Classes and Indexed Properties

We learned to create and use indexed properties that were taking parameters of primitive types. Just as we did with primitive types, you can create an indexed property that is of a class type. For example, you can create a class so that one of the its member variables declared as an array can be accessed with an index directly applied to an instance of the class.

1. Start Microsoft Visual C++ 2005 or Microsoft Visual C++ 2005 Express Edition
2. To start a new project, on the main menu, click File -> New -> Project...
3. In the Project Types, make sure Visual C++ is selected.
   In the Templates list, click CLR Empty Project
4. Set the name to PropertyRental2 and click OK
5. To create a new class, on the main menu, click Project -> Add Class...
6. In the Templates list, click C++ Class and click Acc
7. Set the Name to CRentalProperty and click Finish
8. Change the header file as follows:
    

   #pragma once using namespace System; public ref class CRentalProperty { private: long propCode; String ^ cond; short beds; double baths; double val; public: property long PropertyCode { long get() { return propCode; } void set(long value) { propCode = value; } } property String ^ PropertyCondition { String ^ get() { return cond; } void set(String ^ value) { cond = value; } } property short Bedrooms { short get() { return beds; } void set(short value) { beds = value; } } property double Bathrooms { double get() { return (baths <= 0) ? 0.00 : baths; } void set(double value) { baths = value; } } property double MonthlyRent { double get() { return (val <= 0) ? 0.00 : val; } void set(double value) { val = value; } } public: CRentalProperty(void); virtual String ^ ToString() override; };

9. Open the RentalProperty.cpp file and change it as follows:
    

   #include "RentalProperty.h" CRentalProperty::CRentalProperty(void) { Random ^ rnd = gcnew Random(); propCode = rnd->Next(100000, 999999); cond = L"Unknown"; beds = 0; baths = 0.0; val = 0.00; } String ^ CRentalProperty::ToString() { return L"Property #: " + PropertyCode + L"\nCondition: " + PropertyCondition + L"\nBedrooms: " + Bedrooms + L"\nBathrooms: " + Bathrooms + L"\nMonthly Rent: " + MonthlyRent.ToString("C"); };

10. To create a new class, on the main menu, click Project -> Add Class...
11. In the Templates list, make sure C++ Class is selected and click Add
12. Set the Name to CPropertyListing and press Enter
13. Change the header file as follows:
     

    #pragma once #include "RentalProperty.h" public ref class CPropertyListing { public: array<CRentalProperty ^> ^ props; property String ^ default[long] { String ^ get(long code) { for (int i = 0; i < props->Length; i++) if (code == props[i]->PropertyCode) return L"Property #: " + props[i]->PropertyCode + L"\nCondition: " + props[i]->PropertyCondition + L"\nBedrooms: " + props[i]->Bedrooms + L"\nBathrooms: " + props[i]->Bathrooms + L"\nMonthly Rent: " + props[i]->MonthlyRent.ToString("C"); return L"Unidentifiable Property"; } } public: CPropertyListing(void); };

14. Access the PropertyListing.cpp source file and change it as follows:
     

    #include "PropertyListing.h" CPropertyListing::CPropertyListing(void) { Random ^ rnd = gcnew Random; props = gcnew array<CRentalProperty ^>(40); // Create a few properties ready to be rented props[0] = gcnew CRentalProperty; props[0]->PropertyCode = rnd->Next(100000, 999999); props[0]->PropertyCondition = L"Excellent"; props[0]->Bedrooms = 5; props[0]->Bathrooms = 3.5; props[0]->MonthlyRent = 2650; props[1] = gcnew CRentalProperty; props[1]->PropertyCode = rnd->Next(100000, 999999); props[1]->PropertyCondition = L"Excellent"; props[1]->Bedrooms = 3; props[1]->Bathrooms = 2.5; props[1]->MonthlyRent = 1750; props[2] = gcnew CRentalProperty; props[2]->PropertyCode = rnd->Next(100000, 999999); props[2]->PropertyCondition = L"Good"; props[2]->Bedrooms = 4; props[2]->Bathrooms = 2.5; props[2]->MonthlyRent = 2450; props[3] = gcnew CRentalProperty; props[3]->PropertyCode = rnd->Next(100000, 999999); props[3]->PropertyCondition = L"Excellent"; props[3]->Bedrooms = 1; props[3]->Bathrooms = 1.0; props[3]->MonthlyRent = 880; props[4] = gcnew CRentalProperty; props[4]->PropertyCode = rnd->Next(100000, 999999); props[4]->PropertyCondition = L"Excellent"; props[4]->Bedrooms = 3; props[4]->Bathrooms = 2.5; props[4]->MonthlyRent = 1880; props[5] = gcnew CRentalProperty; props[5]->PropertyCode = rnd->Next(100000, 999999); props[5]->PropertyCondition = L"Good"; props[5]->Bedrooms = 2; props[5]->Bathrooms = 1.0; props[5]->MonthlyRent = 1050; // Since we don't yet have a complete list of properties // Create some empty ones for (int i = 6; i < 40; i++) { props[i] = gcnew CRentalProperty; } }

15. To create a new file, on the main menu, click Project -> Add New Item...
16. In the Templates list, click C++ File (.cpp)
17. Set the name to Exercise and click OK
18. Implement the file as follows:
     

    using namespace System; #include "PropertyListing.h" int main() { CPropertyListing ^ properties = gcnew CPropertyListing; long lngCode; Console::WriteLine(L"Here is a list of our properties by code"); for (int i = 0; i < 6; i++) Console::WriteLine(L"Property Code: {0}", properties->props[i]->PropertyCode); try { Console::Write("Enter Property Code: "); lngCode = long::Parse(Console::ReadLine()); Console::WriteLine(L"======================================"); Console::WriteLine(L"Property Information"); Console::WriteLine(L"--------------------------------------"); Console::WriteLine(properties[lngCode]); Console::WriteLine(L"======================================"); } catch(FormatException ^) { Console::WriteLine(L"=- Invalid Property Code -="); } return 0; }

19. Press Ctrl + F5 to execute the application. Here is an example:
     

    Here is a list of our properties by code Property Code: 355443 Property Code: 653004 Property Code: 800118 Property Code: 839375 Property Code: 148561 Property Code: 697001 Enter Property Code: 697001 ====================================== Property Information -------------------------------------- Property #: 697001 Condition: Good Bedrooms: 2 Bathrooms: 1 Monthly Rent: $1,050.00 ====================================== Press any key to continue . . .

20. Close the DOS window

Before designing an indexed property that is class-based, first create the class that will be used as the data type. The class can be simple or complex as you judge it necessary. Here is an example of a simple class:

public ref class CStudent
{
public:
    String ^ FirstName;
    String ^ LastName;
    int      Gender;
};

When creating the class that will host the indexed property, declare an array member variable for the class. Then, create the default property with the desired accessor(s). Here is an example:

public ref class CStudent
{
public:
    String ^ FirstName;
    String ^ LastName;
    int      Gender;
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ std;

public:
    property CStudent ^ default[int]
    {
        CStudent ^ get(int i) { return std[i]; }
    }

    CSchoolRegistration()
    {
	std = gcnew array<CStudent ^>(5);
    }
};

After creating the indexing class, you can use it and access the indexed property; for example, you can retrieve its value(s). Here is an example:

using namespace System;

public ref class CStudent
{
public:
    String ^ FirstName;
    String ^ LastName;
    int      Gender;
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ std;

public:
    property CStudent ^ default[int]
    {
        CStudent ^ get(int i) { return std[i]; }
    }

    CSchoolRegistration()
    {
	std = gcnew array<CStudent ^>(5);
	
        std[0] = gcnew CStudent;
        std[0]->FirstName = L"Alfredo";
        std[0]->LastName = L"Olmos";
        std[0]->Gender = 2;

        std[1] = gcnew CStudent;
        std[1]->FirstName = L"Patricia";
        std[1]->LastName = L"Katts";
        std[1]->Gender = 1;

        std[2] = gcnew CStudent;
        std[2]->FirstName = L"Josiane";
        std[2]->LastName = L"Euler";
        std[2]->Gender = 1;

        std[3] = gcnew CStudent;
        std[3]->FirstName = L"Joan";
        std[3]->LastName = L"Jones";
        std[3]->Gender = 3;

        std[4] = gcnew CStudent;
        std[4]->FirstName = L"George";
        std[4]->LastName = L"Paulson";
        std[4]->Gender = 2;
    }
};

int main()
{
    CSchoolRegistration ^ pupils = gcnew CSchoolRegistration;

    for (int i = 0; i < 5; i++)
    {
        CStudent ^ pupil = pupils[i];

        Console::WriteLine(L"Student Information");
        Console::WriteLine(L"---------------------");
        Console::WriteLine(L"First Name: {0}", pupil->FirstName);
        Console::WriteLine(L"Last Name:  {0}", pupil->LastName);
        Console::WriteLine(L"Gender:     {0}\n",
                             (pupil->Gender == 1 ? "Female" :
                             (pupil->Gender == 2 ? "Male" : "Unknown")));
    }

    Console::WriteLine();
    return 0;
}

This would produce:

Student Information
---------------------
First Name: Alfredo
Last Name:  Olmos
Gender:     Male

Student Information
---------------------
First Name: Patricia
Last Name:  Katts
Gender:     Female

Student Information
---------------------
First Name: Josiane
Last Name:  Euler
Gender:     Female

Student Information
---------------------
First Name: Joan
Last Name:  Jones
Gender:     Unknown

Student Information
---------------------
First Name: George
Last Name:  Paulson
Gender:     Male

Press any key to continue . . .

1. To create an indexed property that takes an integer and returns an object, access the PropertyListing.h header file and change it as follows:
    

   #pragma once #include "RentalProperty.h" public ref class CPropertyListing { public: array<CRentalProperty ^> ^ props; property CRentalProperty ^ default[int] { CRentalProperty ^ get(int i) { return props[i]; } } property String ^ default[long] { String ^ get(long code) { . . . No Change } } public: CPropertyListing(void); };

2. Access the Exercise.cpp source file and change it as follows:
    

   using namespace System; #include "PropertyListing.h" int main() { CPropertyListing ^ properties = gcnew CPropertyListing; Console::WriteLine(L"Here is a list of our properties"); for (int i = 0; i < 6; i++) { CRentalProperty ^ prop = properties[i]; Console::WriteLine(L"Property Information"); Console::WriteLine(L"--------------------------------------"); Console::WriteLine(L"Property #: {0}", prop->PropertyCode); Console::WriteLine(L"Condition: {0}", prop->PropertyCondition); Console::WriteLine(L"Bedrooms: {0}", prop->Bedrooms); Console::WriteLine(L"Bathrooms: {0}", prop->Bathrooms); Console::WriteLine(L"Monthly Rent: {0}", prop->MonthlyRent.ToString("C")); Console::WriteLine(L"======================================"); } return 0; }

3. Press Ctrl + F5 to execute the application
4. Close the DOS window

The above implementation of the CSchoolRegistration class easily allowed us to locate an element of the array by specifying its integer-based index. As done for primitive types, an indexed property can take a parameter other than an integer. In some cases, you may use your class or a class created by someone else and need to access an element of the array without information other than its index. Consider the following program:

public ref class CStudent
{
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ students;

public:
    property CStudent ^ default[...]
    {
    }

    CSchoolRegistration()
    {
	students = gcnew array<CStudent ^>(50);
    }
};

Previously, we saw that you could create an indexed property that took a type other than an integer. For example, we saw that a string could be used as an index.

By now, we know that a basic indexed property produces (or all the indexed properties we have studied so far produce) only one value. If you have a class that has only one member variable, this would be enough. In reality, most of the time, a class has many member variables. In such a case, when you create an indexed property , you need to be able to refer to one exact element of the array. To make this possible, you must define a way to point to the particular element you want. One way you can do this is to use one member variable of the class as a reference. This is better if that member variable holds unique values among the other elements of the array. For our CStudent class, we could use the StudentID member variable (because we will make sure that each student has a unique ID). You can start the property as follows:

public ref class CSchoolRegistration
{
public:
    property CStudent ^ default[long]
    {
    }
};

When a user uses this property, he or she must provide a value that uniquely identifies an element of the array. You in turn, when you get this value, you can search for it in the array. If you find it and the array has a get accessor, you can then return the desired but appropriate value. Here is how this can be done:

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ students;

public:
    property CStudent ^ default[long]
    {
        CStudent ^ get(long id)
        {
            for (int i = 0; i < students->Length; i++)
            {
                if (students[i]->StudentID == id)
                    return students[i];
            }
            // Unknown student or the number was not found
            return nullptr;
        }
    }

    CSchoolRegistration()
    {
	students = gcnew array<CStudent ^>(50);
    }
};

After creating the indexed property, you can use it. Once again, you must follow the rules of a method that takes an argument and returns a value other than void. In this case, the indexed property must take a string and it must return a CStudent object. Here is an example:

using namespace System;

public enum Classification
{
    Female,
    Male,
    Unknown
};

public ref class CStudent
{
public:
    long StudentID;
    String ^ FirstName;
    String ^ LastName;
    Classification Gender;

    virtual String ^ ToString() override
    {
		String ^ str = String::Concat(L"Student ID: ", StudentID.ToString(),
                       L"\nFirst Name: ", FirstName,
                       L"\nLast Name:  ", LastName,
                       L"\nGender:     ", Gender);
        return str;
    }
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ students;

public:
	property CStudent ^ default[long]
    {
        CStudent ^ get(long id)
        {
            for (int i = 0; i < students->Length; i++)
            {
                if (students[i]->StudentID == id)
                    return students[i];
            }
            // Unknown student or the number was not found
            return nullptr;
        }
    }

    CSchoolRegistration()
    {
	students = gcnew array<CStudent ^>(50);

        students[0] = gcnew CStudent;
        students[0]->StudentID = 917294;
        students[0]->FirstName = L"Helene";
        students[0]->LastName = L"Mukoko";
	students[0]->Gender = Female;

        students[1] = gcnew CStudent;
        students[1]->StudentID = 283764;
        students[1]->FirstName = L"Patrice";
        students[1]->LastName = L"Katts";
        students[1]->Gender = Unknown;

        students[2] = gcnew CStudent;
        students[2]->StudentID = 192046;
        students[2]->FirstName = L"Armand";
        students[2]->LastName = L"Essono";
        students[2]->Gender = Male;

        students[3] = gcnew CStudent;
        students[3]->StudentID = 618268;
        students[3]->FirstName = L"Bertrand";
        students[3]->LastName = L"Yamaguchi";
        students[3]->Gender = Male;

        students[4] = gcnew CStudent;
        students[4]->StudentID = 820648;
        students[4]->FirstName = L"Hortense";
        students[4]->LastName = L"McNeal";
        students[4]->Gender = Female;
    }
};

int main()
{
    CSchoolRegistration ^ pupils = gcnew CSchoolRegistration;

    CStudent ^ pupil = pupils[820648];

    Console::WriteLine(L"Student Information");
    Console::WriteLine(L"---------------------");
    Console::WriteLine(L"First Name: {0}", pupil->FirstName);
    Console::WriteLine(L"Last Name:  {0}", pupil->LastName);
    Console::Write(L"Gender:     ");
	Console::WriteLine(pupil->Gender);

    pupil = pupils[192046];

    Console::WriteLine(L"Student Information");
    Console::WriteLine(L"---------------------");
    Console::WriteLine(L"First Name: {0}", pupil->FirstName);
    Console::WriteLine(L"Last Name:  {0}", pupil->LastName);
    Console::Write(L"Gender:     ");
    Console::WriteLine(pupil->Gender);

    return 0;
}

This would produce:

Student Information
---------------------
First Name: Hortense
Last Name:  McNeal
Gender:     Female

Student Information
---------------------
First Name: Armand
Last Name:  Essono
Gender:     Male

Press any key to continue . . .

As opposed to returning a class, an indexed property can use a class as its index. When creating such a property, the primary action you must take is to include a class and its name as a parameter to the default property. You can start such a class as follows:

public ref class CStudent
{
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ students;

public:
    property String ^ default[CStudent ^]
    {
    }

    CSchoolRegistration()
    {
        students = gcnew array<CStudent ^>(50);
    }
};

When implementing the class, you should proceed the same way we have done so far following the rules of a method that takes an argument and returns a value other than void. Here is an example:

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ students;

public:
    property String ^ default[CStudent ^]
    {
        String ^ get(CStudent ^ std)
        {
            for (int i = 0; i < students->Length; i++)
            {
		String ^ strGender =
			(students[i]->Gender == Female ? L"Female" :
			(students[i]->Gender == Male ? L"Male" : L"Unknown"));
                if (std->StudentID == students[i]->StudentID)
			return L"Student ID: " + students[i]->StudentID.ToString() +
 		 	       L"\nFirst Name: " + students[i]->FirstName +
                               L"\nLast Name:  " + students[i]->LastName +
                               L"\nGender:     " + strGender;
            }

            // Unknown student or the number was not found
            return L"Unknown";
        }
    }

    CSchoolRegistration()
    {
        students = gcnew array<CStudent ^>(50);
    }
};

After creating the property, you can use it. To do this, you must pass an object that is the type of the index. You can then use the returned value as you see fit. Here is an example:

using namespace System;

public enum Classification
{
    Female,
    Male,
    Unknown
};

public ref class CStudent
{
public:
	long StudentID;
    String ^ FirstName;
    String ^ LastName;
    Classification Gender;
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ students;

public:
    property String ^ default[CStudent ^]
    {
        String ^ get(CStudent ^ std)
        {
            for (int i = 0; i < students->Length; i++)
            {
		String ^ strGender =
			(students[i]->Gender == Female ? L"Female" :
				(students[i]->Gender == Male ? L"Male" : L"Unknown"));
                if (std->StudentID == students[i]->StudentID)
			return L"Student ID: " + students[i]->StudentID.ToString() +
	 	 	       L"\nFirst Name: " + students[i]->FirstName +
                               L"\nLast Name:  " + students[i]->LastName +
                               L"\nGender:     " + strGender;
            }

            // Unknown student or the number was not found
            return L"Unknown";
        }
    }

    CSchoolRegistration()
    {
        students = gcnew array<CStudent ^>(50);

        students[0] = gcnew CStudent();
        students[0]->StudentID = 917294;
        students[0]->FirstName = L"Helene";
        students[0]->LastName = L"Mukoko";
        students[0]->Gender = Female;

        students[1] = gcnew CStudent();
        students[1]->StudentID = 283764;
        students[1]->FirstName = L"Patrice";
        students[1]->LastName = L"Katts";
        students[1]->Gender = Unknown;

        students[2] = gcnew CStudent();
        students[2]->StudentID = 192046;
        students[2]->FirstName = L"Armand";
        students[2]->LastName = L"Essono";
        students[2]->Gender = Male;

        students[3] = gcnew CStudent();
        students[3]->StudentID = 618268;
        students[3]->FirstName = L"Bertrand";
        students[3]->LastName = L"Yamaguchi";
        students[3]->Gender = Male;

        students[4] = gcnew CStudent();
        students[4]->StudentID = 820648;
        students[4]->FirstName = L"Hortense";
        students[4]->LastName = L"McNeal";
        students[4]->Gender = Female;

        students[5] = gcnew CStudent();
        students[5]->StudentID  = 917394;
        students[5]->FirstName = L"Alfredo";
        students[5]->LastName = L"Olmos";
        students[5]->Gender = Unknown;

        students[6] = gcnew CStudent();
        students[6]->StudentID  = 163864;
        students[6]->FirstName = L"Josiane";
        students[6]->LastName = L"Euler";
        students[6]->Gender = Female;

        students[7] = gcnew CStudent();
        students[7]->StudentID  = 826384;
        students[7]->FirstName = L"Joan";
        students[7]->LastName = L"Jones";
        students[7]->Gender =  Female ;
    }
};

int main()
{
    CSchoolRegistration ^ pupils = gcnew CSchoolRegistration;

    CStudent ^ pupil = gcnew CStudent;
    pupil->StudentID = 820648;

    String ^ strStudent = pupils[pupil];

    Console::WriteLine(L"=====================");
    Console::WriteLine(L"Student Information");
    Console::WriteLine(L"---------------------");
    Console::WriteLine(strStudent);

    pupil->StudentID = 192046;
    strStudent = pupils[pupil];

    Console::WriteLine(L"=====================");
    Console::WriteLine(L"Student Information");
    Console::WriteLine(L"---------------------");
    Console::WriteLine(strStudent);

    Console::WriteLine(L"=====================\n");
    return 0;
}

This would produce:

=====================
Student Information
---------------------
Student ID: 820648
First Name: Hortense
Last Name:  McNeal
Gender:     Female
=====================
Student Information
---------------------
Student ID: 192046
First Name: Armand
Last Name:  Essono
Gender:     Male
=====================

Press any key to continue . . .

You can also directly pass an instance of the class in the square brackets of the object that holds the indexed property, as long as you specify the object. Here is an example:

public ref class CStudent
{
public:
    ... No Change
	
    CStudent()
    {
    }

    CStudent(long id)
    {
        this->StudentID = id;
    }
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ students;

public:
    property String ^ default[CStudent ^]
    {
        ... No Change
    }

    CSchoolRegistration()
    {
        students = gcnew array<CStudent ^>(50);

        ... No Change
    }
};

int main()
{
    CSchoolRegistration ^ pupils = gcnew CSchoolRegistration;

    String ^ strStudent = pupils[gcnew CStudent(826384)];
    Console::WriteLine(L"=====================");
    Console::WriteLine(L"Student Information");
    Console::WriteLine(L"---------------------");
    Console::WriteLine(strStudent);

    strStudent = pupils[gcnew CStudent(917394)];

    Console::WriteLine(L"=====================");
    Console::WriteLine(L"Student Information");
    Console::WriteLine(L"---------------------");
    Console::WriteLine(strStudent);

    Console::WriteLine(L"=====================\n");
    return 0;
}

This would produce:

=====================
Student Information
---------------------
Student ID: 826384
First Name: Joan
Last Name:  Jones
Gender:     Female
=====================
Student Information
---------------------
Student ID: 917394
First Name: Alfredo
Last Name:  Olmos
Gender:     Unknown
=====================

Press any key to continue . . .

As mentioned for indexed properties that return primitive types, you can overload an indexed property that produces a class. You do this following the same rules applied to method overloading and arrays:

• If two indexed properties take only one parameter, each must take a different type of parameter than the other. The parameter can be a primitive type or a class. Here are examples:
   

  using namespace System; public enum Classification { Female, Male, Unknown }; public ref class CMajor { public: String ^ Name; int CreditsRequired; }; public ref class CStudent { public: long StudentNumber; String ^ FullName; Classification Gender; virtual String ^ ToString() override { String ^ strGender = (Gender == Female ? L"Female" : (Gender == Male ? L"Male" : L"Unknown")); String ^ str = L"Student #: " + StudentNumber.ToString() + L"\nFull Name: " + FullName + L"\nGender: " + strGender; return str; } }; public ref class CStudentRegistration { private: array<CStudent ^> ^ std; public: CStudentRegistration() { std = gcnew array<CStudent ^>(5); std[0] = gcnew CStudent; std[0]->StudentNumber = 304850; std[0]->FullName = L"Helene Mukoko"; std[0]->Gender = Female; std[1] = gcnew CStudent; std[1]->StudentNumber = 926304; std[1]->FullName = L"Patrice Katts"; std[1]->Gender = Unknown; std[2] = gcnew CStudent; std[2]->StudentNumber = 330647; std[2]->FullName = L"Armand Essono"; std[2]->Gender = Male; std[3] = gcnew CStudent; std[3]->StudentNumber = 631846; std[3]->FullName = L"Bertrand Yamaguchi"; std[3]->Gender = Male; std[4] = gcnew CStudent; std[4]->StudentNumber = 209374; std[4]->FullName = L"Anselme Bongos"; std[4]->Gender = Male; } // This property takes a string and produces a Student object property CStudent ^ default[String ^] { CStudent ^ get(String ^ strFullName) { for (int i = 0; i < std->Length; i++) { if (std[i]->FullName == strFullName) return std[i]; } return nullptr; } } // This property takes a number and produces a Student object property CStudent ^ default[long] { CStudent ^ get(long nbr) { for (int i = 0; i < std->Length; i++) { if( nbr == std[i]->StudentNumber ) return std[i]; } return nullptr; } } // This property takes a major produces its definition property String ^ default[CMajor ^] { String ^ get(CMajor ^ maj) { return "Major: " + maj->Name + " - " + maj->CreditsRequired + " Credits Required"; } } }; int main() { CStudentRegistration ^ pupils = gcnew CStudentRegistration(); CMajor ^ m1 = gcnew CMajor; m1->Name = L"Computer Sciences"; m1->CreditsRequired = 120; CMajor ^ m2 = gcnew CMajor; m2->Name = L"Informtation Technology"; m2->CreditsRequired = 120; Console::WriteLine(L"=-= Student Identification =-="); Console::WriteLine(pupils["Helene Mukoko"]); Console::WriteLine(pupils[m1]); Console::WriteLine(L"--------------------------------------------------"); Console::WriteLine(L"=-= Student Identification =-="); Console::WriteLine(pupils[330647]); Console::WriteLine(pupils[m2]); Console::WriteLine(L"--------------------------------------------------"); Console::WriteLine(); return 0; }

  This would produce:

  =-= Student Identification =-= Student #: 304850 Full Name: Helene Mukoko Gender: Female Major: Computer Sciences - 120 Credits Required -------------------------------------------------- =-= Student Identification =-= Student #: 330647 Full Name: Armand Essono Gender: Male Major: Information Technology - 120 Credits Required -------------------------------------------------- Press any key to continue . . .

• If one property takes only one parameter, the other(s) can take more than one parameter. An indexed property can take different parameters of primitive types as seen in the previous lesson. A property can also take two or more classes as parameters. An indexed property can also take a mix of primitive and class types as parameters.
  Here are examples:
   

  using namespace System; public enum Classification { Female, Male, Unknown }; public ref class CStudent { public: long StudentID; String ^ FirstName; String ^ LastName; Classification Gender; CStudent() { } CStudent(long id) { this->StudentID = id; } virtual String ^ ToString() override { String ^ strGender = (Gender == Female ? L"Female" : (Gender == Male ? L"Male" : L"Unknown")); return "Student ID: " + StudentID + "\nFirst Name: " + FirstName + "\nLast Name: " + LastName + "\nGender: " + strGender; } }; public enum CourseDelivery { FaceToFace, Online, Both // Student Choose }; public ref class CCourse { public: String ^ ShortName; String ^ LongName; String ^ Description; public: int Credits; CourseDelivery DeliveryMode; CCourse() { } CCourse(String ^ name) { ShortName = name; } virtual String ^ ToString() override { String ^ strDeliveryMode = (DeliveryMode == FaceToFace ? L"Face-to-Face" : (DeliveryMode == Online ? L"Online" : L"Both")); return "Course: " + ShortName + "\nFull Name: " + LongName + "\nCredits: " + Credits + "\nDescription: " + Description + "\nDelivery: " + strDeliveryMode; } }; public ref class CSchoolRegistration { array<CStudent ^> ^ students; array<CCourse ^> ^ classes; // This indexed property takes a student id and // returns the student information public: property CStudent ^ default[long] { CStudent ^ get(long id) { for (int i = 0; i < students->Length; i++) { if (id == students[i]->StudentID) return students[i]; } // Unknown student or the number was not found return nullptr; } } // This indexed property takes a course short name and // it produces a summary of the course information property CCourse ^ default[String ^] { CCourse ^ get(String ^ name) { for (int i = 0; i < classes->Length; i++) { if (name == classes[i]->ShortName) return classes[i]; } // Unknown course return nullptr; } } property String ^ default[CCourse ^, CStudent ^] { String ^ get(CCourse ^ ToAttend, CStudent ^ registrant) { // First check that the class exists for (int i = 0; i < classes->Length; i++) { if (ToAttend->ShortName == classes[i]->ShortName) { // If the class exists, then check if the student exists for (int j = 0; j < students->Length; j++) { if (registrant->StudentID == students[j]->StudentID) { String ^ strDeliveryMode = (classes[i]->DeliveryMode == FaceToFace ? L"Face-to-Face" : (classes[i]->DeliveryMode == Online ? L"Online" : L"Both")); return L"Student Identification --\n Student ID: " + students[j]->StudentID + L"\n Full Name: " + students[j]->LastName + L", " + students[j]->FirstName + L"\nClass to Attend --\n Course: " + classes[i]->ShortName + " - " + classes[i]->LongName + " (" + classes[i]->Credits + ")" + L"\n Delivery: " + strDeliveryMode; } } } } return L"Invalid Registration - You may have to start over"; } } // This property takes information used to register // a student to a course // It also specifies whether the student is willing // to get in the waiting list in case another students drops out property String ^ default[CStudent ^, CCourse ^, bool] { String ^ get(CStudent ^ stud, CCourse ^ Class, bool WaitingList) { // Check that the student information is valie for (int j = 0; j < students->Length; j++) { if (stud->StudentID == students[j]->StudentID) { // Now that the student information has been found, // check if the course information is correct for (int i = 0; i < classes->Length; i++) { if (Class->ShortName == classes[i]->ShortName) { String ^ strDeliveryMode = (classes[i]->DeliveryMode == FaceToFace ? L"Face-to-Face" : (classes[i]->DeliveryMode == Online ? L"Online" : L"Both")); // If the class exists, then check if the student exists return L"Student Identification --\n Student ID: " + students[j]->StudentID + L"\n Full Name: " + students[j]->LastName + L", " + students[j]->FirstName + L"\nClass to Attend --\n Course: " + classes[i]->ShortName + " - " + classes[i]->LongName + " (" + classes[i]->Credits + ")" + L"\n Delivery: " + strDeliveryMode + L"\nStudent is willing to get on the waiting list: " + + WaitingList; } } } } return L"Invalid Registration - You may have to start over"; } } CSchoolRegistration() { students = gcnew array<CStudent ^>(50); classes = gcnew array<CCourse ^>(3); students[0] = gcnew CStudent; students[0]->StudentID = 917294; students[0]->FirstName = L"Helene"; students[0]->LastName = L"Mukoko"; students[0]->Gender = Female; students[1] = gcnew CStudent; students[1]->StudentID = 283764; students[1]->FirstName = L"Patrice"; students[1]->LastName = L"Katts"; students[1]->Gender = Unknown; students[2] = gcnew CStudent; students[2]->StudentID = 192046; students[2]->FirstName = L"Armand"; students[2]->LastName = L"Essono"; students[2]->Gender = Male; students[3] = gcnew CStudent; students[3]->StudentID = 618268; students[3]->FirstName = L"Bertrand"; students[3]->LastName = L"Yamaguchi"; students[3]->Gender = Male; students[4] = gcnew CStudent; students[4]->StudentID = 820648; students[4]->FirstName = L"Hortense"; students[4]->LastName = L"McNeal"; students[4]->Gender = Female; classes[0] = gcnew CCourse; classes[0]->ShortName = L"PHIL140"; classes[0]->LongName = L"Philosophy - Contemporary Moral Issues"; classes[0]->Credits = 3; classes[0]->Description = L"An exploration of how philosophical analysis can be " L"\n\t\ta foundation for thinking clearly about moral issues. " L"\n\t\tProblems analyzed include such widely debated issues " L"\n\t\tas abortion, euthanasia, the death penalty, " L"\n\t\thomosexuality, pornography, reverse discrimination, " L"\n\t\tbusiness ethics, sexual equality, and economic equity."; classes[1] = gcnew CCourse; classes[1]->ShortName = L"MATH140"; classes[1]->LongName = L"Calculus I"; classes[1]->Credits = 4; classes[1]->Description = L"An introduction to calculus. Topics include functions, " L"\n\t\tthe sketching of graphs of functions, limits, continuity, " L"\n\t\tderivatives and applications of the derivative, definite " L"\n\t\tand indefinite integrals, and calculation of area."; classes[2] = gcnew CCourse; classes[2]->ShortName = L"ASTR100"; classes[2]->LongName = L"Introduction to Astronomy"; classes[2]->Credits = 3; classes[2]->Description = L"A discussion of the major areas of astronomy. Topics " L"\n\t\tinclude the solar system, stars and stellar evolution, " L"\n\t\tand galaxies. Current topics in astronomy are also " L"\n\t\tdiscussed."; } }; int main() { CSchoolRegistration ^ pupils = gcnew CSchoolRegistration; CStudent ^ std = gcnew CStudent(917294); CCourse ^ crs = gcnew CCourse("MATH140"); Console::WriteLine(L"================================================"); Console::WriteLine(L"Student Registration"); Console::WriteLine(L"------------------------------------------"); Console::WriteLine(pupils[crs, std]); std = gcnew CStudent(820648); crs = gcnew CCourse("PHIL140"); Console::WriteLine(L"================================================"); Console::WriteLine(L"Student Registration"); Console::WriteLine(L"------------------------------------------"); Console::WriteLine(pupils[std, crs, true]); Console::WriteLine(L"================================================\n"); return 0; }

  This would produce:

  ================================================ Student Registration ------------------------------------------ Student Identification -- Student ID: 917294 Full Name: Mukoko, Helene Class to Attend -- Course: MATH140 - Calculus I (4) Delivery: Face-to-Face ================================================ Student Registration ------------------------------------------ Student Identification -- Student ID: 820648 Full Name: McNeal, Hortense Class to Attend -- Course: PHIL140 - Philosophy - Contemporary Moral Issues (3) Delivery: Face-to-Face Student is willing to get on the waiting list: True ================================================ Press any key to continue . . .

1. To overload the indexed property, access the PropertyListing.h header file and change it as follows:
    

   #pragma once #include "RentalProperty.h" public ref class CPropertyListing { public: array<CRentalProperty ^> ^ props; property CRentalProperty ^ default[int] { CRentalProperty ^ get(int i) { if ((i >= 0) && (i < 40)) return props[i]; else return nullptr; } } property CRentalProperty ^ default[long] { CRentalProperty ^ get(long code) { for (int i = 0; i < props->Length; i++) if (code == props[i]->PropertyCode) return props[i]; return nullptr; } } public: CPropertyListing(void); };

2. Access the Exercise.cpp source file and change it as follows:
    

   using namespace System; #include "PropertyListing.h" int main() { CPropertyListing ^ properties = gcnew CPropertyListing(); long lngCode; Console::WriteLine(L"Here is a list of our properties by code"); for(int i = 0; i < 6; i++) Console::WriteLine(L"Property Code: {0}", properties->props[i]->PropertyCode); try { Console::Write("Enter Property Code: "); lngCode = long::Parse(Console::ReadLine()); Console::WriteLine(L"======================================"); Console::WriteLine(L"Property Information"); Console::WriteLine(L"--------------------------------------"); Console::WriteLine(properties[lngCode]); Console::WriteLine(L"======================================"); } catch(FormatException ^) { Console::WriteLine(L"=- Invalid Property Code -="); } return 0; }

3. Press Ctrl + F5 to execute the application 
4. Close the DOS window

As done for a primitive type, you can allow the clients of your indexed property to assign values to the array's elements. Once again, when defining the property, you should include a set accessor to it. You must pass two parameters to the set accessor. The first parameter is used to identify the index of the array element that will receive the value. The second parameter holds the value that will be assigned to the element of the indexed property. Here is an example:

public ref class CSchoolRegistration
{
    array<CStudent ^> ^  std;

public:
    property CStudent ^ default[int]
    {
        CStudent ^ get(int i) { return std[i]; }
        void set(int i, CStudent ^ value) { std[i] = value; }
    }

    CSchoolRegistration()
    {
	std = gcnew array<CStudent ^>(5);
    }
};

After doing this, you can create an element of the array by applying the square brackets to the instance of the class and assigning the desired value to it. The problem with the class is that, since it may have many member variables (or properties), to completely define each element, you must provide a value to the member variables of the class itself. Here is an example:

using namespace System;

public ref class CStudent
{
public:
    long StudentID;
    String ^ FirstName;
    String ^ LastName;
    String ^ Gender;

    virtual String ^ ToString() override
    {
        String ^ str = L"Student ID: " + StudentID +
                       L"\nFirst Name: " + FirstName +
                       L"\nLast Name:  " + LastName +
                       L"\nGender:     " + Gender;
        return str;
    }
};

public ref class CSchoolRegistration
{
    array<CStudent ^> ^ std;

public:
    property CStudent ^ default[int]
    {
        CStudent ^ get(int i) { return std[i]; }
        void set(int i, CStudent ^ value)
	{
	    std[i] = value;
	}
    }

    CSchoolRegistration()
    {
	std = gcnew array<CStudent ^>(5);
    }
};

int main()
{
    CSchoolRegistration ^ registration = gcnew CSchoolRegistration;

    CStudent ^ stud = gcnew CStudent;
    stud->StudentID = 604057;
    stud->FirstName = L"Gertrude";
    stud->LastName  = L"Monayong";
    stud->Gender    = L"Female";
        
    registration[2] = stud;

    Console::WriteLine(L"Student Information");
    Console::WriteLine(L"---------------------");
    Console::WriteLine(L"First Name: {0}", registration[2]->FirstName);
    Console::WriteLine(L"Last Name:  {0}", registration[2]->LastName);
    Console::WriteLine(L"Gender:     {0}\n", registration[2]->Gender);
         
    return 0;
}

This would produce:

Student Information
---------------------
First Name: Gertrude
Last Name:  Monayong
Gender:     Female

Press any key to continue . . .

1. To combine some of the topics we have studied so far, we will create a serializable list of rental properties in a file based database application.
   To create a new application, on the main menu, click File -> New -> Project...
2. In the Templates list, click CLR Empty Project.
   Set the Name to SolasPropertRental1 and click OK
3. To create a new class, in the Solution Explorer, right-click SolasPropertyRental1 -> Add -> Class...
4. In the Templates list, click C++ Class and click Add
5. Set the Name to CRentalProperty and click Finish
6. Implement the header file as follows:
    

   #pragma once using namespace System; [Serializable] public ref class CRentalProperty { private: // These are the characteristics of a property long propCode; String ^ type; String ^ cond; short beds; double baths; double val; public: property long PropertyCode { long get() { return propCode; } void set(long value) { propCode = value; } } property String ^ PropertyType { String ^ get() { return type; } void set(String ^ value) { type = value; } } property String ^ PropertyCondition { String ^ get() { return cond; } void set(String ^ value) { cond = value; } } property short Bedrooms { short get() { return beds; } void set(short value) { beds = value; } } property double Bathrooms { double get() { return (baths <= 0) ? 0.00 : baths; } void set(double value) { baths = value; } } property double MonthlyRent { double get() { return (val <= 0) ? 0.00 : val; } void set(double value) { val = value; } } // This flag is used to specify whether a property // still holds the default values or it has // previously been updated int CreationFlag; public: // This constructor is used to create // default values for a property CRentalProperty(void); virtual String ^ ToString() override; };

7. Access the RentalProperty.cpp source file and change it as follows:
    

   #include "RentalProperty.h" CRentalProperty::CRentalProperty(void) { Random ^ rnd = gcnew Random(); propCode = rnd->Next(100000, 999999); type = L"Unknown"; cond = L"Unknown"; beds = 0; baths = 0.0; val = 0.00; CreationFlag = 0; } // This method is used to create a string that // the characteristics of a property String ^ CRentalProperty::ToString() { return L"Property #: " + PropertyCode + L"\nType: " + PropertyType + L"\nCondition: " + PropertyCondition + L"\nBedrooms: " + Bedrooms + L"\nBathrooms: " + Bathrooms + L"\nMonthly Rent: " + MonthlyRent.ToString("C"); }

8. To create a new class, in the Class View, right-click SolasPropertyRental1 -> Add -> Class...
9. In the Templates list, click C++ Class and click Add
10. Set the Name to CPropertyListing and click Finish
11. Change the header file as follows:
     

    #pragma once #include "RentalProperty.h" using namespace System::IO; using namespace System::Runtime::Serialization; using namespace System::Runtime::Serialization::Formatters::Binary; public ref class CPropertyListing { public: array<CRentalProperty ^> ^ props; property CRentalProperty ^ default[int] { CRentalProperty ^ get(int i) { if( (i >= 0) && (i < 100) ) return props[i]; else return nullptr; } void set(int i, CRentalProperty ^ value) { props[i] = value; } } public: CPropertyListing(void); };

12. In the Class View, right-click CPropertyListing -> Add -> Function...
13. Set the Return Type to void
    Set the Function Name to SaveProperties
    Click Finish and implement the method as follows:
     

    void CPropertyListing::SaveProperties() { String ^ strFilename = L"Properties.prp"; FileStream ^ fstProperties = gcnew FileStream(strFilename, FileMode::Create); BinaryFormatter ^ bfmProperties = gcnew BinaryFormatter; try { bfmProperties->Serialize(fstProperties, this->props); } catch(ArgumentNullException ^) { Console::WriteLine(L"The properties listing is not available"); } catch(SerializationException ^) { Console::WriteLine(L"The listing could not be saved"); } finally { fstProperties->Close(); } }

14. In the Class View, right-click CPropertyListing -> Add -> Function...
15. Set the Return Type to void
    Set the Function Name to CreateDefaultListing
    Click Finish and implement the method as follows:
     

    void CPropertyListing::CreateDefaultListing(void) { Random ^ rndNumber = gcnew Random; for(int i = 0; i < 100; i++) { CRentalProperty ^ rental = gcnew CRentalProperty; rental->PropertyCode = rndNumber->Next(100000, 999999); rental->PropertyType = L"Unknown"; rental->PropertyCondition = L"Unknown"; rental->Bedrooms = 0; rental->Bathrooms = 0; rental->MonthlyRent = 0.00; rental->CreationFlag = 0; props[i] = rental; } SaveProperties(); }

16. In the Class View, right-click CPropertyListing -> Add -> Function...
17. Set the Return Type to void
    Set the Function Name to OpenProperties
    Click Finish and implement the method as follows:
     

    void CPropertyListing::OpenProperties(void) { String ^ strFilename = L"Properties.prp"; FileStream ^ fstProperties = nullptr; BinaryFormatter ^ bfmProperties = nullptr; // If the list of properties had already been created // then open it if( File::Exists(strFilename) ) { try { fstProperties = gcnew FileStream(strFilename, FileMode::Open); bfmProperties = gcnew BinaryFormatter; this->props = dynamic_cast<array<CRentalProperty ^>^>( bfmProperties->Deserialize(fstProperties)); } catch(ArgumentNullException ^) { Console::WriteLine( L"The properties listing is not available"); } catch(SerializationException ^) { Console::WriteLine(L"The listing could not be opened"); } finally { fstProperties->Close(); } } else return; }

18. In the Class View, right-click CPropertyListing -> Add -> Function...
19. Set the Return Type to void
    Set the Function Name to ShowProperties
    Click Finish and implement the method as follows:
     

    void CPropertyListing::ShowProperties(void) { OpenProperties(); Console::WriteLine(L"Here is a list of our properties"); for(int i = 0; i < 26; i++) { Console::WriteLine(L"{0}.----------------------------------", i + 1); Console::WriteLine(props[i]); } Console::WriteLine(L"======================================"); }

20. In the Class View, right-click CPropertyListing -> Add -> Function...
21. Set the Return Type to void
    Set the Function Name to CreateProperty
    Click Finish and implement the method as follows:
     

    void CPropertyListing::CreateProperty(void) { CRentalProperty ^ prop = gcnew CRentalProperty; for(int i = 0; i < 100; i++) { if( props[i]->CreationFlag == 0 ) { try { Console::WriteLine(L"New Property Entry"); Console::WriteLine(L"Property Types"); Console::WriteLine(L"1 - Single Family"); Console::WriteLine(L"2 - Townhouse"); Console::WriteLine(L"3 - Apartment"); Console::Write(L"Enter your choice(1, 2, or 3): "); int type = int::Parse(Console::ReadLine()); if( type == 1 ) props[i]->PropertyType = L"Single Family"; else if( type == 2 ) props[i]->PropertyType = L"Townhouse"; else if( type == 3 ) props[i]->PropertyType = L"Apartment"; else props[i]->PropertyType = L"Unknown"; } catch(FormatException ^) { Console::WriteLine(L"Invalid Choice"); } try { Console::WriteLine(L"Property Conditions"); Console::WriteLine(L"1 - Excellent"); Console::WriteLine(L"2 - Good"); Console::WriteLine(L"3 - Bad Shape"); Console::Write(L"Enter your choice(1, 2, or 3): "); int cond = int::Parse(Console::ReadLine()); if( cond == 1 ) props[i]->PropertyCondition = L"Excellent"; else if( cond == 2 ) props[i]->PropertyCondition = L"Good"; else if( cond == 3 ) props[i]->PropertyCondition = L"Bad Shape"; else props[i]->PropertyCondition = L"Unknown"; } catch(FormatException ^) { Console::WriteLine(L"Invalid Selection"); } try { Console::Write(L"How many bedrooms? "); props[i]->Bedrooms = short::Parse(Console::ReadLine()); } catch(FormatException ^) { Console::WriteLine("Invalid Value"); } try { Console::Write(L"How many bathrooms? "); props[i]->Bathrooms = double::Parse(Console::ReadLine()); } catch(FormatException ^) { Console::WriteLine("Invalid Value"); } try { Console::Write(L"Monthly Rent: "); props[i]->MonthlyRent = double::Parse(Console::ReadLine()); } catch(FormatException ^) { Console::WriteLine("Unrecognizable Value"); } props[i]->CreationFlag = 1; SaveProperties(); return; } } Console::WriteLine(L"You cannot create a new property." L"You can only modify or replace an existing one."); }

22. In the Class View, right-click CPropertyListing -> Add -> Function...
23. Set the Return Type to void
    Set the Function Name to ShowProperty
    Click Finish and implement the method as follows:
     

    void CPropertyListing::ShowProperty(void) { try { OpenProperties(); Console::WriteLine( L"Here is a list of our properties by code"); for (int i = 0; i < 26; i++) Console::WriteLine(L"Property Code: {0}", props[i]->PropertyCode); Console::Write(L"Enter Property Code: "); long code = long::Parse(Console::ReadLine()); for(int i = 0; i < 100; i++) { if( props[i]->PropertyCode == code ) { Console::WriteLine( L"======================================"); Console::WriteLine(L"Property Information"); Console::WriteLine( L"--------------------------------------"); Console::WriteLine(props[i]); Console::WriteLine( L"======================================"); } } } catch(FormatException ^) { Console::WriteLine(L"=- Invalid Property Code -="); } }

24. Scroll up the PropertyListing.cpp source file and change the constructor as follows:
     

    #include "PropertyListing.h" CPropertyListing::CPropertyListing(void) { props = gcnew array<CRentalProperty ^>(100); // Check if the default list of properties has never been created. // If there is no default list of properties, // Then create it and save the file if( !File::Exists(L"Properties.prp") ) { CreateDefaultListing(); } // Since we have a file that holds the list of properties // open it and store the properties in our array OpenProperties(); }

25. To create a new source file, on the main menu, click Project -> Add New Item...
26. In the Templates list, click C++ File (.cpp)
27. Set the Name to Exercise and press Enter
28. Implement the file as follows:
     

    using namespace System; #include "PropertyListing.h" int main() { CPropertyListing ^ properties = gcnew CPropertyListing(); int choice = 0; do { try { Console::WriteLine(L"=================================="); Console::WriteLine(L"What do you want to do?"); Console::WriteLine(L"1. Create a new property"); Console::WriteLine(L"2. See one particular property"); Console::WriteLine(L"3. Show the properties"); Console::WriteLine(L"0. Quit"); Console::Write(L"Your Choice? "); choice = int::Parse(Console::ReadLine()); Console::WriteLine(L"----------------------------------"); if( choice == 1 ) properties->CreateProperty(); else if( choice == 2 ) properties->ShowProperty(); else if( choice == 3 ) properties->ShowProperties(); } catch(FormatException ^) { Console::WriteLine(L"Invalide Choice"); } }while( (choice > 0) && (choice < 4) ); return 0; }

29. Execute the application to test it