What is correct about the following program?

#include<iostream.h> 
class Base
{
    int x, y, z; 
    public: 
    Base()
    {
        x = y = z = 0;
    }
    Base(int xx, int yy = 'A', int zz = 'B')
    {
        x = xx;
        y = x + yy;
        z = x + y;
    }
    void Display(void)
    {
        cout<< x << " " << y << " " << z << endl;
    }
};
class Derived : public Base
{
    int x, y; 
    public:
    Derived(int xx = 65, int yy = 66) : Base(xx, yy)
    {
        y = xx; 
        x = yy;
    }
    void Display(void)
    {
        cout<< x << " " << y << " ";
        Display(); 
    }
};
int main()
{
    Derived objD;
    objD.Display();
    return 0; 
}

#include<iostream.h> 
struct CuriousTab
{
    int arr[5]; 
    public:
    void CuriousTabFunction(void);
    void Display(void);
};
void CuriousTab::Display(void)
{
    for(int i = 0; i < 5; i++) 
        cout<< arr[i] << " " ;
}
void CuriousTab::CuriousTabFunction(void)
{
    static int i = 0, j = 4; 
    int tmp = arr[i]; 
    arr[i]  = arr[j]; 
    arr[j]  = tmp   ; 
    i++;
    j--;
    if(j != i) CuriousTabFunction();
}
int main()
{
    CuriousTab objCuriousTab = {{ 5, 6, 3, 9, 0 }};
    objCuriousTab.CuriousTabFunction();
    objCuriousTab.Display();
    return 0; 
}

#include<iostream.h> 
struct CuriousTabArray
{
    int arr[5]; 
    public:
    void CuriousTabFunction();
    void Display();
};
void CuriousTabArray::CuriousTabFunction()
{
    static int i = 0, j = 4; 
    i++;
    j--;
    if(j > 0)
        CuriousTabFunction(); 
    int tmp = arr[i]; 
    arr[i]  = arr[j]; 
    arr[j]  = tmp; 
    i--;
    j++;
}
void CuriousTabArray::Display()
{
    for(int i = 0; i < 5; i++)
        cout<< arr[i] << " ";
} 
int main()
{
    CuriousTabArray objArr = {{5, 6, 3, 9, 0}};
    objArr.CuriousTabFunction();
    objArr.Display();
    return 0; 
}

#include<iostream.h> 
static double gDouble; 
static float  gFloat; 
static double gChar; 
static double gSum = 0; 
class BaseOne
{
    public:
    void Display(double x = 0.0, float y = 0.0, char z = 'A')
    {
        gDouble = x;
        gFloat  = y;
        gChar   = int(z);
        gSum    = gDouble + gFloat + gChar;
        cout << gSum; 
    }
};
class BaseTwo
{
    public: 
    void Display(int x = 1, float y = 0.0, char z = 'A')
    {
        gDouble = x;
        gFloat  = y;
        gChar   = int(z); 
        gSum    = gDouble + gFloat + gChar;
        cout << gSum;
    }
};
class Derived : public BaseOne, BaseTwo
{
    void Show()
    {
        cout << gSum;
    } 
}; 
int main()
{
    Derived objDev;
    objDev.BaseTwo::Display(10, 20, 'Z');
    return 0; 
}

#include<iostream.h> 
class CuriousTab
{ 
    public:
    void CuriousTab(int x = 15)
    {
        x = x/2; 
        if(x > 0)
            CuriousTab(); 
        else
            cout<< x % 2; 
    } 
};
int main()
{
    CuriousTab objIB;
    objIB.CuriousTab();
    return 0; 
}

#include<iostream.h>
#include<string.h> 
class CuriousTabString
{
    char x[50]; 
    char y[50]; 
    char z[50]; 
    public:
    CuriousTabString()
    { }
    CuriousTabString(char* xx)
    {
        strcpy(x, xx); 
        strcpy(y, xx);
    }
    CuriousTabString(char *xx, char *yy = " C++", char *zz = " Programming!")
    {
        strcpy(z, xx); 
        strcat(z, yy); 
        strcat(z, zz);
    } 
    void Display(void)
    {
    cout<< z << endl;
    } 
}; 
int main()
{
    CuriousTabString objStr("Learn", " Java");
    objStr.Display();
    return 0; 
}

#include<iostream.h> 
class CuriousTabSample
{
    private:
    int AdditionOne(int x, int y = 1) 
    {
        return x * y;
    }
     
    public:
    int AdditionTwo(int x, int y = 1)
    {
        return x / y;
    } 
}; 
int main()
{
    CuriousTabSample objCuriousTab;
    cout<<objCuriousTab.AdditionOne(4, 8)<<" "; 
    cout<<objCuriousTab.AdditionTwo(8, 8); 
    return 0;
}

#include<iostream.h> 
class CuriousTab
{
    static int x; 
    public:
    static void SetData(int xx)
    {
        this->x = xx; 
    }
    static void Display() 
    {
        cout<< x ;
    }
};
int CuriousTab::x = 0; 
int main()
{
    CuriousTab::SetData(22);
    CuriousTab::Display();
    return 0; 
}

#include<iostream.h> 
class India
{
    public:
    struct CuriousTab
    {
        int   x;
        float y;
        void Function(void)
        {
            y = x = (x = 4*4); 
            y = --y * y;
        }
        void Display()
        {
            cout<< y << endl;
        } 
    }B; 
}I; 
int main()
{
    I.B.Display(); 
    return 0;
}

#include<iostream.h>
#include<string.h> 
class CuriousTab
{
    int val; 
    public:
    void SetValue(char *str1, char *str2)
    {
        val = strcspn(str1, str2);
    }
    void ShowValue()
    {
        cout<< val;
    } 
};
int main() 
{
    CuriousTab objCuriousTab;
    objCuriousTab.SetValue((char*)"India", (char*)"CuriousTab"); 
    objCuriousTab.ShowValue(); 
    return 0; 
}

#include<iostream.h> 
class Point
{
    int x, y; 
    public:
    Point(int xx = 10, int yy = 20)
    {
        x = xx;
        y = yy; 
    }
    Point operator + (Point objPoint)
    {
        Point objTmp;
        objTmp.x = objPoint.x + this->x; 
        objTmp.y = objPoint.y + this->y;
        return objTmp;
    }
    void Display(void)
    {
        cout<< x << " " << y;
    }
};
int main()
{
    Point objP1;
    Point objP2(1, 2);
    Point objP3 = objP1 + objP2;
    objP3.Display(); 
    return 0; 
}