How to make a token code ERC20, Blockchain Ethereum, Pragma Solidity ^ 0.4.4;

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 HashnodeTestCoin is StandardToken { // 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 HashnodeTestCoin() {

        balances[msg.sender] = 1000000000000000000000;               // 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 = 1000000000000000000000;                        // Update total supply (1000 for example) (CHANGE THIS)

        name = "HashnodeTestCoin";                                   // Set the name for display purposes (CHANGE THIS)

        decimals = 18;                                               // Amount of decimals for display purposes (CHANGE THIS)

        symbol = "HTCN";                                             // Set the symbol for display purposes (CHANGE THIS)

        unitsOneEthCanBuy = 10;                                      // 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;

    }

}