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ballot.sol

pragma solidity ^0.4.0;
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.
    function Ballot(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 constant 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

pragma solidity ^0.4.7;
import "remix_tests.sol"; // this import is automatically injected by Remix.
import "./ballot.sol";

contract test3 {
   
    Ballot ballotToTest;
    function beforeAll () {
       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 constant returns (bool) {
        return ballotToTest.winningProposal() == 1;
    }
}

Bank.sol

pragma solidity ^0.4.0;

/**
 * The BankContract contract stores money
 * and returns the balance
 */
contract BankContract {

	uint balance;

	// Since it's payable, no need to pass a value as parameter
	function depositValue () payable {
		balance += msg.value;
	}

	function getBalance() view returns(uint){
		return balance;
	}
	
}

first.sol

pragma solidity ^0.4.0;

contract Dog{
    
    string greeting = "I am a dog! ";
    
    function bark() view returns (string){
        return greeting;
    }
    
    function setGreeting(string _greet){
        greeting = _greet; 
    }
}

homeWork1.sol

pragma solidity ^0.4.0;

contract Person{
    
    string name = "";
    uint age = 0;
    
    function getName() view returns (string){
        return name;
    }
    
    function setName(string _name){
        name = _name; 
    }
    
    function getAge() view returns (uint){
        return age;
    }
    
    function setAge(uint _age){
        age = _age; 
    }
    
    
}

homeWork2.sol

pragma solidity ^0.4.0;

contract PersonsContract{
    
    struct Person{
        string name;
        uint age;
    }
    
    Person[] persons;
    
    function addPerson(string _name,uint _age){
        persons.push(Person(_name,_age));
    }
    
    function getAvgAge() view returns (uint){
        uint acc = 0;
        for(uint i = 0 ; i<persons.length; i++){
            acc = acc + persons[i].age;
        }
        return acc/persons.length;
    }
    
}

Kennel.sol

pragma solidity ^0.4.0;

import './second.sol';

/**
 * The IBankContract interface for bankContract
 */
contract IBankContract {
    function depositValue () payable;
    function getBalance() view returns(uint);
}

contract KennelContract is DogContract{
    
    modifier costs(uint _value) { 
        require (msg.value >= _value); 
        _; 
    }
    
    // Instance of the interface 
    IBankContract BankContract;
    
    function initBank(address _bankAddress) onlyOwner {
        BankContract = IBankContract(_bankAddress);
    }
    
    function transferDog(address _newOwner) payable costs(500){
        // address of the owner of the dog
        address currentOwner = msg.sender;
        // soft error handling
        require(currentOwner != _newOwner);
        // hold the id of the dog while the exchange happens
        uint dogId = ownerToDog[currentOwner];
        // deletes the record of the current Owner from the mapping
        delete(ownerToDog[currentOwner]);
        // create a record with the new owner from the mapping
        ownerToDog[_newOwner] = dogId;
        // strict error handling: this should never happen
        // after assigning a new owner the old owner should be 0 
        // (the default value of a mapping key)
        assert(ownerToDog[currentOwner] == 0);
        
        // sending money to the bank
        BankContract.depositValue.value(msg.value)();
    } 
    
    function getBankBalance() view returns(uint){
        return BankContract.getBalance();
    }
    
    function addDogToKennel(string _name, uint _age){
        addDog(_name, _age);
    }
}

OverUnderFlow.sol

pragma solidity ^0.4.20;

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;
  }
}


contract C {
    using SafeMath for uint256;

    // (2**256 - 1) + 1 = 0
    function overflow() constant returns (uint256 _overflow) {
        uint256 max = 2**256 -1;
        return max.add(1);
    }

    // 0 - 1 = 2**256 - 1
    function underflow() constant returns (uint256 _underflow) {
        uint256 min = 0;
        return min.sub(1);
    }
}

Ownable.sol

pragma solidity ^0.4.24;


/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
  address public owner;


  event OwnershipRenounced(address indexed previousOwner);
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to relinquish control of the contract.
   * @notice Renouncing to ownership will leave the contract without an owner.
   * It will not be possible to call the functions with the `onlyOwner`
   * modifier anymore.
   */
  function renounceOwnership() public onlyOwner {
    emit OwnershipRenounced(owner);
    owner = address(0);
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function transferOwnership(address _newOwner) public onlyOwner {
    _transferOwnership(_newOwner);
  }

  /**
   * @dev Transfers control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function _transferOwnership(address _newOwner) internal {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }
}

second.sol

pragma solidity ^0.4.0;

import './Ownable.sol';

contract DogContract is Ownable{

    // The Dog object
    struct Dog{
        string name;
        uint age;
    }
    
    // Events
    // Events are declared using the event keyword
    // * the arguments are what will be passed to the
    //   interface.

    event dogAdded(address owner, string name, uint id);
    
    // Associate a Dog to an owner represented by an ethereum address
    mapping(address => uint) ownerToDog;

    // Array of objects type Dog
    Dog[] dogs;
    // Array of possible dog names
    string[] dogNames = ["Pako", "Dyna"];
    
    // visibility: in this case out of the possible 4
    // (public, internal, external, private)
    // we choose internal as any contract inheriting from it 
    // should be able to access it only.
    function addDog(string _name, uint _age) internal{
        address owner = msg.sender;
        Dog memory newDog = Dog(_name,_age);
        uint idDog = dogs.push(newDog);
        ownerToDog[owner] = idDog;
        dogAdded(owner, _name, idDog);
    }
    
    function getMyDogName() returns (string) {
        address owner = msg.sender;
        uint dogsId = ownerToDog[owner];
        // dogsId is not normalized
        return dogs[dogsId-1].name;
    }
    
    function getDogName(uint _id) returns (string){
        return dogs[_id].name;
    }
    
    function getDogAge(uint _id) returns (uint){
        return dogs[_id].age;
    }
    
    function addDogName(string _name){
        dogNames.push(_name);
    }
    
    function getDogNameById(uint _id) returns (string){
        return dogNames[_id];
    }
}