- BusinessTrip is just another data type. We can use it just like int, double, string, etc.
// A central place to hold data.
BusinessTrip trip;- Business-trip-related constants can be pre-defined as static constants inside of a BusinessTrip. We can come up with their names, spell them in all capital letters and initialize them with values.
- We can access those static constants by just adding the prefix
BusinessTrip::to the field name that we want to read value from. - Static fields will be created only one time no matter how many BusinessTrip variables we make. Therefore, it is a perfect place for us to place configuaration for all the BusinessTrip.
// This is defined at the beginning of the program.
const double BusinessTrip::PRIVATE_CAR_MILAGE_ALLOWANCE = 0.27;
const double BusinessTrip::MAX_DAILY_PARKING_FEE = 6.00;
const double BusinessTrip::MAX_DAILY_TAXI_FEE = 10.00;
const double BusinessTrip::MAX_HOTEL_RATE_PER_NIGHT = 90.00;
const double BusinessTrip::MAX_DAILY_BREAKFAST = 9.00;
const double BusinessTrip::MAX_DAILY_LUNCH = 12.00;
const double BusinessTrip::MAX_DAILY_DINNER = 16.00;
//...
// We can read the value from a constant like this from anywhere in this program.
expenses = milesDriven * BusinessTrip::PRIVATE_CAR_MILAGE_ALLOWANCE;
- The set of variables that a BusinessTrip-type variable holds.
- We can access them by a dot notation after a BusinessTrip-type variable.
- Instance variables will be created for each instance of BusinessTrip. Therefore, individual trip data should be defined as instance variables.
trip.totalTripDays- Accepts the amount spent and the amount of the allowable.
- Adds those values to our in-memory central data storage.
// Add totalSpent and totalAllowable to our data storage.
trip.updateRecord(totalSpent, totalAllowable);==
For example, we can write the main as simple as this.
- Create a variable (of BusinessTrip type) that will store all the trip-related data.
- Pass the BusinessTrip-type variable to each function by reference. (NOTE: & required in the parameter lists of our input-blah-blah functions)
- Inside of each function, we prompt the user for required data, process it and write information into appropriate variables of the BusinessTrip-type variable by calling the trip.updateRecord(...) method.
- Print all the information.
int main() {
// 1.
BusinessTrip trip;
// 2. and 3.
inputDaysSpent(trip);
inputDepartureTime(trip);
inputReturnTime(trip);
inputAirfair(trip);
inputCarRental(trip);
inputPrivateVehicle(trip);
inputParking(trip);
inputTaxi(trip);
inputRegistration(trip);
inputHotel(trip);
inputMeals(trip);
// 4.
output(trip);
return 0;
}- This is a reusable function to ask the user for data of the specified data type, with the specified messages and the specified validation function.
- Using this, we do not type the same old prompt code again and again.
/**
* Prompts the user for data with the specified message and stores the data
* in the passed-in variable.
* @param data A variable in which the data will be stored.
* @param promtMsg A prompt message.
* @param errorMsg An error message.
* @param conditionFun A pointer to a function that accept a value of specified
* data type and returns bool.
*/
template <typename dataType>
void promptUser(dataType& data,
string promtMsg,
string errorMsg,
bool (*conditionFun)(dataType value)) {
bool isFinished = false;
while ( !isFinished ) {
cout << promtMsg << endl;
cout << ">>> ";
cin >> data;
// VALIDATION: 1. Input failure, 2. Invalid input.
if ( !cin || !conditionFun(data) ) {
cout << errorMsg << endl;
fixInputStream();
} else {
isFinished = true; // Exit the loop.
}
}
}Usage
/**
* Asks for the number of days spent on the trip.
* @param &trip A BusinessTrip object to which we write data.
*/
void inputDaysSpent(BusinessTrip& trip) {
promptUser<int>(
trip.totalTripDays, // a variable to which we write data
"How many days did you spent on this trip? ", // Prompt message
"Invalid trip days : Must be 1 or more", // Error message
oneOrGreater<int>); // Validation function
}
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