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Im writing a project and its for a car lot and im creating classes. I need to fullfill certain requirements. For accessory descriptions I need to use a pointer to a string that can be used to dynamically allocate an array of strings with the exact number of accessories. Each element will hold the name of the accessory.

If the number of accessories is 0, there is no need to allocate space, set the pointer to null.

And also pointer to a double that can eb used to dynamically allocate an array of doubles with the same number of elements as accessories. Each element will hold the cost of the associated accessory, that is, the cost in element 0 is the cost of the accessory in element 0. If the number of accessories is zero, set the pointer to null since there is no need to allocate space.

Heres what my class is so far without those last two requirements. Im stumped.

#ifndef VEHICLE_H

#define VEHICLE_H

class Vehicle

{
    public:
        Vehicle();

    protected:
        int vin_number;
        string manufacturer;
        string model;
        string color;
        double basecost;
        int accessories;
        string accessory_list;


    private:
};

#endif // VEHICLE_H

Please help it's an online course and ive been googling and reading for hours.

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6
  • YA i kinda just started trying to figure out if i was gonna use a char[] then declare a pointer to it or how i can do it. I just ook an unfinished screenshot kinda Commented May 10, 2013 at 5:50
  • I just don't know how to go about doing it. I know i can use the new operator and try but it's an online course and there's no one i can ask for help to show me how I would go about making the proper variable and loop function to do that. Commented May 10, 2013 at 5:52
  • does it solve your requirements if you make a vector<string> accessories; and use it as accessories.push_back("sun roof"); // ? Commented May 10, 2013 at 5:53
  • I can't use vectors of course :/ Commented May 10, 2013 at 5:54
  • 1
    @jimmyb online course tells you to avoid using parts of C++ ? Sound more like a terrible real life course. Commented May 10, 2013 at 5:55

2 Answers 2

Reset to default
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You should not dynamically allocate an array of string.

If you decide to use C++, you should be using STL and collections. Like this:

std::list<std::string> accessory_list;

If you decide to use C, a dynamically allocated string list could look like this:

//init
int accessory_count = 0;
int accessory_cap = 20;
char** accessory_list = calloc (sizeof(char*), accessorry_cap);

//add:
if (accessory_count==accessory_cap) {
  accessory_cap += 20;
  accessory_list = realloc (accessory_list, sizeof(char*)* accessorry_cap);
}
accessory_list[accessory_count++] = new_accessory.

If you really need a dynamic array of strings, you can do:

int accessory_arr_cap = 20;
string* accessory_arr = new string[accessory_arr_cap];

But since there is no realloc possible in this case, you will have to copy the entire array into new one if you need to enlarge it.

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3 Comments

there is no "List" in C++, perhaps you mean std::list, or rather, std::vector
Ya i know but thats what the project requirement is :/
@jimmyb I extended the answer. See new operator reference so that you really know what you are doing
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If the cost and name of the option are related, put them in a struct:

struct Option
{
    char* Name;
    double price;
}

Than what you are looking for is a collection, perhaps a std::vector<Option>. I'll leave it up to you to google the std::vector, it's a good learning exercise.

On a side note, do you have to use C++? You might find another language like C#, or Java a little easier to learn to program with.

If you can't use vectors, make your own collection. I won't post the code because I sense this is an assignment but here's how they normally work:

  • instantiate with a default size array of say 10.
  • keep a variable with this max in it
  • keep a variable with the current number of items in it (starts at 0, maybe call it count or something)
  • when you add a pointer, put it in element 'count' and increment the counter
    • if count = capacity then allocate a new array 2*capacity, copy all elements into it, delete the old one and assign the new array to the variable that was the old array.
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1 Comment

Sorry wrote this before you commented that you couldn't use vectors. Will update.

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