C++ Airfare Charge Calculation project - c++

Question

I have to create a program to calculate charges for airfare. It's a simple program so far and I am not done adding to it, but every time I run it the result turns out to be 0. Is there something missing in my code? I am a beginner and I would appreciate any advice on improving my code. Thank you.
#include <iostream>
using namespace std;
void main () {
int distance = 0;
int num_bags= 0;
int num_meals= 0;
double distance_price = distance * 0.15;
double bag_price = num_bags * 25.00;
double meal_price = num_meals * 10.00;
double total_airfare = 0.00;
cout << "CorsairAir Fare Calculator" << endl;
cout << "Enter the distance being travelled: " << endl;
cin >> distance;
cout << "Enter number of bags checked: " <<endl;
cin >> num_bags;
cout << "Enter the number of meals ordered: " << endl;
cin >> num_meals;
total_airfare = (distance_price + bag_price + meal_price);
cout << total_airfare;
}

Answer 1

Your confusion is completely understandable - the piece you're missing is that when you assign a variable, you're assigning the left side to the result of the right side at that moment in time. It's not like algebra, where you say f(x) = x + 5 and f(x) is always whatever x + 5 is.
So, you assign double distance_price = distance * 0.15 when distance is 0 (which you just initialized). distance_price remains 0 even after you ask for input and change distance.
Do your price calculations after you ask for input, and everything will work just fine.

Answer 2

You are calculating the distance_price bag_price meal_price with default values i.e. 0 not with the value which you took from user.
Below code works fine and you won't see the issue.
#include <iostream>
using namespace std;
// My compiler did not allow void main so used int main
int main () {
int distance = 0;
int num_bags= 0;
int num_meals= 0;
double distance_price ;
double bag_price ;
double meal_price;
double total_airfare;
cout << "CorsairAir Fare Calculator" << endl;
cout << "Enter the distance being travelled: " << endl;
cin >> distance;
cout << "Enter number of bags checked: " <<endl;
cin >> num_bags;
cout << "Enter the number of meals ordered: " << endl;
cin >> num_meals;
distance_price = distance * 0.15;
bag_price = num_bags * 25.00;
meal_price = num_meals * 10.00;
total_airfare = 0.00;
total_airfare = distance_price + bag_price + meal_price;
cout << total_airfare;
return 0;
}
Result
CorsairAir Fare Calculator
Enter the distance being travelled:
200
Enter number of bags checked:
2
Enter the number of meals ordered:
2
100