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ballot.sol

pragma solidity >=0.4.22 <0.6.0;
contract Ballot {

    struct Voter {
        uint weight;
        bool voted;
        uint8 vote;
        address delegate;
    }
    struct Proposal {
        uint voteCount;
    }

    address chairperson;
    mapping(address => Voter) voters;
    Proposal[] proposals;

    /// Create a new ballot with $(_numProposals) different proposals.
    constructor(uint8 _numProposals) public {
        chairperson = msg.sender;
        voters[chairperson].weight = 1;
        proposals.length = _numProposals;
    }

    /// Give $(toVoter) the right to vote on this ballot.
    /// May only be called by $(chairperson).
    function giveRightToVote(address toVoter) public {
        if (msg.sender != chairperson || voters[toVoter].voted) return;
        voters[toVoter].weight = 1;
    }

    /// Delegate your vote to the voter $(to).
    function delegate(address to) public {
        Voter storage sender = voters[msg.sender]; // assigns reference
        if (sender.voted) return;
        while (voters[to].delegate != address(0) && voters[to].delegate != msg.sender)
            to = voters[to].delegate;
        if (to == msg.sender) return;
        sender.voted = true;
        sender.delegate = to;
        Voter storage delegateTo = voters[to];
        if (delegateTo.voted)
            proposals[delegateTo.vote].voteCount += sender.weight;
        else
            delegateTo.weight += sender.weight;
    }

    /// Give a single vote to proposal $(toProposal).
    function vote(uint8 toProposal) public {
        Voter storage sender = voters[msg.sender];
        if (sender.voted || toProposal >= proposals.length) return;
        sender.voted = true;
        sender.vote = toProposal;
        proposals[toProposal].voteCount += sender.weight;
    }

    function winningProposal() public view returns (uint8 _winningProposal) {
        uint256 winningVoteCount = 0;
        for (uint8 prop = 0; prop < proposals.length; prop++)
            if (proposals[prop].voteCount > winningVoteCount) {
                winningVoteCount = proposals[prop].voteCount;
                _winningProposal = prop;
            }
    }
}

ballot_test.sol

import "remix_tests.sol"; // this import is automatically injected by Remix.
import "./ballot.sol";

contract test3 {
   
    Ballot ballotToTest;
    function beforeAll () public {
       ballotToTest = new Ballot(2);
    }
    
    function checkWinningProposal () public {
        ballotToTest.vote(1);
        Assert.equal(ballotToTest.winningProposal(), uint(1), "1 should be the winning proposal");
    }
    
    function checkWinninProposalWithReturnValue () public view returns (bool) {
        return ballotToTest.winningProposal() == 1;
    }
}

coin.sol

pragma solidity ^0.4.0;

contract PhangBucks {
    
    address public creator;
    mapping(address => uint) public balance;
    // key-value pair
    uint constant public PRICE = 5 * (10**18); // 5 ETH;
    
    function PhangBucks(){
        creator = msg.sender;
    }
    // payable keyword: only able to call this funciton by paying some ether/money
    function createCoin() public payable {
        // only the creator of the coin can create coins;
        require(msg.value > 0 && msg.value % 5 == 0);
        balance[msg.sender] += msg.value/PRICE;
    }
    
    function transfer(address receiver, uint amount) public {
        if (balance[msg.sender] >= amount && amount > 0){
            balance[msg.sender] -= amount;
            balance[receiver] += amount;
        }
        
    }
}

first.sol

pragma solidity ^0.4.0; // compatible from version 0.4.0 till 0.4.x 



// store a number on the ethereum blockchain
contract Store {
    uint x; // unsigned integer
    
    function set(uint i) public {
        x = i;
    }
    
    function get() public view returns(uint) {
        return x;
    }
}

instructor.sol

pragma solidity ^0.4.0;

contract Instructor{
    address creator;
    string name;
    uint age;

    function Instructor(){
        creator = msg.sender;
    }
    
    function setInstructor(string newName, uint newAge) public {
        name = newName;
        age = newAge;
    }
    
    function getInstructor() public view returns (string, uint) {
        return (name, age);
    }
}

moneroScam.sol

pragma solidity ^0.4.0;
import "browser/safeMath.sol";


contract MoneroGoldScam {
    //using SafeMath for uint;
    uint totalSupply;
    
    function set(uint initialVal) public {
        totalSupply = initialVal;
    }
    
    function deduct() public {
        totalSupply = SafeMath.sub(totalSupply,1);
    }
    
    function get() public view returns(uint){
        return totalSupply;
    }
}

safeMath.sol

pragma solidity ^0.4.0;

/**
 * @title SafeMath
 * @dev Unsigned math operations with safety checks that revert on error
 */
library SafeMath {
    /**
     * @dev Multiplies two unsigned integers, reverts on overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring '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;
        }

        uint256 c = a * b;
        require(c / a == b);

        return c;
    }

    /**
     * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Adds two unsigned integers, reverts on overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }

    /**
     * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
     * reverts when dividing by zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }
}

second.sol

pragma solidity ^0.4.0;

contract HelloWorld{
    string greeting;
    address  public creator;
    
    // constructor function, called only once in its lifetime, at the time of deploymnent of the smart contract
    function HelloWorld(string message){
        
        creator = msg.sender;       // whichever address that sent a message to the function, to know who created the smart contract
        greeting = message;
    }
    
    // view keyword tells the blockchain it only reads from it
    function sayHello() public view returns(string){
        return greeting;
    }
}