Question

I have a base class called Mijloc_transport and 2 derived classes called Masina and Tramvai. I must do an menu type program that can create different kind of objects from the derived classes and show them. I’m using the UPCASTING method and when I press 1 the if(tasta=="1") creates an object and I can see what type it is using: tabp[0]->show();. It seems that when the program enters again in the do loop (using the main label), the object created as 1 is destroyed and I can’t see tabp[0]->show(); because the reference is deleted. What shall I do to keep the objects alive so I can put them in tabp?

Masina b(30);
p=&b;
tabp[i]=p;

so later I can display them….10x for your help

#include "include.hpp"
#include <ctype.h>
#include <cstdlib>

int main(void)
{    

    int i=0;

    Mijloc_transport *tabp[MAX];
    Mijloc_transport *p;

    int tasta;
main:
    do
    {
        //cout<<"\n\n\n\n\n";
        cout<<endl<<"apasa orice tasta pentru a reveni la meniu "<<endl; getch();
        system("cls");
        cout<<"Tasteaza numarul optiunii dorite din meniu:"<<endl; 
        cout<<"1. creaza o masina cu 30 cai putere"<<endl;      //create an Masina derived Oject
        cout<<"2. creaza un tramvai cu 20 de locuri"<<endl;//create an Tramvai derived Oject
        cout<<"3. afiseaza memoria"<<endl;                       //print the objects
        cout<<"4. iesire"<<endl;
        tasta=cin.get();
    }
    while(tasta!='1' && tasta!='2'&& tasta!='3'&& tasta!='4');


    if(tasta=='1')
    {
        Masina b(30);
        p=&b;
        tabp[i]=p;

        tabp[0]->show();

        cout<<endl<<"apasa orice tasta pentru a reveni la meniu "<<endl;
        getch();

        //i++;            //TREBUIE INCREMENTAT cand ai mai mult de un obiect
        goto main;
    }

    if(tasta=='3')
    {
        //afiseaza elementele din memorie
        //for(int j=0;j<=i;j++)                      //J<=i
        //tabp[j]->show();

        tabp[0]->show();
        cout<<endl<<"apasa orice tasta pentru a reveni la meniu "<<endl;
        getch();

        return 1;
    }
}

Answer 1

Instead of:

Masina b(30);
p=&b;
tabp[i]=p;

do:

tabp[i] = new Masina(30);

and do not forget to do:

for ( unsigned int i = 0; i < MAX; ++i )
{
    delete tabp[i];
}

When you no longer need tabp (before existing main).