C++ passing variables in classes and getting logical errors - c++

Question

Here is the prompt I haven't gotten to all of it yet though:
Implement a class named GasPump that will be used to model a pump at a gas station.
A GasPump object should be able to perform the following tasks:
- Display the amount of gas dispensed
- Display the total amount charged for the amount of gas dispensed
- Set the cost per gallon on gas
- Display the cost per gallon of gas
- Reset the amount of gas dispensed and amount charged before each new usage
- Keep track of the amount of gas dispensed and the total charge
When implementing the GasPump class , you should assume that the gas pump dispenses
.10 gallons of gas per second. Write a test program in main() that prompts the user
to enter the cost per gallon of gas and how many seconds they want to pump gas for.
Then, display the number of gallons of gas pumped, the cost per gallon of gas, and
the total cost of the gas.
I am having problems calculating the amount paid and keep getting logical errors. As this code stands it will compile but it gives garbage for a calculation for amount charged.
#include <iostream>
#include <iomanip>
using namespace std;
class GasPump{
public:
void setCostPerGallon(double cpg){
costPerGallon = cpg;
}
double getCostPerGallon(){
return costPerGallon;
}
void setAmountDispensed(int seconds){
const double dispense = 0.10;
sec = seconds;
amountDispensed = dispense * sec;
}
int getAmountDispensed(){
return amountDispensed;
}
//here is the function I am having problems with, at least I think.
void setAmountCharged(double costPerGallon, double amountDispensed){
amountCharged = costPerGallon * amountDispensed;
}
double getAmountCharged(){
return amountCharged;
}
private:
double costPerGallon;
int sec;
double amountCharged, amountDispensed;
};
int main() {
double cpg = 0.0;
int seconds = 0;
GasPump pump;
cout << "Enter the cost per gallon of gas:";
cin >> cpg;
while(cpg <= 0.0) {
cout << "Enter a value greater than 0:";
cin >> cpg;
}
pump.setCostPerGallon(cpg);
cout << "Enter the amount of seconds you want to pump gas for:";
cin >> seconds;
while(seconds <= 0.0) {
cout << "Enter a value greater than 0:";
cin >> seconds;
}
pump.setAmountDispensed(seconds);
cout << "The gas pump dispensed " << pump.getAmountDispensed() << " gallons of gas." << endl
<< "At $" << pump.getCostPerGallon() << " per gallon, your total is $"
<< fixed << setprecision(2) << pump.getAmountCharged() << "." << endl;
return 0;

Answer 1

You never call pump.setAmountCharged(...), so the member variable amountCharged is whatever the compiler decided to initialize it to when you instantiated pump (typically 0);
To fix this, either get rid of the member variable amountCharged and do the calculation for the amount when getAmountCharged is called, or call setAmountCharged appropriately before calling getAmountCharged.
Here's the first solution:
class GasPump {
...
double getAmountCharged() {
return costPerGallon * amountDispensed;
}
...
};