These are chat archives for ethereum/tutorials

Dec 2017
Dec 26 2017 08:05
Hi, when I put code from, to deploy crowdsale contracs, I see "No visibility specified. Defaulting to "public".
function transfer(address receiver, unit amount);
^-----------------------------------------------^". what's wrong?
Dec 26 2017 08:26
Hello,it will take weeks and weeks to sync...what is wrong?
Vidor Gencel
Dec 26 2017 11:37
@daur491 Nothing is wrong you can add the public modifier to the transfer interface and implementation like
function transfer(address receiver, unit amount) public;
Umar Abbas
Dec 26 2017 12:27
@daur491 put public before "{" of each function and it will start working
Dec 26 2017 19:19
Hi everyone ... Does anyone know if it is legal to lease the tokens that are sold, during the pre-ICO? Doyou have to put the money in escrow?
Dec 26 2017 19:26
hey guys any ethereum develover here who could help me?
vedat duymaz
Dec 26 2017 21:46
bilenn varmı burda
vedat duymaz
Dec 26 2017 22:01

pragma solidity ^0.4.16;

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) public; }

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 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
function TokenERC20(
    uint256 initialSupply,
    string tokenName,
    string 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 != 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;
    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 {
    _transfer(msg.sender, _to, _value);

 * 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;
    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
Dec 26 2017 23:16
@winspiral I had same syncing problem with wallet provided for Download on site. It takes forever to sync (and it slows down my system making it unuseable). I wonder if there is a a good and reputable online Ethereum wallet? Anybody?
Dec 26 2017 23:51
I am new here
I would like to learn about how to launch my own ico, I have projects in line
any help?