simple-bank-account-contract.sol

pragma solidity ^0.5.0; 
contract SimpleBank {
   mapping (address => uint) private balances;
   address public owner;


   constructor() public {
       owner = msg.sender;
   }

   function deposit() public payable returns (uint256) {
       require((balances[msg.sender] + msg.value) >= balances[msg.sender]);
       balances[msg.sender] += msg.value;
       return balances[msg.sender];
   }


   function withdraw(uint256 withdrawAmount) public returns (uint256 remainingBal) {
       require(withdrawAmount <= balances[msg.sender]);
       balances[msg.sender] -= withdrawAmount;
       msg.sender.transfer(withdrawAmount);
       return balances[msg.sender];
   }


   function balance() constant public returns (uint256) {
       return balances[msg.sender];
   }
}