Solidity lucks practic (1)

    pragma solidity ^0.4.19;
    contract Vuln{
    address public owner;
    string public name     = "Chain";
    string public symbol   = "CHA";
    uint8  public decimals = 18;
    uint public totalSupply=10000000000;
    bool  public isLoan=false;
    bool public solved;
    event  Approval(address indexed from, address indexed to, uint number);
    event  Transfer(address indexed from, address indexed to, uint number);
    event  Deposit(address indexed to, uint number);
    event  Withdrawal(address indexed from, uint number);
    
    mapping (address => u