Which of the following function declaration is/are incorrect?

#include<iostream.h> 
class CuriousTab
{
    int x, y; 
    public:
    void SetValue(int &a, int &b)
    {
        a = 100;
        x = a;
        y = b;
        Display();
    }
    void Display()
    {
        cout<< x << " " << y; 
    }
};
int main()
{
    int x = 10;
    CuriousTab objCuriousTab;
    objCuriousTab.SetValue(x, x);
    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> 
class CuriousTab
{
    public: 
    int x, y;
    CuriousTab(int xx = 10, int yy = 20)
    {
        x = xx;
        y = yy; 
    }
    void Exchange(int *, int *);
};
int main()
{
    CuriousTab objA(30, 40); 
    CuriousTab objB(50); 
    objA.Exchange(&objA.x, &objB.y); 
    cout<< objA.x << " " << objB.y << endl; 
    return 0;
}
void CuriousTab::Exchange(int *x, int *y)
{
    int t;
    t  = *x;
    *x = *y;
    *y = t ; 
}

#include<iostream.h>
const double CuriousTabConstant(const int, const int = 0);
int main()
{
    const int c = 2 ;
    cout<< CuriousTabConstant(c, 10)<< " "; 
    cout<< CuriousTabConstant(c, 20)<< endl; 
    return 0;
}
const double CuriousTabConstant(const int x, const int y)
{
    return( (y + (y * x) * x % y) * 0.2);
}