What you are doing is printing the value in the array at spot [3][3], which is invalid for a 3by3 array, you need to loop over all the spots and print them.

for(int i = 0; i < 3; i++) {
    for(int j = 0; j < 3; j++) {
        printf("%d ", array[i][j]);
    }
    printf("\n");
} 

This will print it in the following format

10 23 42
1 654 0
40652 22 0

if you want more exact formatting you'll have to change how the printf is formatted.

The problem is that you are not keeping record of how many 'utilizadores' you are saving. Try this:

int records = 0; // we need this to keep track of how many records we have

case 1:
    a = introduzir_utilizador();
    fwrite(&a, sizeof(a), 1, fb);
    fclose(fb);
    records++; // we have one more record
    break;

and

case 2:
    // go though until the number of records has reached
    for(int i = 0; i != records; i++)
    {
        printf("%d %s %s %d",
               lista[i].user_id,
               lista[i].username,
               lista[i].password,
               lista[i].ano_nascimento);
        printf("\n");
    }

By doing this, you will only show valid elements of the 'lista'.

The same for:

while (fread(&a, sizeof(a), 1, fb) > 0)
    lista[i++] = a;

Keep track of how many 'utilizadores' you have read and add it to the record variable:

while (fread(&a, sizeof(a), 1, fb) > 0)
{
    lista[i++] = a;
    records++; // we've read another record
}

By the way, I can see that you plan to delete 'utilizadores'. Remember to decrease the count of 'records'.

You need to overload the <<operator for the Circle class as you need it (here you need to display the radius of the Circle object) As a parameter, you give it a Circle object.

In the class, I added the line :

friend std::ostream& operator<< (std::ostream &out, const Circle &matrix);

And outside the class its definition like this:

std::ostream& operator<< (std::ostream& out, const Circle& matrix)
{
    out << "Circle radius " << matrix.radius<<std::endl;
}

Then in the main function, your loop shall be modified to only give a Circle object like this:

for (int index = 0; index < size; index++)
{
      //cout << arr[index].Circle();  //Error: Invalid use of Circle::Circle
      cout << arr[index]; // no error as you defined operator <<for your Circle class
}

Here is you complete code modified

#include <iostream>

using namespace std;

class Circle
{
    private:
        double radius;
    public:
        Circle() //Constructor
        {   radius = 0; }

        Circle(double); //Parameterized Constructor

        void setRadius(double);

        double getRadius() const
        { return radius; }

        double getArea() const
        { return 3.14 * radius * radius; }

        friend std::ostream& operator<< (std::ostream &out, const Circle &matrix);

};

std::ostream& operator<< (std::ostream& out, const Circle& matrix)
{
    out << "Circle radius " << matrix.radius<<std::endl;
}

Circle::Circle(double r)
{
    radius = r;
}

void Circle::setRadius(double r)
{
    radius = r;
}

int main()
{
    int size = 3;  //Set size of array of objects
    Circle arr[size] = { Circle(1.2), Circle(2.2), Circle(5.5) }; //Array of Objects

    for (int index = 0; index < size; index++)
    {
      //cout << arr[index].Circle();  //Error: Invalid use of Circle::Circle
      cout << arr[index]; // no error as you defined operator <<for your Circle class    
   }

    Circle b(2.8);                  //Instance of class
    cout << b.getRadius();          //Prints out the radius of object

    Circle c;                       //Another instance
    cout << endl << c.getRadius(); //Another radius

    double r;                     //Variable to store the radius based on user input
    cout << "\nEnter a radius: ";
    cin >> r;
    c.setRadius(r);             //Pass user input into radius member function
    cout << c.getRadius();      //Print new radius of object c
    cout << endl << c.getArea(); //Prints area of object c.


    return 0;

}

The output is:

Circle radius 1.2
Circle radius 2.2
Circle radius 5.5
2.8
0
Enter a radius: 5
5
78.5

In your class, you need to provide a method for the description selector. This will return an NSString* of the contents of your class, formatted as you wish.

For example:

-(NSString*)description
{
   NSString* str1 = [NSString stringWithFormat:@"Purchase Share Price = %f",currentSharePrice];
   NSString* str2 = [NSString stringWithFormat:@"Current Share Price = %f",currentSharePrice];
   ... // do the rest of the items
   NSArray* strings =[NSArray arrayWithObjects:str1,str2,<the rest of them>, nil]
   NSString* result = [strings componentsJoinedByString:@"\n"];
   return result;
}

And then:

NSLog("%@",bolsa);

NOTE: This is a good approach whenever you need to debug/log objects in objective-c...having a method to convert complex objects into simple representations (i.e. a string) can be really helpful. Coding skill is not just knowing about functions and templates...its also about techniques and tools.

That is the memory address of the array (because of array-to-pointer decaying).

To correctly print pointers though, you should use %p.