Reverting problem

[rileymross]

I'm following lesson 3 of the guide talking about when you send tokens to a smart contract, and how to get it to revert if not enough money is sent. But in my simulation, it doesn't seem to properly send the money back (to the original sender) when sending an invalid amount (below the minimum). Instead, the contract just keeps the money. In the guide it said to add the uint256 public number; line plus putting number=5; under the fundme function, but apart form showing me a "Number" button after deploying, it doesn't seem to actually do anything or undo the payment when I try sending an invalid payment.
I just want to know how to get it to undo payments that go below its minimum requested (reverting).

// SPDX-License-Identifier: MIT

//get funds from people
//withdraw funds
//set minimum usd value thanks to LINK

pragma solidity ^0.8.8;

contract FundMe {
    uint256 public number;
    function fund() public payable{
        number = 5;
        require(msg.value >= 1e18, "Sent a  amount!?"); // 1e18=10*18=1000000000000000000 - measured in terms of wei
    }

    //function withdraw(){}
}

[alymurtazamemon]

@rileymross

If you send the value less than the required then your amount will not deduct only the gas charges will be deducted from the account.

Suppose, in the require statement you need the value to be more than 1 ETH, and the total gas is 50000.

Now when you click the fundMe function with the value <= 1 ETH, then this value will not be deducted from the account, only the gas price from calling the function will deduct, let's say now the gas will be remaining 40000 (example) and revert back to account.

And like this example, if we have any computation (in this example, assigning a number a value of 5) then the gas cost for that also will be deducted.

Hope it clears your query, if so please mark it answered!

[rileymross]

So you still lose a bit of money due to the gas price not being refundable. That makes sense, and that mostly answers my question. But I'm still confused on the purpose of putting the computation into a value, which in this case was 5. What did that extra line change?

[alymurtazamemon]

@rileymross

In the real application, it matters a lot, because it changes the state of the blockchain that's why millions of other nodes have to update it as well and it cost lots of energy.

[alymurtazamemon]

That is the reason, reading from blockchain is free, but writing costs money. Because in reading other nodes do not have to update their data, you just have to read from the blockchain.