Question

Write a full class definition for a class named GasTank , and containing the following members:
A data member named amount of type double.
A constructor that no parameters. The constructor initializes the data member amount to 0.
A function named addGas that accepts a parameter of type double . The value of the amount instance variable is increased by the value of the parameter.
A function named useGas that accepts a parameter of type double . The value of the amount data member is decreased by the value of the parameter. However, if the valueof amount is decreased below 0 , amount is set to 0 .
A function named isEmpty that accepts no parameters and returns a boolean value. isEmpty returns a boolean value: true if the value of amount is less than 0.1 , andfalse otherwise.
A function named getGasLevel that accepts no parameters. getGasLevel returns the value of the amount data member.

class GasTank
{
private:
double amount;
public:
GasTank();
void addGas(double);
void useGas(double);
bool isEmpty();
double getGasLevel();
};
GasTank::GasTank(){amount = 0;}
void GasTank::addGas(double a){amount += a;}
void GasTank::useGas(double a){amount -= a; if (amount < 0) amount = 0; }

bool GasTank::isEmpty(){if(amount < .1) return true; else return false;}
double GasTank::getGasLevel() {return amount;}

Answer 1

You listed both the class declaration and its function implementations. What part of code is in the header file, and what part of it is in theimplementation file?

Also, recall that for a class the default visibility is private. Therefore, all your functions are private -- including the constructor! -- so youcan't instantiate an object of the class. Try changing the visibility of the relevant functions to public.

Make sure the function signatures in the class declaration and the class definition match. So, if you declare

class GasTank {
// ...
public:
void addGas(double);
// ...
};
make sure you define

void GasTank::addGas(double d)
{
// ...
}
and not

double GasTank::addGas(double d)
{
// ...
}