Token¶

1 Copy the exercise over to remix.¶

2 Compile and deploy the contract. Confirm variables and methods are available.¶

3 Update the contract metadata to be your own! Line 8 & 9.¶

string public constant symbol = 'YOUR NAME';
string public constant name = 'YOUR NAME Token';

4 Specify the rate for the purchase of your token, line 14¶

uint public constant rate_ = 2;  // rate of token / wei for purchase

5 Complete the buy method.¶

May purchase only with > 0 ETH, line 46
require(msg.value > 0, 'Cannot buy with a value of <= 0, Token.buy()');
Compute the amount of tokens to mint, line 49
uint256 tokenAmount = msg.value * rate_;
Update the total supply and the user’s balance, line 52 & 53
totalSupply_ += tokenAmount;   // NOTE overflow
balances_[msg.sender] += tokenAmount; // NOTE overflow
Finally emit events to notify the outside world, line 56 & 57
emit TokensMinted(msg.sender, msg.value, totalSupply_);
emit Transfer(address(0), msg.sender, msg.value);

6 Compile, deploy and confirm you can purchase your token. Confirm balance updated in `balances` mapping.¶

Video Tutorial [7-10][no audio]

7 Complete the transfer method.¶

Ensure from address has a sufficient balance, line 70
require(balances_[msg.sender] >= _value, 'Sender balance is insufficient, Token.transfer()');
Update the from and to balances, line 73 & 74
balances_[msg.sender] -= _value;  // NOTE underflow
balances_[_to] += _value;  // NOTE overflow
Finally emit an event of the transfer, line 77
emit Transfer(msg.sender, _to, _value);

8 Compile and deploy and confirm buy and transfer working.¶

9 Note error output if insufficient balance and other errors correct.¶

10 Usage¶

Purchase of tokens
Transfers

Important

But how can you get your hard earned ETH out of the contract that has been accumulating as tokens have been sold?!

11 Add a withdraw method, and claim the ETH sent to the contract! Line 102¶

Solution below…

Important

Save this contract to disk if you wish to use it again! However a completed token will be made available should you wish.

Solutions¶

Token Exercise Solution

11 Token Withdraw method

Confirm only the owner may withdraw, line 104

require(msg.sender == owner_, "only the owner may withdraw");

Transfer the balance of the contract(this) to the wallet, line 107

_wallet.transfer(address(this).balance);