Requiring expression in Solidity - ethereum

Question

So I have tried both of these in remix and one errors and the other does not and I'm trying to figure out why.
This is my first case -
mapping(address => uint) public balanceReceived;
function withdrawMoney(address _to, uint _amount) payable public {
require(balanceReceived[msg.sender] - _amount > 0, "You do not have the funds");
}
This produces the error -
transact to ExceptionExample.withdrawMoney errored: VM error: revert.
revert
The transaction has been reverted to the initial state.
Note: The called function should be payable if you send value and the value you send should be less than your current balance.
Debug the transaction to get more information.
However, the below works -
function withdrawMoney(address _to, uint _amount) payable public {
require(balanceReceived[msg.sender] > _amount, "You do not have the funds");
}
This produces the error -
transact to ExceptionExample.withdrawMoney errored: VM error: revert.
revert
The transaction has been reverted to the initial state.
Reason provided by the contract: "You do not have sufficient funds".
Debug the transaction to get more information.
In this case the require actually triggered.
I would expect both of these expressions to be identical, but the behaviour is different - why?

Answer 1

balanceReceived[msg.sender] - _amount
This subtraction in the first snippet causes an integer underflow if _amount is larger than balanceReceived[msg.sender].
Since Solidity 0.8.0, an exception is thrown if integer underflow or overflow would happen. And the uncaught exception results in the revert without any custom error message.
Solution: Use the second snippet, which can't cause integer underflow.
require(balanceReceived[msg.sender] > _amount, "You do not have the funds");
I'm not sure if this is on purpose, but it's unusual that your condition only allows the withdraw amount to be larger than the balance - not "larger or equal". So if you had balance of 1000000000000000000 (1 token with 18 decimals), you would only be able to withdraw 999999999999999999 (little less than the 1 full token) because of the current condition balanceReceived[msg.sender] > _amount.
If you changed the condition to "larger or equal" (balanceReceived[msg.sender] >= _amount), you would be able to withdraw the full balance.