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1_Storage.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.8.0;

/**
 * @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

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.8.0;

/**
 * @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() {
        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

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.8.0;

/** 
 * @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) {
        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;
    }
}

Libraries.sol

pragma solidity ^0.7.4;


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

library HelperFunctions{
    using SafeMath for uint;
    function SumArray(uint[] memory _array ) 
    public 
    returns(uint)
    {
            uint ArraySum;
        for(uint i=0; i<_array.length; i++){
            ArraySum.add(_array[i]);
            return(ArraySum);
        } 
    }
}

contract Libraries{
    
    //all SafeMath functions are now USABLE for unsigned integers
    using SafeMath for uint;
    using HelperFunctions for uint[];
    uint[] public data;
    uint public constant tokenRate = 2;
    mapping(address => uint) public tokenBalance;
    constructor() payable {
        tokenBalance[msg.sender] = msg.value.div(tokenRate);
    }
    
    function totalBalance(uint[] memory _balances) public  returns(uint){
        return(_balances.SumArray());
    }
    
    
}

mapping.sol

pragma solidity ^0.5.13;

contract Mapping{
    
    struct Profile{
        string name;
        uint timestamps;
        //assume a profile has multiple wallets
        mapping(uint => address) myWallets;
    }
    
    
    mapping(address => bool) public AddressToBool;
    mapping(address => uint) public BalanceReceived;
    
    function allowAddress(address _allowed) public{
        AddressToBool[_allowed]= true;
    }
    
    function setMyAddress() public{
        AddressToBool[msg.sender] = true;
    }
}

MoneyContract.sol

pragma solidity ^0.5.12;


contract SendMoney{
    
    uint256 public Balance ;
    function receiveMoney() public payable{
        Balance = address(this).balance;
    }
    
    function getBalance() public view returns(uint){
        
        return address(this).balance;
    }
    
    function withdraw(uint _myWithdrawal) public{
        // use payable to make an address payable....
        address payable sender = msg.sender;
        sender.transfer(_myWithdrawal);
    }
    
    function withdrawMoneyTo(address payable _myAddress) public{
        _myAddress.transfer(this.getBalance());
    }
    
    //attempt at exchanging 
    function exchangeMoney(address payable _myCounterparty,uint amountSent, uint amountReceived) public{
        address payable _myAddress =  msg.sender;
        // smart contract needs to receive both amounts.....
        _myCounterparty.transfer(amountSent);
        _myAddress.transfer(amountReceived);
    }
    

}

sandbox1.sol

pragma solidity ^0.7.4;

import './2_Owner.sol';

contract Treasury is Owner{
    
    address private _owner;
    uint private conversionRate;
    uint public TotalAmount;
    
    constructor(){
        _owner = msg.sender;
        conversionRate = 2;
    }
    
    
    struct Payment{
        uint timestamp;
        uint amount;
    }
    struct Profile{
        uint id ;
        string name;
        uint profileValue;
        mapping(uint => Payment) myPayments;
    }
    
    mapping(address => Profile) public myProfile;
    
    event Wallet(uint indexed id, address _owner, uint totalAmount);
    event UpdateMessage(uint indexed id, string message, uint value);
    
    
    modifier logger(){
        Update
        
    }
    
    function deposit() payable public{
        require(_owner == msg.sender, "Only those who deployed have access.");
        assert(msg.value + TotalAmount > TotalAmount);
        TotalAmount += msg.value;
        
    }
    
    //not sure what indexed does
    
    fallback() external{
        wow = data;
        emit UpdateMessage(1, myProfile[msg.sender].name, 0);
        
    }
    
    
    
}

SharedWallet.sol

pragma solidity ^0.6.0;
/* Wallet where a central party can:
Deposit Money (Any Amount)
Approve request to withdraw


Users can only:
Request to withdraw money (any amount)

*/

//This is bad practice. 
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol";

contract Permissions{
    address private sysAdmin;
    address[] public memberList;
    struct addressStruct{
        bool isMember;
        string name;
        uint numWithdraws;
        uint amount;
    }
    
    mapping(address => addressStruct) public addressDetails;
    
    
    constructor() public{
        sysAdmin = msg.sender;
    }
    
    modifier AdminOnly{
        require(msg.sender == sysAdmin, "You do not have rights to this function");
        _;
    }
    
    modifier MemberOnly{
        require(addressDetails[msg.sender].isMember == true, "You're not yet a member");
        _;
    }
    
    function AddMember(address _member) AdminOnly public{
        addressDetails[_member].isMember = true;
    }
    
}


contract WalletInteractions is Permissions{
    using SafeMath for uint;
    uint public totalWalletBalance;
    struct withdrawalRequest{
        address withdrawerAddress;
        uint amount;
        bool isFulfilled;
    }
    
    withdrawalRequest[] public withdrawalList;
    
    event BalanceUpdate(string action, address indexed actionAddress, uint amount, uint balanceLeft);
    
    function deposit() payable external AdminOnly{
        totalWalletBalance.add(msg.value);
        emit BalanceUpdate("Deposit", msg.sender, msg.value, totalWalletBalance);
    }
    
    function requestWithdraw(uint _amount) external MemberOnly returns (uint rowNumber)  {
        require(_amount >0 , "Please input a positive value");
        withdrawalRequest memory newRequest;
        newRequest = withdrawalRequest(msg.sender, _amount, false);
        
        //push doesn't work here. no idea why
        withdrawalList.push(newRequest);
        return withdrawalList.length -1;
        
    }
    
    function approveWithdraw(uint _index) external AdminOnly{
        uint requestAmount = withdrawalList[_index].amount;
        address payable requestAddress = payable(withdrawalList[_index].withdrawerAddress);
        assert(addressDetails[requestAddress].isMember == true);
        assert(totalWalletBalance - requestAmount <= totalWalletBalance);
        
        totalWalletBalance.sub(requestAmount);
        
        // I suppose pop is a vulnerability. So instead of deleting from your array list, you'd rather change boolean of whether the withdrawal is fulfilled
        withdrawalList[_index].isFulfilled = true;
        requestAddress.transfer(requestAmount);
        emit BalanceUpdate("Withdraw", requestAddress, requestAmount, totalWalletBalance);
    }
    
}

StartStopUpdate.sol

pragma solidity ^0.5.13;

//This is about authority control 
//Save owner of address during deployment

contract StartStopUpdate{
    
    //notice how they are not public
    address owner;
    bool paused;
    //Constructors are called ONLY ONCE
    constructor() public{
        owner = msg.sender;
    }
    
    function togglePause() public{
        require(owner == msg.sender,"You are not an owner");
        paused = !paused;
    }
    
    function withdrawAllMoney(address payable _to) public{
        require(owner == msg.sender,"You are not an owner");
        require(!paused, "Contract is not functioning");
        _to.transfer(address(this).balance);
    }
    
    //destroy smart Contract
    function destroySmartContract(address payable _to) public{
        require(owner == msg.sender, "Only owner can destroy");
        //selfdestruct takes a address to send a fund to
        selfdestruct(_to);
    }
}

StructPractice.sol

pragma solidity ^0.5.13;


contract StructPractice{
    struct Payment{
        uint amount;
        uint timestamp;
    }
    
    struct Balance{
        uint amount;
        uint numPayments;
        mapping(uint => Payment) payments;
    }
    mapping(address => Balance) public AddressBalance;
    address public Owner;

    constructor() public{
        Owner = msg.sender;
        
    }
    
    function sendMoney() payable public{
        //make sure balance variable cannot be 
        AddressBalance[msg.sender].amount += msg.value;
        AddressBalance[msg.sender].payments[AddressBalance[msg.sender].numPayments] = Payment(msg.value, now);
        AddressBalance[msg.sender].numPayments++;
    }
    
    function withdrawMoney(address payable _to, uint amount) public{
        require(AddressBalance[msg.sender].amount >= amount, "Not enough funds");
        //notice the difference, even though they appear like similar logic
        assert(AddressBalance[msg.sender].amount > AddressBalance[msg.sender].amount -amount);
        AddressBalance[msg.sender].amount -= amount;
        AddressBalance[msg.sender].payments[AddressBalance[msg.sender].numPayments] = Payment(amount, now);
        AddressBalance[msg.sender].numPayments++;
        _to.transfer(amount);
    }
    
    function fallback() payable external returns(string){
        // Handle contract execution
        require(msg.data.length == 0);
        // So that only money is sent, no malicious data
        string memory data = msg.data;
        return data;
    }
    
    //receive transaction without calling function... deprecated?
    
    receive () external payable{
        
    }
    
    //assuming you only want to call this internally, within this smart contract
    function sum(int _amount1, int _amount2) internal pure returns(int){
        return amount1+amount2;
    }
}

StructTest.sol

pragma solidity ^0.5.13;

contract StructTest{
    struct Balance{
        uint value;
        mapping(uint => Payment) Payments;
    }
    
    
    struct Payment{
        uint value;
        uint time;
        mapping(uint => address) paidTo;
    }
    
    mapping(address => Balance) public addressWallets;
    
    address public owner;
    //set initial wallet owner
    
    //Use constructor
    
    constructor() public{
        owner = msg.sender;
    }
    
    
    function viewWallets() public view returns (uint){
        require(owner == msg.sender, "You must be the owner of this contract to view your wallet");
        return(addressWallets[msg.sender].value);
    }
    
    function sendMoney(uint amount, address payable _to) public {
        require(owner == msg.sender, "You must be the owner of this contract to view your wallet");
        Payment memory payment = Payment(amount, now);
        payment.paidTo[0] = _to;
    }
}

Token.sol

pragma solidity >=0.7.0;

import "./2_Owner.sol";

contract TokenContract is Owner{
    uint public Circulation ;
    address public Contractor ;
    uint public EthTokenRate;
    uint public ReserveBalance;
    constructor() {
        Contractor = msg.sender;
        Circulation = 1000000000000000;
        EthTokenRate = 2;
    }
    
    event TokenExchanged(address _from, uint amount, uint indexed _id);
    
    
    modifier onlyHighValue(){
        require(msg.value >= 10000, "value too low!");
        _;
    }
    
    function ethToToken(uint eth) public view returns(uint){
        return eth/EthTokenRate;
    }
    function exchange() payable external onlyHighValue isOwner{
        uint mintAmount;
        mintAmount = ethToToken(msg.value);
        ReserveBalance -= mintAmount;
        emit TokenExchanged(msg.sender, mintAmount, 1);
    }
    
    fallback() payable external{
        require(msg.data.length == 0, "only value allowed");
    }
    
    
    
    
    
}

UdemyContract.sol

pragma solidity ^0.5.11;

// State change only happens with transaction + mining


contract WorkingWithVariables{
    uint256 public myUint;
    bool public myBool;
    uint8 public myUint8;
    string public myString;
    address public myAddress;
    
    //Setter function
    function setmyUint(uint _myUint) public{
        myUint = _myUint;
    }
    function setmyBool(bool _myBool) public{
        myBool = _myBool;
    }
    
    function increment() public{
        myUint8++;
    }
    
    function setmyString(string memory _myString) public{
        myString = _myString;
    }
    

    
    function setAddress(address _myAddress) public{
        myAddress = _myAddress;
    }
    
    function getAddressBalance() public view returns(uint){
        return myAddress.balance;
    }

}