How to Create an ERC20 Token?

#LETAK KODE IKLAN DISINI

ERC20 Tokens

How to make your own Ethereum-based ERC20 Token and launch ICO

Lately, I have been digging into blockchain and decentralized applications to educate myself and improve my knowledge. To make the learning process enjoyable, I decided to build my own Ethereum-based token and understand the ICO (Initial Coin Offering) launch process.

This article aims to give you an idea of how smart contracts work at Ethereum by launching a simple ICO demo.

Basics

Here are some basic terms that we will use in this article. If you are familiar with the following concepts, don't hesitate to move on to the next section.

• ERC20 tokens based on Ethereum: In Ethereum tokens represent tradable items such as coins, loyalty points, etc. You can make your own cryptocurrency based on Ethereum. Additionally, the benefit of following the ERC20 standard is that your token will be compatible with other clients or wallets that use the same standard.
• Smart Contracts: Smart Contracts are blocks of self-executed code used on the Ethereum blockchain. They contain data & function codes. Contracts make decisions, interact with other contracts, store data and transfer Ether (cryptocurrency units in the Ethereum blockchain) between users.
• Solidity: Language for writing smart contracts.
• MetaMask / Mist / MEW Wallet: A digital facility that stores your Ether and Ethereum-based tokens.

Now that you know the basic terminology used in this article, let's get started.

Step 1: Code

Open your favorite text editor and paste the following code:

pragma solidity ^0.4.4;

contract CCA {

    /// @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 StandardCCA is CCA {

    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 CoinCryptoAsia is StandardCCA { // CHANGE THIS. Update the contract name.

    /* Public variables of the token */

    /*
    NOTE:
    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 CoinCryptoAsia() {
        balances[msg.sender] = 1000000000000000000000000000;               // 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 = 1000000000000000000000000000;                        // Update total supply (1000 for example) (CHANGE THIS)
        name = "CoinCryptoAsia";                                   // Set the name for display purposes (CHANGE THIS)
        decimals = 18;                                               // Amount of decimals for display purposes (CHANGE THIS)
        symbol = "CCA";                                             // Set the symbol for display purposes (CHANGE THIS)
        unitsOneEthCanBuy = 1000;                                      // 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
        fundsWallet.transfer(msg.value);                               
    }

    /* 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;
    }
}

If the code is not effective, please click here!

The code above uses the Solidity language to build a simple ERC20 token. This code is well commented on and very easy to understand. After you paste the code into your text editor, look for the text: "REPLACE THIS". This is what you need to change based on the characteristics of your token. In the example above, I have named my token CoinCryptoAsia (CCA). Total supply is limited to 1000, but people can have at least 0.000000000000000001 because of 18 decimal places. In addition, the contract owner (the person who executes it) gets all the initial tokens. I have set the ICO price as follows:

1 ETH = CCA 1.000

This means, if someone sends 1 ETH to this smart contract, they will get 1.000 units.

Step 2:

For the next step you can visit the site link below. If you have questions about the ERC20 token code, leave a message in the comment column below.

How To Created ERC20 Token? Step 2