Inheritance doesn't work when using loop - c++

Question

I have a small problem with inheritance in my code - it suddenly stops working when I add identical code in another "if" statement in my loop.
Here is the code I use for "main.cpp":
#include "bibl.h"
using namespace std;
int main()
{
int o;
Vec2 test;
while(1)
{
cout<<"1. Add item and show."<<endl<<"2. Show."<<endl;
cin>>o;
if(o==1)
{
InhItem a("Test",100);
test.addItem(&a);
cout<<"This show works:"<<endl;
test.getVec1(0)->getItem(0)->Show();//This code works.
}
else if(o==2)
{
cout<<"This show doesn't work:"<<endl;
test.getVec1(0)->getItem(0)->Show();//This doesn't.
}
}
system("pause");
return 0;
}
And the code for "bibl.h":
#ifndef TEST1
#define TEST1
#include <iostream>
#include <vector>
#include <string>
using namespace std;
class Item
{
protected:
string im;
string theme;
public:
Item(string im=" ", string theme=" "):im(im),theme(theme)
{
}
~Item()
{
}
string getTheme()
{
return theme;
}
virtual void Show()
{
}
};
class InhItem:public Item
{
int tst;
public:
InhItem(string im=" ", int tst=0):Item(im),tst(tst)
{
}
~InhItem()
{
}
void Show()
{
cout<<tst<<endl;
}
};
class Vec1
{
vector<Item*> Vec1a;
string theme;
public:
Vec1(string theme=" "):theme(theme)
{
}
~Vec1()
{
}
void addToVec1a(Item *item)
{
Vec1a.push_back(item);
}
string getTheme()
{
return theme;
}
Item *getItem(int p)
{
return Vec1a[p];
}
};
class Vec2
{
vector<Vec1*> Vec2a;
public:
Vec2()
{
}
~Vec2()
{
}
void addToVec2(Vec1 *vec1)
{
Vec2a.push_back(vec1);
}
void addItem(Item *item)
{
for(int i=0;i<=Vec2a.size();i++)
{
if(i==Vec2a.size())
{
addToVec2(new Vec1(item->getTheme()));
Vec2a[i]->addToVec1a(item);
break;
}
else if(Vec2a[i]->getTheme().compare(item->getTheme())==0)
{
Vec2a[i]->addToVec1a(item);
break;
}
}
}
Vec1 *getVec1(int r)
{
return Vec2a[r];
}
};
#endif
When I try to use the 2nd "if" after adding the item with 1st, it doesn't show - in 1st "if" test.getVec1(0)->getItem(0)->Show(); works, but in another it doesn't.
What is the cause of this problem and how can I fix it?