I am a new programmer, here is my code. Any useful information and tips are appreciated.

pragma solidity ^0.4.4;

contract Token {

    /// @return total amount of tokens
    function totalSupply() constant returns (uint256 supply) {}

    /// @param _owner The address from which the balance will be retrieved
    /// @return The balance
    function balanceOf(address _owner) constant returns (uint256 balance) {}

    /// @notice send `_value` token to `_to` from `msg.sender`
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transfer(address _to, uint256 _value) returns (bool success) {}

    /// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
    /// @param _from The address of the sender
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {}

    /// @notice `msg.sender` approves `_addr` to spend `_value` tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @param _value The amount of wei to be approved for transfer
    /// @return Whether the approval was successful or not
    function approve(address _spender, uint256 _value) returns (bool success) {}

    /// @param _owner The address of the account owning tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @return Amount of remaining tokens allowed to spent
    function allowance(address _owner, address _spender) constant returns (uint256 remaining) {}

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);


contract StandardToken is Token {

    function transfer(address _to, uint256 _value) returns (bool success) {
        //Default assumes totalSupply can't be over max (2^256 - 1).
        //If your token leaves out totalSupply and can issue more tokens as time goes on, you need to check if it doesn't wrap.
        //Replace the if with this one instead.
        //if (balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
        if (balances[msg.sender] >= _value && _value > 0) {
            balances[msg.sender] -= _value;
            balances[_to] += _value;
            Transfer(msg.sender, _to, _value);
            return true;
        } else { return false; }

    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        //same as above. Replace this line with the following if you want to protect against wrapping uints.
        //if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
        if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) {
            balances[_to] += _value;
            balances[_from] -= _value;
            allowed[_from][msg.sender] -= _value;
            Transfer(_from, _to, _value);
            return true;
        } else { return false; }

    function balanceOf(address _owner) constant returns (uint256 balance) {
        return balances[_owner];

    function approve(address _spender, uint256 _value) returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;

    function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
      return allowed[_owner][_spender];

    mapping (address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowed;
    uint256 public totalSupply;

contract FLOCK is StandardToken { // CHANGE THIS. Update the contract name.

    /* Public variables of the token */

    The following variables are OPTIONAL vanities. One does not have to include them.
    They allow one to customise the token contract & in no way influences the core functionality.
    Some wallets/interfaces might not even bother to look at this information.
    string public name;                   // Token Name
    uint8 public decimals;                // How many decimals to show. To be standard complicant keep it 18
    string public symbol;                 // An identifier: eg SBX, XPR etc..
    string public version = 'H1.0'; 
    uint256 public unitsOneEthCanBuy;     // How many units of your coin can be bought by 1 ETH?
    uint256 public totalEthInWei;         // WEI is the smallest unit of ETH (the equivalent of cent in USD or satoshi in BTC). We'll store the total ETH raised via our ICO here.  
    address public fundsWallet;           // Where should the raised ETH go?

    // This is a constructor function 
    // which means the following function name has to match the contract name declared above
    function FLOCK() {
        balances[msg.sender] = 10000000000;               // Give the creator all initial tokens. This is set to 1000 for example. If you want your initial tokens to be X and your decimal is 5, set this value to X * 100000. (CHANGE THIS)
        totalSupply = 10000000000;                        // Update total supply (1000 for example) (CHANGE THIS)
        name = "FLOCK";                                   // Set the name for display purposes (CHANGE THIS)
        decimals = 0;                                               // Amount of decimals for display purposes (CHANGE THIS)
        symbol = "FLK";                                             // Set the symbol for display purposes (CHANGE THIS)
        unitsOneEthCanBuy = 50000;                                      // Set the price of your token for the ICO (CHANGE THIS)
        fundsWallet = msg.sender;                                    // The owner of the contract gets ETH

    function() payable{
        totalEthInWei = totalEthInWei + msg.value;
        uint256 amount = msg.value * unitsOneEthCanBuy;
        require(balances[fundsWallet] >= amount);

        balances[fundsWallet] = balances[fundsWallet] - amount;
        balances[msg.sender] = balances[msg.sender] + amount;

        Transfer(fundsWallet, msg.sender, amount); // Broadcast a message to the blockchain

        //Transfer ether to fundsWallet

    /* Approves and then calls the receiving contract */
    function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);

        //call the receiveApproval function on the contract you want to be notified. This crafts the function signature manually so one doesn't have to include a contract in here just for this.
        //receiveApproval(address _from, uint256 _value, address _tokenContract, bytes _extraData)
        //it is assumed that when does this that the call *should* succeed, otherwise one would use vanilla approve instead.
        if(!_spender.call(bytes4(bytes32(sha3("receiveApproval(address,uint256,address,bytes)"))), msg.sender, _value, this, _extraData)) { throw; }
        return true;

1 Answer 1


Function to determine rate

Add code to return different values for the unitsOneEthCanBuy based on the block timestamp.


uint created = block.timestamp;
uint round_two = created + 7 days;
uint round_three = round_two + 30 days;
uint end = round_three + 30 days;

/// @notice Gets the conversion rate for ETH purchases.
/// @return Amount of tokens per ETH paid.
function unitsOneEthCanBuy() public view returns (uint _units) {
    if (block.timestamp > end) {
        return 0; // Sale has ended
    } else if (block.timestamp > round_three) {
        return 100000; // Round 3 price
    } else if (block.timestamp > round_two) {
        return 75000; // Round 2 price
    return 50000; // Round 1 price

Then you would remove:

uint256 public unitsOneEthCanBuy; 

And everywhere you use unitsOneEthCanBuy, use unitsOneEthCanBuy() instead.

Other potential issues

Overflow checking

You have very little code doing overflow checking in the transfer functions, you should probably use a common library like SafeMath to do the mathematical operations safely.


pragma solidity ^0.4.19;

import "github.com/OpenZeppelin/zeppelin-solidity/contracts/math/SafeMath.sol";

/// @title An example contract demonstrating using safe math operations
contract Example {
    using SafeMath for uint;

    /// @notice Adds two numbers together safely
    /// @param a The first number
    /// @param b The second number
    function addTogether(uint a, uint b) returns (uint) {
        return a.add(b);

ERC223 safety

Consider checking for contracts as transfer destinations and calling the tokenFallback method to make sure it's safe to transfer. This will stop your coins getting lost.


This is not enough to make your contract ERC223 compliant, but it's enough to ensure your tokens don't get lost

Add the following to your transfer and transferFrom functions just before you emit the Transfer events:

if (isContract(_to)) {
    iReceiver receiver = iReceiver(_to);
    receiver.tokenFallback(msg.sender, _value, empty);

Then add a function called isContract to your contract:

function isContract(address _addr) private view returns (bool _is_contract) {
    uint length;
    assembly {
        length := extcodesize(_addr)
    return (length>0);

And add an interface called iReceiver to above your contracts:

interface iReceiver {
    function tokenFallback(address _from, uint _value, bytes _data) external;
  • Hey if I could send you my revised code could you tell me if it looks better? I’d be glad to send you some ether for your time and help. Commented Mar 19, 2018 at 21:41
  • 1
    I appreciate your help, norganna. Commented Mar 19, 2018 at 21:41
  • Sure, post a link, I'm happy to review your final solution for upvotes :)
    – supakaity
    Commented Mar 19, 2018 at 21:56
  • collabedit.com/8btn8 Commented Mar 20, 2018 at 1:04
  • If this answered your question, please mark it as the correct answer. If not let me know so I can further assist.
    – supakaity
    Commented Apr 2, 2018 at 3:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.