   * Requires the msg sender to be the owner, approved, or operator
   * @param _from current owner of the token
   * @param _to address to receive the ownership of the given token ID
   * @param _tokenId uint256 ID of the token to be transferred
  */
  function safeTransferFrom(
    address _from,
    address _to,
    uint256 _tokenId
  )
    public
  {
    // solium-disable-next-line arg-overflow
    safeTransferFrom(_from, _to, _tokenId, "");
  }

  /**
   * @dev Safely transfers the ownership of a given token ID to another address
   * If the target address is a contract, it must implement `onERC721Received`,
   * which is called upon a safe transfer, and return the magic value
   * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
   * the transfer is reverted.
   * Requires the msg sender to be the owner, approved, or operator
   * @param _from current owner of the token
   * @param _to address to receive the ownership of the given token ID
   * @param _tokenId uint256 ID of the token to be transferred
   * @param _data bytes data to send along with a safe transfer check
   */
  function safeTransferFrom(
    address _from,
    address _to,
    uint256 _tokenId,
    bytes _data
  )
    public
  {
    transferFrom(_from, _to, _tokenId);
    // solium-disable-next-line arg-overflow
    require(checkAndCallSafeTransfer(_from, _to, _tokenId, _data));
  }

  /**
   * @dev Returns whether the given spender can transfer a given token ID
   * @param _spender address of the spender to query
   * @param _tokenId uint256 ID of the token to be transferred
   * @return bool whether the msg.sender is approved for the given token ID,
   *  is an operator of the owner, or is the owner of the token
   */
  function isApprovedOrOwner(
    address _spender,
    uint256 _tokenId
  )
    internal
    view
    returns (bool)
  {
    address owner = ownerOf(_tokenId);
    // Disable solium check because of
    // https://github.com/duaraghav8/Solium/issues/175
    // solium-disable-next-line operator-whitespace
    return (
      _spender == owner ||
      getApproved(_tokenId) == _spender ||
      isApprovedForAll(owner, _spender)
    );
  }

  /**
   * @dev Internal function to mint a new token
   * Reverts if the given token ID already exists
   * @param _to The address that will own the minted token
   * @param _tokenId uint256 ID of the token to be minted by the msg.sender
   */
  function _mint(address _to, uint256 _tokenId) internal {
    require(_to != address(0));
    addTokenTo(_to, _tokenId);
    emit Transfer(address(0), _to, _tokenId);
  }

  /**
   * @dev Internal function to burn a specific token
   * Reverts if the token does not exist
   * @param _tokenId uint256 ID of the token being burned by the msg.sender
   */
  function _burn(address _owner, uint256 _tokenId) internal {
    clearApproval(_owner, _tokenId);
    removeTokenFrom(_owner, _tokenId);
    emit Transfer(_owner, address(0), _tokenId);
  }

  /**
   * @dev Internal function to clear current approval of a given token ID
   * Reverts if the given address is not indeed the owner of the token
   * @param _owner owner of the token
   * @param _tokenId uint256 ID of the token to be transferred
   */
  function clearApproval(address _owner, uint256 _tokenId) internal {
    require(ownerOf(_tokenId) == _owner);
    if (tokenApprovals[_tokenId] != address(0)) {
      tokenApprovals[_tokenId] = address(0);
    }
  }

  /**
   * @dev Internal function to add a token ID to the list of a given address
   * @param _to address representing the new owner of the given token ID
   * @param _tokenId uint256 ID of the token to be added to the tokens list of the given address
   */
  function addTokenTo(address _to, uint256 _tokenId) internal {
    require(tokenOwner[_tokenId] == address(0));
    tokenOwner[_tokenId] = _to;
    ownedTokensCount[_to] = ownedTokensCount[_to].add(1);
  }

  /**
   * @dev Internal function to remove a token ID from the list of a given address
   * @param _from address representing the previous owner of the given token ID
   * @param _tokenId uint256 ID of the token to be removed from the tokens list of the given address
   */
  function removeTokenFrom(address _from, uint256 _tokenId) internal {
    require(ownerOf(_tokenId) == _from);
    ownedTokensCount[_from] = ownedTokensCount[_from].sub(1);
    tokenOwner[_tokenId] = address(0);
  }

  /**
   * @dev Internal function to invoke `onERC721Received` on a target address
   * The call is not executed if the target address is not a contract
   * @param _from address representing the previous owner of the given token ID
   * @param _to target address that will receive the tokens
   * @param _tokenId uint256 ID of the token to be transferred
   * @param _data bytes optional data to send along with the call
   * @return whether the call correctly returned the expected magic value
   */
  function checkAndCallSafeTransfer(
    address _from,
    address _to,
    uint256 _tokenId,
    bytes _data
  )
    internal
    returns (bool)
  {
    if (!_to.isContract()) {
      return true;
    }
    bytes4 retval = ERC721Receiver(_to).onERC721Received(
      msg.sender, _from, _tokenId, _data);
    return (retval == ERC721_RECEIVED);
  }
}

// File: openzeppelin-solidity/contracts/token/ERC721/ERC721Token.sol

/**
 * @title Full ERC721 Token
 * This implementation includes all the required and some optional functionality of the ERC721 standard
 * Moreover, it includes approve all functionality using operator terminology
 * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
 */
contract ERC721Token is SupportsInterfaceWithLookup, ERC721BasicToken, ERC721 {

  // Token name
  string internal name_;

  // Token symbol
  string internal symbol_;

  // Mapping from owner to list of owned token IDs
  mapping(address => uint256[]) internal ownedTokens;

  // Mapping from token ID to index of the owner tokens list
  mapping(uint256 => uint256) internal ownedTokensIndex;

  // Array with all token ids, used for enumeration
  uint256[] internal allTokens;

  // Mapping from token id to position in the allTokens array
  mapping(uint256 => uint256) internal allTokensIndex;

  // Optional mapping for token URIs
  mapping(uint256 => string) internal tokenURIs;

  /**
   * @dev Constructor function
   */
  constructor(string _name, string _symbol) public {
    name_ = _name;
    symbol_ = _symbol;

    // register the supported interfaces to conform to ERC721 via ERC165
    _registerInterface(InterfaceId_ERC721Enumerable);
    _registerInterface(InterfaceId_ERC721Metadata);
  }

  /**
   * @dev Gets the token name
   * @return string representing the token name
   */
  function name() external view returns (string) {
    return name_;
  }

  /**
   * @dev Gets the token symbol
   * @return string representing the token symbol
   */
  function symbol() external view returns (string) {
    return symbol_;
  }

  /**
   * @dev Returns an URI for a given token ID
   * Throws if the token ID does not exist. May return an empty string.
   * @param _tokenId uint256 ID of the token to query
   */
  function tokenURI(uint256 _tokenId) public view returns (string) {
    require(exists(_tokenId));
    return tokenURIs[_tokenId];
  }

  /**
   * @dev Gets the token ID at a given index of the tokens list of the requested owner
   * @param _owner address owning the tokens list to be accessed
   * @param _index uint256 representing the index to be accessed of the requested tokens list
   * @return uint256 token ID at the given index of the tokens list owned by the requested address
   */
  function tokenOfOwnerByIndex(
    address _owner,
    uint256 _index
  )
    public
    view
    returns (uint256)
  {
    require(_index < balanceOf(_owner));
    return ownedTokens[_owner][_index];
  }

  /**
   * @dev Gets the total amount of tokens stored by the contract
   * @return uint256 representing the total amount of tokens
   */
  function totalSupply() public view returns (uint256) {
    return allTokens.length;
  }

  /**
   * @dev Gets the token ID at a given index of all the tokens in this contract
   * Reverts if the index is greater or equal to the total number of tokens
   * @param _index uint256 representing the index to be accessed of the tokens list
   * @return uint256 token ID at the given index of the tokens list
   */
  function tokenByIndex(uint256 _index) public view returns (uint256) {
    require(_index < totalSupply());
    return allTokens[_index];
  }

  /**
   * @dev Internal function to set the token URI for a given token
   * Reverts if the token ID does not exist
   * @param _tokenId uint256 ID of the token to set its URI
   * @param _uri string URI to assign
   */
  function _setTokenURI(uint256 _tokenId, string _uri) internal {
    require(exists(_tokenId));
    tokenURIs[_tokenId] = _uri;
  }

  /**
   * @dev Internal function to add a token ID to the list of a given address
   * @param _to address representing the new owner of the given token ID
   * @param _tokenId uint256 ID of the token to be added to the tokens list of the given address
   */
  function addTokenTo(address _to, uint256 _tokenId) internal {
    super.addTokenTo(_to, _tokenId);
    uint256 length = ownedTokens[_to].length;
    ownedTokens[_to].push(_tokenId);
    ownedTokensIndex[_tokenId] = length;
  }

  /**
   * @dev Internal function to remove a token ID from the list of a given address
   * @param _from address representing the previous owner of the given token ID
   * @param _tokenId uint256 ID of the token to be removed from the tokens list of the given address
   */
  function removeTokenFrom(address _from, uint256 _tokenId) internal {
    super.removeTokenFrom(_from, _tokenId);

    // To prevent a gap in the array, we store the last token in the index of the token to delete, and
    // then delete the last slot.
    uint256 tokenIndex = ownedTokensIndex[_tokenId];
    uint256 lastTokenIndex = ownedTokens[_from].length.sub(1);
    uint256 lastToken = ownedTokens[_from][lastTokenIndex];

    ownedTokens[_from][tokenIndex] = lastToken;
    // This also deletes the contents at the last position of the array
    ownedTokens[_from].length--;

    // Note that this will handle single-element arrays. In that case, both tokenIndex and lastTokenIndex are going to
    // be zero. Then we can make sure that we will remove _tokenId from the ownedTokens list since we are first swapping
    // the lastToken to the first position, and then dropping the element placed in the last position of the list

    ownedTokensIndex[_tokenId] = 0;
    ownedTokensIndex[lastToken] = tokenIndex;
  }

  /**
   * @dev Internal function to mint a new token
   * Reverts if the given token ID already exists
   * @param _to address the beneficiary that will own the minted token
   * @param _tokenId uint256 ID of the token to be minted by the msg.sender
   */
  function _mint(address _to, uint256 _tokenId) internal {
    super._mint(_to, _tokenId);

    allTokensIndex[_tokenId] = allTokens.length;
    allTokens.push(_tokenId);
  }

  /**
   * @dev Internal function to burn a specific token
   * Reverts if the token does not exist
   * @param _owner owner of the token to burn
   * @param _tokenId uint256 ID of the token being burned by the msg.sender
   */
  function _burn(address _owner, uint256 _tokenId) internal {
    super._burn(_owner, _tokenId);

    // Clear metadata (if any)
    if (bytes(tokenURIs[_tokenId]).length != 0) {
      delete tokenURIs[_tokenId];
    }

    // Reorg all tokens array
    uint256 tokenIndex = allTokensIndex[_tokenId];
    uint256 lastTokenIndex = allTokens.length.sub(1);
    uint256 lastToken = allTokens[lastTokenIndex];

    allTokens[tokenIndex] = lastToken;
    allTokens[lastTokenIndex] = 0;

    allTokens.length--;
    allTokensIndex[_tokenId] = 0;
    allTokensIndex[lastToken] = tokenIndex;
  }

}

// File: crypto-collectible.sol

pragma solidity^0.4.24;


contract Collectible is ERC721Token {
  constructor() ERC721Token("Collectible", "COL") public {}

  struct Color {
    uint8 red;
    uint8 green;
    uint8 blue;
  }

  Color[] colors;

  function mint() public {
    Color memory _color = Color(uint8(now), uint8(now-1000), uint8(now-5500));
    uint _id = colors.push(_color) - 1;
    _mint(msg.sender, _id);
  }

  function getColorFromId(uint id) public view returns(uint8, uint8, uint8) {
    return (colors[id].red, colors[id].green, colors[id].blue);
  }
}

eventsexample.sol

pragma solidity ^0.5.11;
contract EventExample {
    
     mapping(address => uint) public tokenBalance;
     
     event TokensSent(address _from, address _to, uint _amount);
    
     constructor() public {
         tokenBalance[msg.sender] = 100;
     }
    
     function sendToken(address _to, uint _amount) public returns(bool) {
         require(tokenBalance[msg.sender] >= _amount, "Not enough tokens");
         assert(tokenBalance[_to] + _amount >= tokenBalance[_to]);
         assert(tokenBalance[msg.sender] - _amount <= tokenBalance[msg.sender])
    ;
     tokenBalance[msg.sender] -= _amount;
     tokenBalance[_to] += _amount;
     
     emit TokensSent(msg.sender,_to,_amount);
    
     return true;
    }

}

eventtrigger_lecture.sol

pragma solidity ^0.6.0;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol";

contract Item {
    uint public priceInWei;
    uint publicIndex;
    uint public paid;
    
    ItemManager parentContract;
    
    constructor(ItemManager _parentContract, uint _priceInWei, uint _index) public {
        priceInWei = _priceInWei;
        publicIndex = _index;
        parentContract = _parentContract;
    }
    
    receive() external payable {
        require(paid == 0, "Price is already paid");
        require(priceInWei == msg.value, "Only Full Payments Allowed");
        paid += msg.value;
        (bool success,) = address(parentContract).call{value:msg.value}(abi.encodeWithSignature("triggerPayment(uint256)",publicIndex));
        require(success,"the transaction was unsuccessful");
    }
    
    fallback() external {}
}

contract ItemManager is Ownable {
    
    enum SupplyChainState{created,paid,delivered}
    
    struct S_Item {
        Item item;
        string identifier;
        uint price;
        ItemManager.SupplyChainState state;
    }
    
    uint _itemIndex;
    mapping (uint => S_Item) public items;
    event supplychainStep(uint _itemIndex, uint _step,address _itemAddress);
    
    function isOwner() internal view returns(bool) {
         return owner() == msg.sender;
    }
    
    
    function createItem(string memory _identifier, uint _itemPrice) public onlyOwner {
        Item item = new Item(this,_itemPrice,_itemIndex);
        items[_itemIndex].item = item;
        items[_itemIndex].identifier = _identifier;
        items[_itemIndex].price = _itemPrice;
        items[_itemIndex].state = SupplyChainState.created;
        
        emit supplychainStep(_itemIndex,uint(items[_itemIndex].state),address(item));
        _itemIndex++;
    }
    
    function triggerPayment(uint itemIndex) public payable {
        require(items[itemIndex].price == msg.value,"The price is incorrect.");
        require (items[itemIndex].state == SupplyChainState.created, "Item is not available for sale.");
        
        items[itemIndex].state = SupplyChainState.paid;
        
        emit supplychainStep(itemIndex,uint(items[itemIndex].state),address(items[itemIndex].item));
    }
    
    function triggerDelivery(uint itemIndex) public onlyOwner {
        require (items[itemIndex].state == SupplyChainState.paid, "Item is further in the chain");
        items[itemIndex].state = SupplyChainState.delivered;
        emit supplychainStep(itemIndex,uint(items[itemIndex].state),address(items[itemIndex].item));
    }
}

exceptionexample.sol

pragma solidity > 0.5.13;

contract ExceptionExample {
    mapping (address => uint) public balanceReceived;
    
    function receiveMoney() public payable {
        assert(balanceReceived[msg.sender] + msg.value >= balanceReceived[msg.sender]);
        balanceReceived[msg.sender] += msg.value;
    }
    
    function withdrawMoney(address payable _to, uint _amount) public {
        require(_amount <= balanceReceived[msg.sender],"You don't have enough ether");
        assert(balanceReceived[msg.sender] - _amount <= balanceReceived[msg.sender]);
        
        balanceReceived[msg.sender] -= _amount;
        _to.transfer(_amount);
    }
    
}

functionsexample.sol

pragma solidity > 0.5.13;

contract ExceptionExample {
    mapping (address => uint) public balanceReceived;
    address payable public owner;
    
    constructor() public {
        owner = msg.sender;
    }
    
    function destroyContract() public {
        require(msg.sender == owner);
        selfdestruct(owner);
    }
    
    function getOwner() public view returns (address) {
        return owner;
    }
    
    function receiveMoney() public payable {
        assert(balanceReceived[msg.sender] + msg.value >= balanceReceived[msg.sender]);
        balanceReceived[msg.sender] += msg.value;
    }
    
    function withdrawMoney(address payable _to, uint _amount) public {
        require(_amount <= balanceReceived[msg.sender],"You don't have enough ether");
        assert(balanceReceived[msg.sender] - _amount <= balanceReceived[msg.sender]);
        
        balanceReceived[msg.sender] -= _amount;
        _to.transfer(_amount);
    }
    
    receive () external payable {
        receiveMoney();
    }
}

incone.sol

pragma solidity >0.5.10;

contract incone {
	uint256 private value;

	/// Constructor that initializes the `uint256` value to the given `init_value`.
	constructor (uint256 initvalue) public {
		value = initvalue;
	}

	/// Adds one to a uint
	function inc() public {
		value = value+1;
	}

	/// Simply returns the current value of 'uint256'
	function get() public view returns (uint256) {
		return value;
	}
}

inheritancemodifierexample.sol

pragma solidity > 0.5.13;

import './owned.sol';

contract InheritanceModifierExample is Owned {
    
    mapping (address => uint) public tokenBalance;
    
    uint tokenPrice = 1 ether;
    
    constructor() {
        tokenBalance[owner] = 100;
    }
    
    
    function createNewToken() public onlyOwner {
        tokenBalance[owner]++;
    }
    
    function burnToken() public onlyOwner {
        tokenBalance[owner]--;
    }
    
    function purchaseToken() public payable {
        require(tokenBalance[owner] >= msg.value/tokenPrice, "Not enough Tokens available to purchase");
        tokenBalance[owner] -= msg.value/tokenPrice;
        tokenBalance[msg.sender] += msg.value/tokenPrice;
    }
    
    function sendToken(address payable _to, uint _number) public {
        require(tokenBalance[msg.sender] >= _number, "Not enough Tokens available to send");
        assert(tokenBalance[_to] + _number >= tokenBalance[_to]);
        assert(tokenBalance[msg.sender] >= tokenBalance[msg.sender] - _number);
        tokenBalance[msg.sender] -= _number;
        tokenBalance[_to] += _number;
    }
}

Libraries.sol

pragma solidity ^0.6.0;

import "https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-contracts/master/contracts/math/SafeMath.sol";

contract LibrariesExample {
    
    using SafeMath for uint;

     mapping(address => uint) public tokenBalance;
    
     constructor() public {
         tokenBalance[msg.sender] = 1;
     }
    
     function sendToken(address _to, uint _amount) public returns(bool) {
         tokenBalance[msg.sender] =  tokenBalance[msg.sender].sub(_amount);
         tokenBalance[_to] = tokenBalance[_to].add(_amount);
        
         return true;
     }

}

MappingExample.sol

pragma solidity > 0.5.13;

contract MappingExample {
    mapping(uint256 => bool) public myMapping;
    mapping(address => bool) public myAddress;
    
    function setValue(uint256 _index) public {
        myMapping[_index] = true;
    }
    
    function setAddressMapping() public {
        myAddress[msg.sender] = true;
    }
}

mappingstructexample.sol

pragma solidity > 0.5.13;

contract MappingStructExample {
    struct Payment {
        uint amount;
        uint timestamp;
    }
    
    struct Balance {
        uint totalBalance;
        uint numPayments;
        mapping(uint => Payment) payments;
        
    }
    
    mapping(address => Balance) public balanceReceived;
    
    function sendMoney() public payable {
        balanceReceived[msg.sender].totalBalance += msg.value;
        
        Payment memory payment = Payment(msg.value,now);
        
        balanceReceived[msg.sender].payments[balanceReceived[msg.sender].numPayments] = payment;
        balanceReceived[msg.sender].numPayments += 1;
    }
    
    
    function getBalance() public view returns (uint) {
        return address(this).balance;
    }
    
    function withdrawAllMoney(address payable _to) public {
        uint balanceToSend = balanceReceived[msg.sender].totalBalance;
        balanceReceived[msg.sender].totalBalance = 0;
        _to.transfer(balanceToSend);
    }
    
    function withdrawMoney(address payable _to, uint _amount) public {
        require(balanceReceived[msg.sender].totalBalance >= _amount, "Not enough funds to excute transaction");
        balanceReceived[msg.sender].totalBalance -= _amount;
        _to.transfer(_amount);
    }
}

migrations.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.4.21 <= 0.7.0;

contract Migrations {
  address public owner;
  uint public last_completed_migration;

  modifier restricted() {
    if (msg.sender == owner) _;
  }

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

  function setCompleted(uint completed) public restricted {
    last_completed_migration = completed;
  }
}

mycontract.sol

pragma solidity ^0.5.15;

contract MyContract {
    string public myString = "Hello World";
    uint public myUint = 10;
    
    function setString(string memory _mystring) public {
        myString = _mystring;
    }
    
    function setUint(uint _myuint) public {
        myUint = _myuint;
    }
}

MyToken.sol

pragma solidity ^0.5.0;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.3.0/contracts/token/ERC20/ERC20.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.3.0/contracts/token/ERC20/ERC20Detailed.sol";

// This ERC-20 contract mints the specified amount of tokens to the contract creator.
contract MyToken is ERC20, ERC20Detailed {
    constructor(uint256 initialSupply)
        public
        ERC20Detailed("RTOKEN", "RTOK", 18)
    {
        _mint(msg.sender, initialSupply);
    }
}

owned.sol

pragma solidity > 0.5.13;

contract Owned {
    address public owner;
    
    constructor() public {
        owner = msg.sender;
    }
    
    modifier onlyOwner() {
        require(owner == msg.sender, "You are not allowed");
        _;
    }
}

paytoplay.sol

pragma solidity ^0.5.0;

contract PayToPlay {
    event messageWrite(string _text);
    string message;
    
    function write(string memory _message) public payable {
        require(msg.value == 10000000000000000, "Error Require 0.01 BNB to write message");
        message = _message;
        emit messageWrite(message);
    }
    
    function read() public view returns(string memory) {
        return(message);
    }
}

SendMoneyExample.sol

pragma solidity >= 0.5.13;

contract SendMoneyExample {
    
    uint public balanceReceived;
    
    function receiveMoney() public payable {
        balanceReceived += msg.value;
    }
    
    function getBalance() public view returns (uint) {
        return address(this).balance;
    }
    
    function withdrawMoney() public {
        address payable to = msg.sender;
        
        to.transfer(this.getBalance());
        balanceReceived = 0;
        
    }
    
    function withdrawMoneyTo(address payable _sendAddress) public {
        _sendAddress.transfer(this.getBalance());
        balanceReceived = 0;
    }
}

SharedWallet.sol

pragma solidity ^0.6.0;

import "./Allowance.sol";

contract SharedWallet is Allowance {
    event moneyReceived(address indexed _from, uint _amount);
    event moneySend(address indexed _beneficiary, uint _amount);

    
    function getBalance() public view returns (uint) {
        return address(this).balance;
    }
    
    
    function withdraw(address payable _to, uint _amount) public payable OwnerorUser(_to) {
        require(address(this).balance >= _amount, "Not enough funds available for this transaction");
        require(allowance[_to] >= _amount, "requested amount exceeds the allowance");
        reduceAllowance(_to,_amount);
        emit moneySend(_to,_amount);
        _to.transfer(_amount);
    }
    
    function renounceOwnership() public override onlyOwner {
        revert("Can't renounce ownership");
    }
    
    receive() external payable {
        emit moneyReceived(msg.sender,msg.value);
    }
}

simplewallet.sol

pragma solidity ^0.6.0;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol";

contract SimpleWallet is Ownable {
    
    mapping(address => uint) public allowance;
    
    function isOwner() internal view returns(bool) {
         return owner() == msg.sender;
    }
    
    
    modifier OwnerorUser(address _to) {
        require(isOwner() || msg.sender == _to, "You are not allowed");
        _;
    }

    
    function getBalance() public view returns (uint) {
        return address(this).balance;
    }
    
    function reduceAllowance(address _who, uint _amount) internal OwnerorUser(_who) {
        allowance[_who] -= _amount;
    }
    
    function withdraw(address payable _to, uint _amount) public payable OwnerorUser(_to) {
        require(address(this).balance >= _amount, "Not enough funds available for this transaction");
        require(allowance[_to] >= _amount, "requested amount exceeds the allowance");
        reduceAllowance(_to,_amount);
        _to.transfer(_amount);
    }
    
    
    function setAllowance(address _who, uint _amount) public onlyOwner {
        allowance[_who] = _amount;
    }
    
    receive() external payable {
        
    }
}

StartStopUpdateExample.sol

pragma solidity > 0.5.13;

contract StartStopUpdateExample {
    address owner;
    bool public paused;
    
    constructor() public {
        owner = msg.sender;
    }
    
    function sendMoney() public payable {
        
    }
    
    function withdrawAllMoney(address payable _to) public {
        require(msg.sender == owner, "You are not the owner");
        require(paused == false,"The Contract is Paused");
        _to.transfer(address(this).balance);
    }
    
    function setPaused(bool _paused) public {
        require(msg.sender == owner, "You are not the owner");
        paused = _paused;
    }
    
    function destroySmartContract(address payable _to) public {
        require(msg.sender == owner,"You are not the owner");
        selfdestruct(_to);
    }
}

variables.sol

pragma solidity > 0.5.10;

contract WorkingWithVariables {
    uint256 public myVar;
    
    function setMyVar(uint256 _myVar) public {
        myVar = _myVar;
    }
    
    bool public myBool;
    
    function setMyBool(bool _myBool) public {
        myBool = _myBool;
    }
    
    uint8 public myUint8;
    
    function incrementuint8() public {
        myUint8++;
    }
    
    function decrementuint8() public {
        myUint8--;
    }
    
    address public myAddress;
    
    function setAddress(address _address) public {
        myAddress = _address;
    }
    
    function getBalance() public view returns (uint) {
        return myAddress.balance;
    }
    
    string public myString = "hello World";
    
    function setString(string memory _myString) public {
        myString = _myString;
    }
}