ERC20, correct way of setting totalSupply

Question

whats the correct way of setting the totalSupply and why?

decimals = 18;
totalSupply = 10000

or

decimals = 18;
totalSupply = 10000 * (10 ** uint256(decimals));

Whats the correct way? What's the difference? What is (10 ** uint256(decimals)) actually doing?

Seems like the last option is the correct one, because if I dont use the second option, my tokens in Metamask connected to Ganache will show always 0 balance.

Also

10000 === 10000 * (10 ** uint256(decimals)) ?

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Also another question, how can I call the methods transfer or transferFrom with a decimal value, sending 2.5 tokens for example? How would that be done, since the type is uint and I cant pass decimals.

Answer 1

The second way is correct. In Solidity, ** is the exponentiation operator, so 10 ** 18 is the same as 10¹⁸. So this:

uint256 totalSupply = 10000 * (10 ** uint256(decimals));

Means the total supply will be 10,000 × 10¹⁸ tokens. We use 10ⁿ because Solidity doesn´t (fully) support decimal numbers, only integers. In wallets, dApps, etc. this number is converted back to the actual balance with decimals.

To specify 2.5 tokens, for example, you would use 2.5 × 10¹⁸ (= 2,500,000,000,000,000,000) instead. You can reverse it by multiplying with 10^-18 instead.