Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime. Load this file by pasting this gists URL or ID at https://remix.ethereum.org/#version=soljson-v0.6.6+commit.6c089d02.js&optimize=false&gist=

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;
    }
}

Counter.sol

pragma solidity ^0.6.0; 

contract Counter {
    uint public count = 0;
    
    function incrementCount() public {
        count++;        
    }
    
    
}

HotelRoom.sol

pragma solidity ^0.6.0;

contract HotelRoom {

// Ether - pay smart contracts
// Modifiers
// Visibility
// Events
// Enums

    enum Statuses { Vacant, Occupied }
    Statuses currentStatus;
    
    event Occupy(address _occupant, uint _value);
    
    address payable public owner;
    
    constructor() public  {
        owner = msg.sender;
        currentStatus = Statuses.Vacant;
    }

    modifier onlyWhileVacant {
        require(currentStatus == Statuses.Vacant, "Currently Occupied.");
        _;
    }
    
    modifier costs(uint _amount) {
        require(msg.value >= _amount, "Not enough Ether provided.");
        _;
    }
    
    
    receive() external payable onlyWhileVacant costs(2 ether) {
        currentStatus = Statuses.Occupied;
        owner.transfer(msg.value);
        emit Occupy(msg.sender, msg.value);
    }

    
}

MyContract.sol

pragma solidity ^0.6.0;

// Variables
// State Varialbes and Local Varialbes
// State Variables are stored on the Blockchain
// Data Types
// Custom Data Structures


contract MyContract {
    // State Variable
    int public myInt = -1;
    uint256 public myUint = 1;
    
    string public myString = "Greetings, Galaxy!";
    bytes32 public myByte32 = "Greetings, Galaxy!";
    
    address public myAddress = 0x5a0Fcb45d2Ffa6C2e9ec1aC3289D56537792F956;
    
    struct Person {
        uint ID;
        string ballot;
    }
    
    Person public aPerson = Person(1,"Greetings, Galaxy!");
    
    
    function getValue() public pure returns(uint) {
        uint value = 1;
        return value;
    }
    
    
    
    
}

MyContract2.sol

pragma solidity ^0.6.0;

contract MyContract2 {
    // Arrays
    // Mapping
    
    uint[] public uintArray = [1,2,3];
    string[] public stringArray = ["apple", "banana", "carrot"];
    string[] public values;
    uint[][] public array2D = [ [1,2,3], [4,5,6] ];
    
    
    function addValue(string memory _value) public {
        values.push(_value);
    }
    
    function valueCount() public view returns(uint) {
        return values.length;
    }
    
    
    
}

MyContract3.sol

pragma solidity ^0.6.0;

contract MyContract3 {
    // Mappings
    mapping(uint => string) public names;
    mapping(uint => Book ) public books;
    mapping(address => mapping(uint => Book )) public ownedBooks;
    
    
    struct Book {
        string title;
        string author;
    }
    
    constructor() public {
        names[1] = "Adam";
        names[2] = "Bruce";
        names[3] = "Carl";
    }
    
    function addBook(uint _id, string memory _title, string memory _author) public {
        books[_id] = Book(_title, _author);
        
    }
    
    function addOwnedBook(uint _id, string memory _title, string memory _author) public {
        ownedBooks[msg.sender][_id] = Book(_title, _author);
    }
    

    
}

MyContracts4.sol

pragma solidity ^0.6.0;

contract MyContract4 {
    // Conditionals
    
    uint[] public numbers =[1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
    
    
    address public owner;
    
    constructor() public {
        owner = msg.sender;
        
    }
    
    function isOwner() public view returns(bool) {
        return (msg.sender == owner);
    }
    
    function countEvenNumbers() public view returns(uint) {
        
        uint count = 0;
        
        for (uint i = 0; i < numbers.length; i++) {
            if (isEvenNumber(numbers[i])) {
                count++;
            }
        }
        
        return count;
    }
    
    
    function isEvenNumber(uint _number) public view returns(bool) {
        if (_number % 2 == 0) {
            return true;
        } else {
            return false;
        }
    }
    
    // Loops
    
    

    
}

MyContracts5.sol

// this line is added to create a gist. Empty file is not allowed.