TokenERC20 | ERC20 Standart Token | Cryptocurrency library

oh, I finally got it and share it. it looks like it's about javascript vm problem, because I tested on Javascript VM in remix. I think it's sort of memory problem of vm. I checked this code worked on rinkeby testnet well.

This interface is just for convenience, so you can easily call the interface methods. You can cast any smart contract address to this interface, even if they are not an instance of this interface.

For instance, if I would make the following changes to your example:

ApproveAndCall.sol

The TokenERC20 is the standard ERC20 token that most people are using. This contract allows you to create a token that has the basic functionality of an ERC20 token, such as transfer, transferFrom, approve, etc. These are all required functions to qualify for the ERC20 standard.

The MyAdvancedToken contract is an extension of the TokenERC20 contract (hence the line, MyAdvancedToken is owned, TokenERC20). What this means is MyAdvancedToken is able to use all the functionality of TokenERC20 without rewriting the whole thing. The reason this contract exists is to give the token additional functionality.

In this example, you can see that the owner has the ability to mint additional tokens and to freeze tokens of a specific user. While this is not a part of the ERC20 specification directly, you are allowed to add functions like this.

You may see that some functions, such as _transfer are in both contracts. When this occurs, the child contract function overwrites the parent contract. In this case, the _transfer function that gets executed when called is the one that checks for frozen accounts.

You need to understand how the tokens works in general and what token actually is. Token is just a smart-contract which keeps information about balances (mapping address => uint). So it just keeps the amount of tokens held by specified address. Nothing more. Another thing you need to know is fallback function(the one without the name). In your case it is empty.

It's not multiplying by 10. It's multiplying by (10 ^ 18). That line is used to handle the decimal offset since fixed point numbers are not yet supported in Solidity.

An ERC20 token is not required to use 18 decimals (or any at all), but it's recommended to use some level of precision since the value of a token can fluctuate significantly. 18 is used in most examples because contracts that receive ether work with values at the wei level (1 ether = 10^18 wei).

1. Using > instead of >= is a typo and >= sign should be preferred over >. Imagine you have 15 tokens and want to send all of them - you'll not pass the require with > sign.

2. It is safe because no one can use once deployed contract to inherit from. To create malignant inheritance you need to use parent contract code in the same or different file and deploy it one more time, creating the second base contract, distinct from the first one and not able to take its tokens.