Class inside another class

[brazyuri86]

Guys, how can I instantiate a class inside another class? I tried the normal way and did not work.

class listaSequencial
{
    public:

        // Criar a lista vazia de tamanho n
        bool criarLista(int n)
        {
            int lista[n];
            return true;
        }
        
        // Chamar método para adicionar um elemento
        void adicionar(int elemento)
        {
            l.adicionar(lista,elemento);
        }
        
    private:
        Lista l;
};

class Lista
{
    public:
        // Construtor para inicializacao do atributo qtdElementos
        Lista()
        {
            qtdElementos = 0;
        }
        
        // Adicionar um elemento ao final da lista
        void adicionar(int lista[], int elemento)
        {
            lista[qtdElementos++] = elemento;
        }
    private:
        int qtdElementos;
};

The error message:

19 `Lista' does not name a type
In member function `void listaSequencial::adicionar(int)':
15 `l' undeclared (first use this function)
(Each undeclared identifier is reported only once for each function it appears in.)
15 `lista' undeclared (first use this function)

[PanGalactic]

You do not show the error messages. What are they?

If you define List before mytest, does that work?

[brazyuri86]

Ok, now I post the real code and the error message.

In the line 19 I try to inicializate the other class Lista, but the sintax is wrong. What is the correct mode of this declaration?

Thanks.

[Galik]

You need to move class Lista to appear before listaSequencial.

[brazyuri86]

Ok, thanks, it seems that it worked. But now I have another question, typical beginner. I want to create a array, inside the class dynamically. The method criarLista do it to me with int lista[n]; but the function below, void adicionar(int elemento), when I try to use the array created l.adicionar(lista,elemento); returns me an error saying `list 'undeclared (first use this function).

How can I solve this problem?

Thanks again.

The last version of the code:

class Lista
{
    public:
        // Construtor para inicializacao do atributo qtdElementos
        Lista()
        {
            qtdElementos = 0;
        }
        
        // Adicionar um elemento ao final da lista
        void adicionar(int lista[], int elemento)
        {
            lista[qtdElementos++] = elemento;
        }
    private:
        int qtdElementos;
};

class listaSequencial
{
    public:
        
        // Criar a lista vazia de tamanho n
        bool criarLista(int n)
        {
            int lista[n];
            return true;
        }
        
        // Chamar método para adicionar um elemento
        void adicionar(int elemento)
        {
            l.adicionar(lista,elemento);
        }
        
    private:
        Lista l;
};

[filipe]

When you say:

        bool criarLista(int n)
        {
            int lista[n];
            return true;
        }

You're just creating an array of size n and letting the scope destroy it. You need to keep the array as a data member.

Also, watch out for this:

lista[qtdElementos++] = elemento;

Postfix increment returns the previous value, not the incremented value. You also need to make sure you won't write past the end of the array.

PS: eu sugiro programar sempre em inglês; os termos em português só causam confusão e tornam o programa mais difícil de ler.

[brazyuri86]

But I can't declare a array as a data member because I don't know - yet - the array length.
What is the solution? Understand the logic of my program?

A more general question. How to make a list then? I am studying data structure and want to make a list of some common operations such as add, delete and get information and to verify whether the same is empty or full, among others.

But this is very difficult in C++ for me yet ...

Thanks.

[Zhuge]

Make a pointer and use new to allocate the size.

[brazyuri86]

How???

class Lista
{
    public:
        // Construtor para inicializacao do atributo qtdElementos
        Lista()
        {
            qtdElementos = 0;
        }
        
        // Adicionar um elemento ao final da lista
        void adicionar(int lista[], int elemento)
        {
            lista[qtdElementos++] = elemento;
        }
    private:
        int qtdElementos;
};

class listaSequencial
{
    public:
        
        // Criar a lista vazia de tamanho n
        bool criarLista(int n)
        {
            lista(n) = new int();
            return true;
        }
        
        // Chamar método para adicionar um elemento
        void adicionar(int elemento)
        {
            l.adicionar(lista,elemento);
        }
        
    private:
        Lista l;
        int * lista;
};

[Zhuge]

Use new int[n] instead of just new int. You'll need to delete[] lista in the destructor though.

[brazyuri86]

Yes!!!!!! It works!!!!!!!

Thank you very much!!!!!!