Fix transfers

[pm-coelho]

I was trying out the vulnerabilities shown in the article and found that on some transfers the balance was updated before the transfer was made:

balances[msg.sender] = 0;
msg.sender.transfer(balances[msg.sender]);

I think this solution might be better:

uint transferValue = balances[msg.sender];
balances[msg.sender] = 0;
msg.sender.transfer(transferValue);

Thank you so much for this article, I'm learning a lot from it.

[AgeManning]

Hey, thanks for catching these. I originally wrote them late at night, so I'm glad someone has corrected my mistakes. I caught one of these errors, recently but I'm glad you've found the rest.

I'm glad this article is helpful, that was its intention.

Thanks again for the PR :)