How to create objects using a variable.

Hello everyone.
I embarked on creating my first console application using classes.
I simplified my code but my problem boils down to creating multiple objects of a car class using input from the user using a variable. As soon as I create one object I can't seem to be able to access its members. In fact the code will not even compile. In contrast if I create an object by assigning specific identifier as in the second example everything works fine. Is there a way to access mpg member of a car object in the first example some other way?

class car{
public:
int mpg;
int max_speed;
};

example 1

int main(){
string i;
cin >> i;
car i;
i.mpg = 10;

system("PAUSE");
return 0;
}

example 2

int main(){
car bmw;
bmw.mpg = 10;

system("PAUSE");
return 0;
}

Last edited on

Yanson (622)

your car and string variables have the same name so how is the compiler supposed to tell them apart.

seweriusz (3)

Yes, you are right. I see that now.

Updated Question: is it possible to use a variable to create an object then?

I mean since I need to capture user input into a variable first and then use it to create the class object, I will always run into same issue. Any thoughts on that?

Thank you in advance.

Last edited on

EssGeEich (2305)

No, you cannot.
Well, you COULD. But it takes a lot of work.

seweriusz (3)

OK, then I need to rethink my program.

So what exactly happens if I do repeat declaration of a bmw car object. Do I have two instances of bmw? And if yes how would I differentiate between their members? Or is this also not allowed?

class car{
public:
int mpg;
int max_speed;
};

int main(){
car bmw;
car bmw;

system("PAUSE");
return 0;
}

Last edited on

EssGeEich (2305)

You can't do that - not in the same scope.
This is possible instead:

car bmw; // a
    {
    car bmw; // b, now overrides a
    bmw.i=0; // b.i
    } // b is destroyed, a is restored
bmw.i=0; // a.i

But you should consider using different names.

car BmwM3;
car BmwM5;
car FordMustang;
car FordFiesta;

Tell me what do you want to achieve - there could be another way.
It's 9 entire minutes I'm trying to send this message. F'ing hell.

mobotus (251)

You could always do an array of car objects.

class car{
public:
	std::string name;
	int mpg;
	int max_speed;
};


int main(){
	
	int num;
	std::string name;
	car* ptr;

	std::cout << "Number of cars: ";
	std::cin >> num;

	ptr = new car[num];

	for (int i = 0; i < num; i++){
		std::cout << "Enter name of car " << i + 1 << ": ";
		std::cin >> name;
		std::cout << std::endl;
		ptr[i].name = name;
	}

	delete[] ptr;
	return 0;
}

Last edited on

TheIdeasMan (2981)

Hi,

A couple of other ideas:

1. Provide a member variable which is the name of the object:

class car{
public:
std::string m_Make;
std::string m_Model;
int m_mpg;
int m_max_speed;
};

Although member variables should be private: You could use a struct (public by default), but make the object (or a collection of them )a private member of the another class.

2. Have a container of like objects:

1
2

std::vector<car> BMWCollection;
std::vector<car> FordCollection;

:+)

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How to create objects using a variable.

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