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The Smart Contract

Let's start with this basic Smart Contract. As mentioned before, it's written in Solidity 0.6, not the latest version, because of the integer roll-over example that we will demonstrate. 

//SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

contract ExceptionExample {

    mapping(address => uint) public balanceReceived;

    function receiveMoney() public payable {
        balanceReceived[msg.sender] += msg.value;
    }

    function withdrawMoney(address payable _to, uint _amount) public {
        if(_amount <= balanceReceived[msg.sender]) {
            balanceReceived[msg.sender] -= _amount;
            _to.transfer(_amount);
        }
    }
}

Add this Smart Contract to Remix. The correct Solidity Compiler Version should be selected automatically, but double check, to make sure everything is in order:

Okay, what does the Smart Contract do? It's a simplistic wallet contract.

  1. You can send Ether to the Smart Contract (via receiveMoney).
  2. You can withdraw Ether via withdrawMoney
  3. The Balance of your account is stored in the balanceReceived mapping.

So far so good. Pay attention to the withdrawMoney function. There is a if-else control structure. If you don't have enough balance, then simply nothing happens. That is not ideal, there is no user-feedback.

Let's give it a try!