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Arrays and Classes: An Array of Objects

 

Introduction

As done for primitive values, you can create an array of a class type, using the [] operator. Here is an example:

class CSquare
{
public:
    double Side;

    CSquare() : Side(0.00) {}
    CSquare(double side) : Side(side) { }
    ~CSquare() { }

    double getSide() const { return Side; }
    void setSide(const double s)
    {
	if( s <= 0 )
	    Side = 0.00;
	else
	    Side = s;
    }

    double Perimeter() { return Side * 4; }
    double Area() { return Side * Side; }
};

int main()
{
    CSquare sqr[4];

    return 0;
}

To use the array, you can access the members of each element using the period operator on the right side of the [] operator. Here is an example:

using namespace System;

class CSquare
{
public:
    double Side;

    CSquare() : Side(0.00) {}
    CSquare(double side) : Side(side) { }
    ~CSquare() { }

    double getSide() { return Side; }
    void setSide(double s)
    {
	if( s <= 0 )
		Side = 0.00;
	else
		Side = s;
    }

    double Perimeter() { return Side * 4; }
    double Area() { return Side * Side; }
};

int main()
{
    CSquare sqr[4];

    sqr[0].Side = 24.55;
    sqr[1].Side = 15.08;
    sqr[2].Side = 8.212;
    sqr[3].Side = 202.24;

    Console::WriteLine(L"Squares Characteristics");
    Console::WriteLine(L"Square     1");
    Console::WriteLine(L"Side:      {0}", sqr[0].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[0].Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[0].Area());

    Console::WriteLine(L"Square     2");
    Console::WriteLine(L"Side:      {0}", sqr[1].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[1].Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[1].Area());

    Console::WriteLine(L"Square     3");
    Console::WriteLine(L"Side:      {0}", sqr[2].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[2].Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[2].Area());
	
    Console::WriteLine(L"Square     4");
    Console::WriteLine(L"Side:      {0}", sqr[3].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[3].Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[3].Area());

    return 0;
}

This would produce:

Squares Characteristics
Square     1
Side:      24.55
Perimeter: 98.2
Area:      602.702
Square     2
Side:      15.08
Perimeter: 60.32
Area:      227.406
Square     3
Side:      8.212
Perimeter: 32.848
Area:      67.4369
Square     4
Side:      202.24
Perimeter: 808.96
Area:      40901
Press any key to continue . . .

An Array of Pointers

You can also create the array as a collection of pointers. To declare the array, use the asterisk operator after the name of the class and indicate that the variable is an array by including a dimension in the square brackets on the right side of the variable. Here is an example:

CSquare *sqr[4];

To access each element of the array, get to its index and initialize it using the new operator as you would a pointer. Here is an example:

sqr[0] = new CSquare;

To access a member of an element of the array, use the -> operator applied on its index. Here are examples:

using namespace System;

class CSquare
{
public:
    double Side;

    CSquare() : Side(0.00) {}
    CSquare(double side) : Side(side) { }
    ~CSquare() { }

    double getSide() { return Side; }
    void setSide(double s)
    {
	if( s <= 0 )
		Side = 0.00;
	else
		Side = s;
    }

    double Perimeter() { return Side * 4; }
    double Area() { return Side * Side; }
};

int main()
{
    CSquare *sqr[4];

    sqr[0] = new CSquare;
    sqr[0]->setSide(24.55);
    sqr[1] = new CSquare;
    sqr[1]->setSide(15.08);
    sqr[2] = new CSquare;
    sqr[2]->setSide(8.212);
    sqr[3] = new CSquare;
    sqr[3]->setSide(202.24);

    Console::WriteLine(L"Squares Characteristics");
    Console::WriteLine(L"Square     1");
    Console::WriteLine(L"Side:      {0}", sqr[0]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[0]->Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[0]->Area());

    Console::WriteLine(L"Square     2");
    Console::WriteLine(L"Side:      {0}", sqr[1]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[1]->Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[1]->Area());

    Console::WriteLine(L"Square     3");
    Console::WriteLine(L"Side:      {0}", sqr[2]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[2]->Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[2]->Area());
	
    Console::WriteLine(L"Square     4");
    Console::WriteLine(L"Side:      {0}", sqr[3]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[3]->Perimeter());
    Console::WriteLine(L"Area:      {0}", sqr[3]->Area());

    return 0;
}

An Array of Handles

Like a primitive class, a class can be used to create an array of objects. You can create the array as a handle. If the class is a value type, you can follow the same rules as a primitive type to declare the array. Here is an example:

array<CSquare> ^ sqr = gcnew array<CSquare>(4);

To access each element of the array, use the period operator, exactly as we did for the array of simple objects. Here are examples:

using namespace System;

public value class CSquare
{
private:
    double sd;

public:
    CSquare(double side) : sd(side) { }

    property double Side
    {
	double get() { return sd; }
	void set(double s)
	{
	    if( s <= 0 )
		sd = 0.00;
	    else
		sd = s;
	}
    }

    property double Perimeter { double get() { return sd * 4; } }
    property double Area { double get() { return sd * sd; } }
};

int main()
{
    array<CSquare> ^ sqr = gcnew array<CSquare>(4);

    sqr[0].Side = 24.55;
    sqr[1].Side = 15.08;
    sqr[2].Side = 8.212;
    sqr[3].Side = 202.24;

    Console::WriteLine(L"Squares Characteristics");
    Console::WriteLine(L"Square 1----------");
    Console::WriteLine(L"Side:      {0}", sqr[0].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[0].Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[0].Area);

    Console::WriteLine(L"Square 2----------");
    Console::WriteLine(L"Side:      {0}", sqr[1].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[1].Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[1].Area);

    Console::WriteLine(L"Square 3----------");
    Console::WriteLine(L"Side:      {0}", sqr[2].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[2].Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[2].Area);
	
    Console::WriteLine(L"Square 4----------");
    Console::WriteLine(L"Side:      {0}", sqr[3].Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[3].Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[3].Area);

    return 0;
}

This would produce:

Squares Characteristics
Square 1----------
Side:      24.55
Perimeter: 98.2
Area:      602.7025

Square 2----------
Side:      15.08
Perimeter: 60.32
Area:      227.4064

Square 3----------
Side:      8.212
Perimeter: 32.848
Area:      67.436944

Square 4----------
Side:      202.24
Perimeter: 808.96
Area:      40901.0176

Press any key to continue . . .

Practical LearningPractical Learning: Creating an Array of Objects

  1. On the main menu, click File -> New -> Project...
  2. On the left side, make sure that Visual C++ is selected. In the Templates list, click CLR Empty Project
  3. In the Name box, replace the string with RealEstate14 and click OK
  4. To create a source file, on the main menu, click Project -> Add New Item...
  5. In the Templates list, click Source File (.cpp)
  6. In the New box, type Exercise and click Add
  7. In the empty file, type:
     
    using namespace System;
    	
    public value class CHouse
    {
    public:
        __wchar_t TypeOfHome;
        int NumberOfBedrooms;
        Byte Stories;
        double NumberOfBathrooms;
        int YearBuilt;
        bool HasGarage;
        double Value;
    };
    
    int main()
    {
        array<CHouse> ^ home = gcnew array<CHouse>(4);
    
        home[0].TypeOfHome = L'S';
        home[0].NumberOfBedrooms = 5;
        home[0].Stories = 3;
        home[0].NumberOfBathrooms = 3.5;
        home[0].YearBuilt = 1955;
        home[0].HasGarage = true;
        home[0].Value = 550500;
    
        home[1].TypeOfHome = L'C';
        home[1].NumberOfBedrooms = 2;
        home[1].Stories = 1;
        home[1].NumberOfBathrooms = 1.0;
        home[1].YearBuilt = 1988;
        home[1].HasGarage = true;
        home[1].Value = 115000;
    
        home[2].TypeOfHome = L'S';
        home[2].NumberOfBedrooms = 3;
        home[2].Stories = 3;
        home[2].NumberOfBathrooms = 2.5;
        home[2].YearBuilt = 1998;
        home[2].HasGarage = false;
        home[2].Value = 425000;
    
        home[3].TypeOfHome = L'T';
        home[3].NumberOfBedrooms = 3;
        home[3].Stories = 2;
        home[3].NumberOfBathrooms = 1.5;
        home[3].YearBuilt = 1962;
        home[3].HasGarage = false;
        home[3].Value = 350000;
    
        Console::WriteLine(L"=======================================");
        Console::WriteLine(L"Altair Realtors");
        Console::WriteLine(L"---------------------------------------");
        Console::WriteLine(L"Real Estate Properties Inventory");
        Console::WriteLine(L"---------------------------------------");
        Console::WriteLine(
    	L"Type  Bedrooms  Stories  Bathrooms  Year  Garage  Value");
        Console::WriteLine(
    	L"=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=");
        for each(CHouse prop in home)
        {
            Console::WriteLine(L"{0,2}{1,8}{2,10}{3,10}{4,10}{5,7}{6,8}",
    			   prop.TypeOfHome, prop.NumberOfBedrooms,
    			   prop.Stories, prop.NumberOfBathrooms,
    			   prop.YearBuilt, prop.HasGarage, prop.Value);
    	Console::WriteLine(
    	    L"---------------------------------------------------------");
        }
    
        Console::WriteLine(
    		L"=========================================================");
        return 0;
    }
  8. To execute the application, on the main menu, click Debug -> Start Without Debugging
     
    =======================================
    Altair Realtors
    ---------------------------------------
    Real Estate Properties Inventory
    ---------------------------------------
    Type  Bedrooms  Stories  Bathrooms  Year  Garage  Value
    =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
     S       5         3       3.5      1955   True  550500
    ---------------------------------------------------------
     C       2         1         1      1988   True  115000
    ---------------------------------------------------------
     S       3         3       2.5      1998  False  425000
    ---------------------------------------------------------
     T       3         2       1.5      1962  False  350000
    ---------------------------------------------------------
    =========================================================
    Press any key to continue . . .
  9. Close the DOS window

An Array Element as a Pointer

When creating the array, you can treat each element as a pointer. To specify this, inside of the <> operator, type * on the right side of the class's name. Here is an example:

array<CSquare *> ^ sqr = gcnew array<CSquare *>(4);

Before using an element of the array, you must allocate memory for it. This is done using the new operator. Here is an example:

array<CSquare *> ^ sqr = gcnew array<CSquare *>(4);

sqr[0] = new CSquare;

To access a member variable or a method of an element, you can use the -> operator. Here are examples:

using namespace System;

public value class CSquare
{
private:
    double sd;

public:
    CSquare(double side) : sd(side) { }

    property double Side
    {
	double get() { return sd; }
	void set(double s)
	{
	    if( s <= 0 )
		sd = 0.00;
	    else
		sd = s;
	}
    }

    property double Perimeter { double get() { return sd * 4; } }
    property double Area { double get() { return sd * sd; } }
};

int main()
{
    array<CSquare *> ^ sqr = gcnew array<CSquare *>(4);

    sqr[0] = new CSquare;
    sqr[0]->Side = 24.55;
    sqr[1] = new CSquare;
    sqr[1]->Side = 15.08;
    sqr[2] = new CSquare;
    sqr[2]->Side = 8.212;
    sqr[3] = new CSquare;
    sqr[3]->Side = 202.24;

    Console::WriteLine(L"Squares Characteristics");
    Console::WriteLine(L"Square 1----------");
    Console::WriteLine(L"Side:      {0}", sqr[0]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[0]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[0]->Area);

    Console::WriteLine(L"Square 2----------");
    Console::WriteLine(L"Side:      {0}", sqr[1]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[1]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[1]->Area);

    Console::WriteLine(L"Square 3----------");
    Console::WriteLine(L"Side:      {0}", sqr[2]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[2]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[2]->Area);
	
    Console::WriteLine(L"Square 4----------");
    Console::WriteLine(L"Side:      {0}", sqr[3]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[3]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[3]->Area);

    return 0;
}

An Array Element as a Handle

If the class is a ref type, then when using the array, each element must be treated as a handle. When declaring the array, you must include the ^ operator in the <> operator of the variable. This would be done as follows:

array<CSquare ^> ^ sqr = gcnew array<CSquare ^>(4);

After doing this, before initializing an element, you must allocate memory for it using the gcnew operator. Here is an example:

array<CSquare ^> ^ sqr = gcnew array<CSquare ^>(4);

sqr[0] = gcnew CSquare;

After allocating memory for an element, you can access its members using the -> operator, either to display their value(s) or to change it. Here are examples:

using namespace System;

public value class CSquare
{
private:
    double sd;

public:
    CSquare() : sd(0.00) {}
    CSquare(double side) : sd(side) { }
    ~CSquare() { }

    property double Side
    {
	double get() { return sd; }
	void set(double s)
	{
	    if( s <= 0 )
		sd = 0.00;
	    else
		sd = s;
	}
    }

    property double Perimeter { double get() { return sd * 4; } }
    property double Area { double get() { return sd * sd; } }
};

int main()
{
    array<CSquare ^> ^ sqr = gcnew array<CSquare ^>(4);

    sqr[0] = gcnew CSquare;
    sqr[0]->Side = 24.55;
    sqr[1] = gcnew CSquare;
    sqr[1]->Side = 15.08;
    sqr[2] = gcnew CSquare;
    sqr[2]->Side = 8.212;
    sqr[3] = gcnew CSquare;
    sqr[3]->Side = 202.24;

    Console::WriteLine(L"Squares Characteristics");
    Console::WriteLine(L"Square 1----------");
    Console::WriteLine(L"Side:      {0}", sqr[0]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[0]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[0]->Area);

    Console::WriteLine(L"Square 2----------");
    Console::WriteLine(L"Side:      {0}", sqr[1]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[1]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[1]->Area);

    Console::WriteLine(L"Square 3----------");
    Console::WriteLine(L"Side:      {0}", sqr[2]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[2]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[2]->Area);
	
    Console::WriteLine(L"Square 4----------");
    Console::WriteLine(L"Side:      {0}", sqr[3]->Side);
    Console::WriteLine(L"Perimeter: {0}", sqr[3]->Perimeter);
    Console::WriteLine(L"Area:      {0}\n", sqr[3]->Area);

    Console::WriteLine();
    return 0;
}
 

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