/** *Submitted for verification at Etherscan.io on 2019-01-23 */ pragma solidity >=0.4.22 <0.6.0; contract owned { address public owner; constructor() public { owner = msg.sender; } modifier onlyOwner { require(msg.sender == owner); _; } function transferOwnership(address newOwner) onlyOwner public { owner = newOwner; } } interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes calldata _extraData) external; } contract TokenERC20 { // Public variables of the token string public name; string public symbol; uint8 public decimals = 18; // 18 decimals is the strongly suggested default, avoid changing it uint256 public totalSupply; // This creates an array with all balances mapping (address => uint256) public balanceOf; mapping (address => mapping (address => uint256)) public allowance; // This generates a public event on the blockchain that will notify clients event Transfer(address indexed from, address indexed to, uint256 value); // This generates a public event on the blockchain that will notify clients event Approval(address indexed _owner, address indexed _spender, uint256 _value); // This notifies clients about the amount burnt event Burn(address indexed from, uint256 value); /** * Constrctor function * * Initializes contract with initial supply tokens to the creator of the contract */ constructor( uint256 initialSupply, string memory tokenName, string memory tokenSymbol ) public { totalSupply = initialSupply * 10 ** uint256(decimals); // Update total supply with the decimal amount balanceOf[msg.sender] = totalSupply; // Give the creator all initial tokens name = tokenName; // Set the name for display purposes symbol = tokenSymbol; // Set the symbol for display purposes } /** * Internal transfer, only can be called by this contract */ function _transfer(address _from, address _to, uint _value) internal { // Prevent transfer to 0x0 address. Use burn() instead require(_to != address(0x0)); // Check if the sender has enough require(balanceOf[_from] >= _value); // Check for overflows require(balanceOf[_to] + _value > balanceOf[_to]); // Save this for an assertion in the future uint previousBalances = balanceOf[_from] + balanceOf[_to]; // Subtract from the sender balanceOf[_from] -= _value; // Add the same to the recipient balanceOf[_to] += _value; emit Transfer(_from, _to, _value); // Asserts are used to use static analysis to find bugs in your code. They should never fail assert(balanceOf[_from] + balanceOf[_to] == previousBalances); } /** * Transfer tokens * * Send `_value` tokens to `_to` from your account * * @param _to The address of the recipient * @param _value the amount to send */ function transfer(address _to, uint256 _value) public returns (bool success) { _transfer(msg.sender, _to, _value); return true; } /** * Transfer tokens from other address * * Send `_value` tokens to `_to` in behalf of `_from` * * @param _from The address of the sender * @param _to The address of the recipient * @param _value the amount to send */ function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) { require(_value <= allowance[_from][msg.sender]); // Check allowance allowance[_from][msg.sender] -= _value; _transfer(_from, _to, _value); return true; } /** * Set allowance for other address * * Allows `_spender` to spend no more than `_value` tokens in your behalf * * @param _spender The address authorized to spend * @param _value the max amount they can spend */ function approve(address _spender, uint256 _value) public returns (bool success) { allowance[msg.sender][_spender] = _value; emit Approval(msg.sender, _spender, _value); return true; } /** * Set allowance for other address and notify * * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the contract about it * * @param _spender The address authorized to spend * @param _value the max amount they can spend * @param _extraData some extra information to send to the approved contract */ function approveAndCall(address _spender, uint256 _value, bytes memory _extraData) public returns (bool success) { tokenRecipient spender = tokenRecipient(_spender); if (approve(_spender, _value)) { spender.receiveApproval(msg.sender, _value, address(this), _extraData); return true; } } /** * Destroy tokens * * Remove `_value` tokens from the system irreversibly * * @param _value the amount of money to burn */ function burn(uint256 _value) public returns (bool success) { require(balanceOf[msg.sender] >= _value); // Check if the sender has enough balanceOf[msg.sender] -= _value; // Subtract from the sender totalSupply -= _value; // Updates totalSupply emit Burn(msg.sender, _value); return true; } /** * Destroy tokens from other account * * Remove `_value` tokens from the system irreversibly on behalf of `_from`. * * @param _from the address of the sender * @param _value the amount of money to burn */ function burnFrom(address _from, uint256 _value) public returns (bool success) { require(balanceOf[_from] >= _value); // Check if the targeted balance is enough require(_value <= allowance[_from][msg.sender]); // Check allowance balanceOf[_from] -= _value; // Subtract from the targeted balance allowance[_from][msg.sender] -= _value; // Subtract from the sender's allowance totalSupply -= _value; // Update totalSupply emit Burn(_from, _value); return true; } } /******************************************/ /* ADVANCED TOKEN STARTS HERE */ /******************************************/ contract MyAdvancedToken is owned, TokenERC20 { uint256 public sellPrice; uint256 public buyPrice; mapping (address => bool) public frozenAccount; /* This generates a public event on the blockchain that will notify clients */ event FrozenFunds(address target, bool frozen); /* Initializes contract with initial supply tokens to the creator of the contract */ constructor( uint256 initialSupply, string memory tokenName, string memory tokenSymbol ) TokenERC20(initialSupply, tokenName, tokenSymbol) public {} /* Internal transfer, only can be called by this contract */ function _transfer(address _from, address _to, uint _value) internal { require (_to != address(0x0)); // Prevent transfer to 0x0 address. Use burn() instead require (balanceOf[_from] >= _value); // Check if the sender has enough require (balanceOf[_to] + _value >= balanceOf[_to]); // Check for overflows require(!frozenAccount[_from]); // Check if sender is frozen require(!frozenAccount[_to]); // Check if recipient is frozen balanceOf[_from] -= _value; // Subtract from the sender balanceOf[_to] += _value; // Add the same to the recipient emit Transfer(_from, _to, _value); } /// @notice Create `mintedAmount` tokens and send it to `target` /// @param target Address to receive the tokens /// @param mintedAmount the amount of tokens it will receive function mintToken(address target, uint256 mintedAmount) onlyOwner public { balanceOf[target] += mintedAmount; totalSupply += mintedAmount; emit Transfer(address(0), address(this), mintedAmount); emit Transfer(address(this), target, mintedAmount); } /// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens /// @param target Address to be frozen /// @param freeze either to freeze it or not function freezeAccount(address target, bool freeze) onlyOwner public { frozenAccount[target] = freeze; emit FrozenFunds(target, freeze); } /// @notice Allow users to buy tokens for `newBuyPrice` eth and sell tokens for `newSellPrice` eth /// @param newSellPrice Price the users can sell to the contract /// @param newBuyPrice Price users can buy from the contract function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner public { sellPrice = newSellPrice; buyPrice = newBuyPrice; } /// @notice Buy tokens from contract by sending ether function buy() payable public { uint amount = msg.value / buyPrice; // calculates the amount _transfer(address(this), msg.sender, amount); // makes the transfers } /// @notice Sell `amount` tokens to contract /// @param amount amount of tokens to be sold function sell(uint256 amount) public { address myAddress = address(this); require(myAddress.balance >= amount * sellPrice); // checks if the contract has enough ether to buy _transfer(msg.sender, address(this), amount); // makes the transfers msg.sender.transfer(amount * sellPrice); // sends ether to the seller. It's important to do this last to avoid recursion attacks } }