The solution was in the previous video!
pragma solidity 0.7.5;
contract Bank {
mapping(address => uint) balance;
address owner;
event depositDone(uint amount, address indexed depositedTo);
constructor (){
owner = msg.sender;
}
modifier onlyOwner {
require(msg.sender == owner);
_;
}
function deposit() public payable returns (uint) {
balance[msg.sender] += msg.value;
emit depositDone(msg.value, msg.sender);
return balance [msg.sender];
}
function withdraw(uint amount) public returns (uint){
msg.sender.transfer(amount);
}
function getbalance() public view returns (uint){
return balance [msg.sender];
}
function transfer (address recipient, uint amount) public {
//check sender balance
require(balance[msg.sender] >= amount, "Balance not sufficient");
require(msg.sender != recipient, "Don't transfer money to yourself");
uint previousSenderBalance = balance[msg.sender];
_transfer (msg.sender, recipient, amount);
//event logs and further checks
assert(balance[msg.sender] == previousSenderBalance-amount);
}
function _transfer (address from, address to, uint amount) private {
balance[from] -= amount;
balance[to] += amount;
}
}