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I got it why we need decimals in ERC20s. But the thing I can't get it: When we are using transfer() method, should we write amount in wei (for ERC20s decimals count) or just integere. For example:

If we have a token with 3 decimals. I mint 100 of that token with mint(msg.sender, 100 * 10 ** 3). For transfer 5 tokens:

  1. transfer(_to, 5)
  2. transfer(_to, 5 * 10 ** 3)

Which one is true?

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The second one is true.

You can check the OpenZeppelin implementation here.

  * For example, if `decimals` equals `2`, a balance of `505` tokens should
  * be displayed to a user as `5.05` (`505 / 10 ** 2`).

All computations are done on integers representing the value * 10 ** n_decimals. This is to avoid using floating point, rounding errors and so on...

So with 3 decimals :

To transfer 5 (displayed) tokens, you need to transfer 5 * 10 ** 3 tokens internally. Think of it as working with cents, thousandths or more inside your smart contract.

Just as if you were to transfer 1 ETH, you'd actually be transfering a value of 1000000000000000000 (Wei), or 10 ** 18 Wei, as ETH has 18 decimals.

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  • Thanks! It is more clear now. Oct 31 '21 at 10:25

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