Mapping addresses

mapping.sol

pragma solidity ^0.4.25;

contract MappingAddress {
    
    mapping(address => uint256) public balance_by_id;
    
    function assignDni(uint256 _dni) public {
        balance_by_id[msg.sender] = _dni;
    }
    
    function getDni(address _address) public view returns(uint256) {
        return (uint256)(balance_by_id[_address]);
    }
}