Ether bank mini project..

banker.sol

pragma solidity 0.8.1;

contract Bank {
    
    mapping(address => uint) balance;
    
    function addBalance(uint _toAdd) public returns (uint) {
        
        balance[msg.sender] += _toAdd;
        
        return balance[msg.sender];  
    }
    
    function getBalance () public view returns (uint ){
        
        return balance[msg.sender];
    }
    
    function transfer ( address recipient, uint amount) public {
        require (balance[msg.sender] >= amount, "balance not sufficient!");
        require (msg.sender != recipient, "Don't tranfer money to yourself!");
        _transfer(msg.sender, recipient, amount);
        assert(balance[msg.sender] == previousSenderBalance - amount);
        
        //event logs and further checks.
        
    //     balance[msg.sender] -= amount;
    //     balance[recpient] += amount;
    }
    
    function _transfer(address from, address to, uint amount) private {
        
        balance[from] -= amount;
        balance[to] += amount;
        
    }
        
    }