pragma solidity ^ 0.4.17; library SafeMath { function mul(uint a, uint b) internal pure returns(uint) { uint c = a * b; assert(a == 0 || c / a == b); return c; } function sub(uint a, uint b) internal pure returns(uint) { assert(b <= a); return a - b; } function add(uint a, uint b) internal pure returns(uint) { uint c = a + b; assert(c >= a && c >= b); return c; } } contract ERC20 { uint public totalSupply; function balanceOf(address who) public view returns(uint); function allowance(address owner, address spender) public view returns(uint); function transfer(address to, uint value) public returns(bool ok); function transferFrom(address from, address to, uint value) public returns(bool ok); function approve(address spender, uint value) public returns(bool ok); event Transfer(address indexed from, address indexed to, uint value); event Approval(address indexed owner, address indexed spender, uint value); } /** * @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 OwnershipTransferred(address indexed previousOwner, address indexed newOwner); /** * @dev The Ownable constructor sets the original `owner` of the contract to the sender * account. */ function Ownable() 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 transfer control of the contract to a newOwner. * @param newOwner The address to transfer ownership to. */ function transferOwnership(address newOwner) onlyOwner public { require(newOwner != address(0)); OwnershipTransferred(owner, newOwner); owner = newOwner; } } /** * @title Pausable * @dev Base contract which allows children to implement an emergency stop mechanism. */ contract Pausable is Ownable { event Pause(); event Unpause(); bool public paused = false; /** * @dev Modifier to make a function callable only when the contract is not paused. */ modifier whenNotPaused() { require(!paused); _; } /** * @dev Modifier to make a function callable only when the contract is paused. */ modifier whenPaused() { require(paused); _; } /** * @dev called by the owner to pause, triggers stopped state */ function pause() public onlyOwner whenNotPaused { paused = true; Pause(); } /** * @dev called by the owner to unpause, returns to normal state */ function unpause() public onlyOwner whenPaused { paused = false; Unpause(); } } // Whitelist smart contract // This smart contract keeps list of addresses to whitelist contract WhiteList is Ownable { mapping(address => bool) public whiteList; uint public totalWhiteListed; //white listed users number event LogWhiteListed(address indexed user, uint whiteListedNum); event LogWhiteListedMultiple(uint whiteListedNum); event LogRemoveWhiteListed(address indexed user); // @notice it will return status of white listing // @return true if user is white listed and false if is not function isWhiteListed(address _user) external view returns (bool) { return whiteList[_user]; } // @notice it will remove whitelisted user // @param _contributor {address} of user to unwhitelist function removeFromWhiteList(address _user) external onlyOwner() returns (bool) { require(whiteList[_user] == true); whiteList[_user] = false; totalWhiteListed--; LogRemoveWhiteListed(_user); return true; } // @notice it will white list one member // @param _user {address} of user to whitelist // @return true if successful function addToWhiteList(address _user) external onlyOwner() returns (bool) { if (whiteList[_user] != true) { whiteList[_user] = true; totalWhiteListed++; LogWhiteListed(_user, totalWhiteListed); } return true; } // @notice it will white list multiple members // @param _user {address[]} of users to whitelist // @return true if successful function addToWhiteListMultiple(address[] _users) external onlyOwner() returns (bool) { for (uint i = 0; i < _users.length; ++i) { if (whiteList[_users[i]] != true) { whiteList[_users[i]] = true; totalWhiteListed++; } } LogWhiteListedMultiple(totalWhiteListed); return true; } } // @note this contract can be inherited by Crowdsale and TeamAllocation contracts and // control release of tokens through even time release based on the inputted duration time interval contract TokenVesting is Ownable { using SafeMath for uint; struct TokenHolder { uint weiReceived; // amount of ETH contributed uint tokensToSend; // amount of tokens sent bool refunded; // true if user has been refunded uint releasedAmount; // amount released through vesting schedule bool revoked; // true if right to continue vesting is revoked } event Released(uint256 amount, uint256 tokenDecimals); event ContractUpdated(bool done); uint256 public cliff; // time in when vesting should begin uint256 public startCountDown; // time when countdown starts uint256 public duration; // duration of period in which vesting takes place Token public token; // token contract containing tokens mapping(address => TokenHolder) public tokenHolders; //tokenHolder list WhiteList public whiteList; // whitelist contract uint256 public presaleBonus; // @note constructor /** function TokenVesting(uint256 _start, uint256 _cliff, uint256 _duration) public { require(_cliff <= _duration); duration = _duration; cliff = _start.add(_cliff); startCountDown = _start; ContractUpdated(true); } */ // @notice Specify address of token contract // @param _tokenAddress {address} address of token contract // @return res {bool} function initilizeVestingAndTokenAndWhiteList(Token _tokenAddress, uint256 _start, uint256 _cliff, uint256 _duration, uint256 _presaleBonus, WhiteList _whiteList) external onlyOwner() returns(bool res) { require(_cliff <= _duration); require(_tokenAddress != address(0)); duration = _duration; cliff = _start.add(_cliff); startCountDown = _start; token = _tokenAddress; whiteList = _whiteList; presaleBonus = _presaleBonus; ContractUpdated(true); return true; } // @notice Specify address of token contract // @param _tokenAddress {address} address of token contract // @return res {bool} function initilizeVestingAndToken(Token _tokenAddress, uint256 _start, uint256 _cliff, uint256 _duration, uint256 _presaleBonus ) external onlyOwner() returns(bool res) { require(_cliff <= _duration); require(_tokenAddress != address(0)); duration = _duration; cliff = _start.add(_cliff); startCountDown = _start; token = _tokenAddress; presaleBonus = _presaleBonus; ContractUpdated(true); return true; } function returnVestingSchedule() external view returns (uint, uint, uint) { return (duration, cliff, startCountDown); } // @note owner can revoke access to continue vesting of tokens // @param _user {address} of user to revoke their right to vesting function revoke(address _user) public onlyOwner() { TokenHolder storage tokenHolder = tokenHolders[_user]; tokenHolder.revoked = true; } function vestedAmountAvailable() public view returns (uint amount, uint decimals) { TokenHolder storage tokenHolder = tokenHolders[msg.sender]; uint tokensToRelease = vestedAmount(tokenHolder.tokensToSend); // if (tokenHolder.releasedAmount + tokensToRelease > tokenHolder.tokensToSend) // return (tokenHolder.tokensToSend - tokenHolder.releasedAmount, token.decimals()); // else return (tokensToRelease - tokenHolder.releasedAmount, token.decimals()); } // @notice Transfers vested available tokens to beneficiary function release() public { TokenHolder storage tokenHolder = tokenHolders[msg.sender]; // check if right to vesting is not revoked require(!tokenHolder.revoked); uint tokensToRelease = vestedAmount(tokenHolder.tokensToSend); uint currentTokenToRelease = tokensToRelease - tokenHolder.releasedAmount; tokenHolder.releasedAmount += currentTokenToRelease; token.transfer(msg.sender, currentTokenToRelease); Released(currentTokenToRelease, token.decimals()); } // @notice this function will determine vested amount // @param _totalBalance {uint} total balance of tokens assigned to this user // @return {uint} amount of tokens available to transfer function vestedAmount(uint _totalBalance) public view returns (uint) { if (now < cliff) { return 0; } else if (now >= startCountDown.add(duration)) { return _totalBalance; } else { return _totalBalance.mul(now.sub(startCountDown)) / duration; } } } // Crowdsale Smart Contract // This smart contract collects ETH and in return sends tokens to the Backers contract Crowdsale is Pausable, TokenVesting { using SafeMath for uint; address public multisigETH; // Multisig contract that will receive the ETH address public commissionAddress; // address to deposit commissions uint public tokensForTeam; // tokens for the team uint public ethReceivedPresale; // Number of ETH received in presale uint public ethReceivedMain; // Number of ETH received in main sale uint public totalTokensSent; // Number of tokens sent to ETH contributors uint public tokensSentMain; uint public tokensSentPresale; uint public tokensSentDev; uint public startBlock; // Crowdsale start block uint public endBlock; // Crowdsale end block uint public maxCap; // Maximum number of token to sell uint public minCap; // Minimum number of ETH to raise uint public minContributionMainSale; // Minimum amount to contribute in main sale uint public minContributionPresale; // Minimum amount to contribut in presale uint public maxContribution; bool public crowdsaleClosed; // Is crowdsale still on going uint public tokenPriceWei; uint public refundCount; uint public totalRefunded; uint public campaignDurationDays; // campaign duration in days uint public firstPeriod; uint public secondPeriod; uint public thirdPeriod; uint public firstBonus; uint public secondBonus; uint public thirdBonus; uint public multiplier; uint public status; Step public currentStep; // To allow for controlled steps of the campaign // Looping through Backer //mapping(address => Backer) public backers; //backer list address[] public holdersIndex; // to be able to itarate through backers when distributing the tokens address[] public devIndex; // to be able to itarate through backers when distributing the tokens // @notice to set and determine steps of crowdsale enum Step { FundingPreSale, // presale mode FundingMainSale, // public mode Refunding // in case campaign failed during this step contributors will be able to receive refunds } // @notice to verify if action is not performed out of the campaing range modifier respectTimeFrame() { if ((block.number < startBlock) || (block.number > endBlock)) revert(); _; } modifier minCapNotReached() { if (totalTokensSent >= minCap) revert(); _; } // Events event LogReceivedETH(address indexed backer, uint amount, uint tokenAmount); event LogStarted(uint startBlockLog, uint endBlockLog); event LogFinalized(bool success); event LogRefundETH(address indexed backer, uint amount); event LogStepAdvanced(); event LogDevTokensAllocated(address indexed dev, uint amount); event LogNonVestedTokensSent(address indexed user, uint amount); // Crowdsale {constructor} // @notice fired when contract is crated. Initilizes all constnat variables. function Crowdsale(uint _decimalPoints, address _multisigETH, uint _toekensForTeam, uint _minContributionPresale, uint _minContributionMainSale, uint _maxContribution, uint _maxCap, uint _minCap, uint _tokenPriceWei, uint _campaignDurationDays, uint _firstPeriod, uint _secondPeriod, uint _thirdPeriod, uint _firstBonus, uint _secondBonus, uint _thirdBonus) public { multiplier = 10**_decimalPoints; multisigETH = _multisigETH; tokensForTeam = _toekensForTeam * multiplier; minContributionPresale = _minContributionPresale; minContributionMainSale = _minContributionMainSale; maxContribution = _maxContribution; maxCap = _maxCap * multiplier; minCap = _minCap * multiplier; tokenPriceWei = _tokenPriceWei; campaignDurationDays = _campaignDurationDays; firstPeriod = _firstPeriod; secondPeriod = _secondPeriod; thirdPeriod = _thirdPeriod; firstBonus = _firstBonus; secondBonus = _secondBonus; thirdBonus = _thirdBonus; //TODO replace this address below with correct address. commissionAddress = 0x326B5E9b8B2ebf415F9e91b42c7911279d296ea1; //commissionAddress = 0x853A3F142430658A32f75A0dc891b98BF4bDF5c1; currentStep = Step.FundingPreSale; } // @notice to populate website with status of the sale function returnWebsiteData() external view returns(uint, uint, uint, uint, uint, uint, uint, uint, uint, uint, bool, bool, uint, Step) { return (startBlock, endBlock, numberOfBackers(), ethReceivedPresale + ethReceivedMain, maxCap, minCap, totalTokensSent, tokenPriceWei, minContributionPresale, minContributionMainSale, paused, crowdsaleClosed, token.decimals(), currentStep); } // @notice this function will determine status of crowdsale function determineStatus() external view returns (uint) { if (crowdsaleClosed) // ICO finihsed return 1; if (block.number < endBlock && totalTokensSent < maxCap - 100) // ICO in progress return 2; if (totalTokensSent < minCap && block.number > endBlock) // ICO failed return 3; if (endBlock == 0) // ICO hasn't been started yet return 4; return 0; } // {fallback function} // @notice It will call internal function which handels allocation of Ether and calculates tokens. function () public payable { contribute(msg.sender); } // @notice to allow for contribution from interface function contributePublic() external payable { contribute(msg.sender); } // @notice set the step of the campaign from presale to public sale // contract is deployed in presale mode // WARNING: there is no way to go back function advanceStep() external onlyOwner() { currentStep = Step.FundingMainSale; LogStepAdvanced(); } // @notice It will be called by owner to start the sale function start() external onlyOwner() { startBlock = block.number; endBlock = startBlock + (4*60*24*campaignDurationDays); // assumption is that one block takes 15 sec. crowdsaleClosed = false; LogStarted(startBlock, endBlock); } // @notice This function will finalize the sale. // It will only execute if predetermined sale time passed or all tokens are sold. function finalize() external onlyOwner() { require(!crowdsaleClosed); require(block.number >= endBlock || totalTokensSent > maxCap - 1000); // - 1000 is used to allow closing of the campaing when contribution is near // finished as exact amount of maxCap might be not feasible e.g. you can't easily buy few tokens. // when min contribution is 0.1 Eth. require(totalTokensSent >= minCap); crowdsaleClosed = true; // transfer commission portion to the platform commissionAddress.transfer(determineCommissions()); // transfer remaning funds to the campaign wallet multisigETH.transfer(this.balance); /*if (!token.transfer(owner, token.balanceOf(this))) revert(); // transfer tokens to admin account if (!token.burn(this, token.balanceOf(this))) revert(); // burn all the tokens remaining in the contract */ token.unlock(); // release lock from transfering tokens. LogFinalized(true); } // @notice it will allow contributors to get refund in case campaign failed // @return {bool} true if successful function refund() external whenNotPaused returns (bool) { uint totalEtherReceived = ethReceivedPresale + ethReceivedMain; require(totalEtherReceived < minCap); // ensure that campaign failed require(this.balance > 0); // contract will hold 0 ether at the end of campaign. // contract needs to be funded through fundContract() TokenHolder storage backer = tokenHolders[msg.sender]; require(backer.weiReceived > 0); // ensure that user has sent contribution require(!backer.refunded); // ensure that user hasn't been refunded yet backer.refunded = true; // save refund status to true refundCount++; totalRefunded += backer.weiReceived; if (!token.burn(msg.sender, backer.tokensToSend)) // burn tokens revert(); msg.sender.transfer(backer.weiReceived); // send back the contribution LogRefundETH(msg.sender, backer.weiReceived); return true; } // @notice allocate tokens to dev/team/advisors // @param _dev {address} // @param _amount {uint} amount of tokens function devAllocation(address _dev, uint _amount) external onlyOwner() returns (bool) { require(_dev != address(0)); require(crowdsaleClosed); require(totalTokensSent.add(_amount) <= token.totalSupply()); devIndex.push(_dev); TokenHolder storage tokenHolder = tokenHolders[_dev]; tokenHolder.tokensToSend = _amount; tokensSentDev += _amount; totalTokensSent += _amount; LogDevTokensAllocated(_dev, _amount); // Register event return true; } // @notice Failsafe drain function drain(uint _amount) external onlyOwner() { owner.transfer(_amount); } // @notice transfer tokens which are not subject to vesting // @param _recipient {addres} // @param _amont {uint} amount to transfer function transferTokens(address _recipient, uint _amount) external onlyOwner() returns (bool) { require(_recipient != address(0)); if (!token.transfer(_recipient, _amount)) revert(); LogNonVestedTokensSent(_recipient, _amount); } // @notice determine amount of commissions for the platform function determineCommissions() public view returns (uint) { if (this.balance <= 500 ether) { return (this.balance * 10)/100; }else if (this.balance <= 1000 ether) { return (this.balance * 8)/100; }else if (this.balance < 10000 ether) { return (this.balance * 6)/100; }else { return (this.balance * 6)/100; } } // @notice return number of contributors // @return {uint} number of contributors function numberOfBackers() public view returns (uint) { return holdersIndex.length; } // @notice It will be called by fallback function whenever ether is sent to it // @param _backer {address} address of beneficiary // @return res {bool} true if transaction was successful function contribute(address _backer) internal whenNotPaused respectTimeFrame returns(bool res) { //require(msg.value <= maxContribution); if (whiteList != address(0)) // if whitelist initialized verify member whitelist status require(whiteList.isWhiteListed(_backer)); // ensure that user is whitelisted uint tokensToSend = calculateNoOfTokensToSend(); // calculate number of tokens // Ensure that max cap hasn't been reached require(totalTokensSent + tokensToSend <= maxCap); TokenHolder storage backer = tokenHolders[_backer]; if (backer.weiReceived == 0) holdersIndex.push(_backer); if (Step.FundingMainSale == currentStep) { // Update the total Ether received and tokens sent during public sale require(msg.value >= minContributionMainSale); // stop when required minimum is not met ethReceivedMain = ethReceivedMain.add(msg.value); tokensSentMain += tokensToSend; }else { require(msg.value >= minContributionPresale); // stop when required minimum is not met ethReceivedPresale = ethReceivedPresale.add(msg.value); tokensSentPresale += tokensToSend; } backer.tokensToSend += tokensToSend; backer.weiReceived = backer.weiReceived.add(msg.value); totalTokensSent += tokensToSend; // tokens are not transferrd to contributors during this phase // tokens will be transferred based on the vesting schedule, when contributor // calls release() function of this contract LogReceivedETH(_backer, msg.value, tokensToSend); // Register event return true; } // @notice This function will return number of tokens based on time intervals in the campaign function calculateNoOfTokensToSend() internal view returns (uint) { uint tokenAmount = msg.value.mul(multiplier) / tokenPriceWei; if (Step.FundingMainSale == currentStep) { if (block.number <= startBlock + firstPeriod) { return tokenAmount + tokenAmount.mul(firstBonus) / 100; }else if (block.number <= startBlock + secondPeriod) { return tokenAmount + tokenAmount.mul(secondBonus) / 100; }else if (block.number <= startBlock + thirdPeriod) { return tokenAmount + tokenAmount.mul(thirdBonus) / 100; }else { return tokenAmount; } }else return tokenAmount + tokenAmount.mul(presaleBonus) / 100; } } // The token contract Token is ERC20, Ownable { using SafeMath for uint; // Public variables of the token string public name; string public symbol; uint public decimals; // How many decimals to show. string public version = "v0.1"; uint public totalSupply; bool public locked; address public crowdSaleAddress; mapping(address => uint) public balances; mapping(address => mapping(address => uint)) public allowed; // Lock transfer during the ICO modifier onlyUnlocked() { if (msg.sender != crowdSaleAddress && locked && msg.sender != owner) revert(); _; } modifier onlyAuthorized() { if (msg.sender != crowdSaleAddress && msg.sender != owner) revert(); _; } // The Token constructor function Token(uint _initialSupply, string _tokenName, uint _decimalUnits, string _tokenSymbol, string _version, address _crowdSaleAddress) public { locked = true; // Lock the transfer of tokens during the crowdsale totalSupply = _initialSupply * (10**_decimalUnits); name = _tokenName; // Set the name for display purposes symbol = _tokenSymbol; // Set the symbol for display purposes decimals = _decimalUnits; // Amount of decimals for display purposes version = _version; crowdSaleAddress = _crowdSaleAddress; balances[crowdSaleAddress] = totalSupply; } function unlock() public onlyAuthorized { locked = false; } function lock() public onlyAuthorized { locked = true; } function burn(address _member, uint256 _value) public onlyAuthorized returns(bool) { require(balances[_member] >= _value); balances[_member] -= _value; totalSupply -= _value; Transfer(_member, 0x0, _value); return true; } // @notice transfer tokens to given address // @param _to {address} address or recipient // @param _value {uint} amount to transfer // @return {bool} true if successful function transfer(address _to, uint _value) public onlyUnlocked returns(bool) { require(_to != address(0)); require(balances[msg.sender] >= _value); balances[msg.sender] -= _value; balances[_to] += _value; Transfer(msg.sender, _to, _value); return true; } // @notice transfer tokens from given address to another address // @param _from {address} from whom tokens are transferred // @param _to {address} to whom tokens are transferred // @param _value {uint} amount of tokens to transfer // @return {bool} true if successful function transferFrom(address _from, address _to, uint256 _value) public onlyUnlocked returns(bool success) { require(_to != address(0)); require(balances[_from] >= _value); // Check if the sender has enough require(_value <= allowed[_from][msg.sender]); // Check if allowed is greater or equal balances[_from] -= _value; // Subtract from the sender balances[_to] += _value; // Add the same to the recipient allowed[_from][msg.sender] -= _value; // adjust allowed Transfer(_from, _to, _value); return true; } // @notice to query balance of account // @return _owner {address} address of user to query balance function balanceOf(address _owner) public view returns(uint balance) { return balances[_owner]; } /** * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender. * * Beware that changing an allowance with this method brings the risk that someone may use both the old * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards: * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729 * @param _spender The address which will spend the funds. * @param _value The amount of tokens to be spent. */ function approve(address _spender, uint _value) public returns(bool) { allowed[msg.sender][_spender] = _value; Approval(msg.sender, _spender, _value); return true; } // @notice to query of allowance of one user to the other // @param _owner {address} of the owner of the account // @param _spender {address} of the spender of the account // @return remaining {uint} amount of remaining allowance function allowance(address _owner, address _spender) public view returns(uint remaining) { return allowed[_owner][_spender]; } /** * approve should be called when allowed[_spender] == 0. To increment * allowed value is better to use this function to avoid 2 calls (and wait until * the first transaction is mined) * From MonolithDAO Token.sol */ function increaseApproval (address _spender, uint _addedValue) public returns (bool success) { allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue); Approval(msg.sender, _spender, allowed[msg.sender][_spender]); return true; } function decreaseApproval (address _spender, uint _subtractedValue) public returns (bool success) { uint oldValue = allowed[msg.sender][_spender]; if (_subtractedValue > oldValue) { allowed[msg.sender][_spender] = 0; } else { allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue); } Approval(msg.sender, _spender, allowed[msg.sender][_spender]); return true; } }

Solidity is a contract-oriented, high-level programming language for implementing smart contracts. Solidity is highly influenced by C++, Python and JavaScript and has been designed to target the Ethereum Virtual Machine (EVM).

Scenario : Implement a smart contract to transfer the property title from seller to buyer [Real Estate Industry]. 1. Write the below functions in solidity (40 points) NOTE: one address can have multiple lands A. Add new property : Parameters: Property Id, property value, property address, property owner address (eth address) Output: Mark Property Status as Pending , Property Id, property value, property address B. Buy a property (change the ownership): Prereq: Verify buyer and Seller are not same, Verify the status of the property Parameters: Property ID, new owner address Output: Mark new owner address as current address, change the status to sold C. Get all the property details of an address: Parameters: address Output: List all the properties that are not sold D. Get the property details using property ID and address: Parameters: PropertyID, address Output: Status, property value, property address E. Edit the property details: Parameters: PropertyID, changed values Output: Changes values