A character is a symbol that displays on your screen. It can be a letter such as a, b, c, d, e, f, g, h, I, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, and z. It can also be a letter from A to Z. It can also be a digit such as 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. It can also by a special characters such as ` ~ # $ ! @ % ^ & * ( { [ ) } ] | \ : ; “ ‘ + - < _ ? > , / =. A character is really an integer whose value can range from -128 to 127.

To declare a character variable, you use the char keyword. Here is an example:

using namespace System;

int main()
{
	char AlphaLetter;

	Console::WriteLine();
	return 0;
}

Since a char variable represents one symbol, to initialize it, enclose the initial value in single quotes. Here are examples:

using namespace System;

int main()
{
	char AlphaLetter = 'd';
	char Pick('G');

	return 0;
}

A character variable can also be declared with the signed char data type. This type of variable would be an integer whose value can range from –128 to +127.

One of the limitations of the char data type is that it can fit only on a single character (limited to 8 bits). To support a wider range of characters, you can use the Char or the __wchar_t data types to declare a character variable. In fact, you should use either Char or __wchar_t whenever you need a character. The Char and the __wchar_t data types are defined in the System namespace. Here is an example:

using namespace System;

int main()
{
	__wchar_t AlphaLetter = 'F';

	Console::WriteLine(AlphaLetter);

	return 0;
}

This would produce:

F
Press any key to continue

Based on their structures, Char and __wchar_t variable can accommodate letters in many other languages than Latin-based. When initializing a variable declared with Char or __wchar_t, to indicate that you are using a Unicode character, you can precede the quoted value with L. Here is an example:

using namespace System;

int main()
{
	Char Letter = L'D';

	Console::WriteLine(Letter);

	return 0;
}

This would produce:

D
Press any key to continue

1. To use a character variable, change the file as follows:
    

   using namespace System; int main() { long propertyNumber = 490724; __wchar_t propertyType = 'S'; Byte stories = 2; unsigned bedrooms = 5; unsigned yearBuilt = 1962; Console::WriteLine("=//= Altair Realty =//="); Console::WriteLine("-=- Properties Inventory -=-"); Console::Write("Property #: "); Console::WriteLine(propertyNumber); Console::Write("Property Type: "); Console::WriteLine(propertyType); Console::Write("Stories: "); Console::WriteLine(stories); Console::Write("Bedrooms: "); Console::WriteLine(bedrooms); Console::Write("Year Built: "); Console::WriteLine(yearBuilt); return 0; }

2. Execute the project to see the result:
    

   =//= Altair Realty =//= -=- Properties Inventory -=- Property #: 490724 Property Type: S Stories: 2 Bedrooms: 5 Year Built: 1962 Press any key to continue . . .

3. Close the DOS window

A string is a group of characters considered as one unit, as opposed to a single character as we introduced above. Unlike some other languages such as (Object) Pascal or (Visual) Basic, C++ doesn't have a data type that can hold a group of characters as one entity. The alternative was to "create" and adapt a string data type in additional library. This problem was partially solved in a library called Standard Template Library (STL). Therefore, the STL provides the string data type.

To declare a variable that can hold a string, you can use the string data type (the string is a class but we will consider it a data type for simplicity). The value of the string must be included in double-quotes. Here is an example:

string Course = "Business Mathematics";

The string data type is part of the std namespace and it is defined in the string library. When using the string data type, make sure you include the string library and use the std namespace. To display the value of a string variable, you can use the cout extractor. Here is an example:

#include <string>
#include <iostream>
using namespace std;
using namespace System;

int main()
{
	string Course = "Business Mathematics";

	cout << Course;

	Console::WriteLine();
	return 0;
}

This would produce:

Business Mathematics
Press any key to continue

The integers we have used so far don't allow decimal values. C++ provides floating identifier values that would solve this problem. To declare a variable that involves a decimal value, you can use the float keyword. Here is an example:

using namespace System;

int main()
{
	float Fraction = 12.35;

	Console::WriteLine(Fraction);

	Console::WriteLine();
	return 0;
}

A float variable can hold a number that ranges from 3.4 x 10^-38 to 3.4 x 10³⁸. Besides, or instead of, float, you can use the Single data type to declare a variable that holds a simple decimal value. The Single data type is defined in the System namespace.

1. To declare a single-precision variable, change the file as follows:
    

   using namespace System; int main() { long propertyNumber = 490724; __wchar_t propertyType = 'S'; Byte stories = 2; unsigned bedrooms = 5; float bathrooms = 3.5; unsigned yearBuilt = 1962; Console::WriteLine("=//= Altair Realty =//="); Console::WriteLine("-=- Properties Inventory -=-"); Console::Write("Property #: "); Console::WriteLine(propertyNumber); Console::Write("Property Type: "); Console::WriteLine(propertyType); Console::Write("Stories: "); Console::WriteLine(stories); Console::Write("Bedrooms: "); Console::WriteLine(bedrooms); Console::Write("Bathrooms: "); Console::WriteLine(bathrooms); Console::Write("Year Built: "); Console::WriteLine(yearBuilt); return 0; }

2. Execute the project to see the result:
    

   =//= Altair Realty =//= -=- Properties Inventory -=- Property #: 490724 Property Type: S Stories: 2 Bedrooms: 5 Bathrooms: 3.5 Year Built: 1962 Press any key to continue . . .

3. Close the DOS window

One of the limitations of the float data type is that it provides less precision than required sometimes (in fact, the Microsoft C++ compiler, always displays a warning when you use the float data type to declare a variable). The alternative is to use the double keyword or the Double data type to declare a variable that would hold decimal numbers. The Double data type is defined in the System namespace.

A double-precision variable declared with double or Double can hold a decimal or fractional number that ranges from 1.7 x 10^-308 to 1.7 x 10³⁰⁸. It is used for numbers that and/or are very large.

using namespace System;

int main()
{
	System::Double Fraction = 12.35;

	Console::WriteLine(Fraction);

	return 0;
}

This would produce:

12.35
Press any key to continue

1. To use a double-precision variable, change the file as follows:
    

   using namespace System; int main() { long propertyNumber = 490724; __wchar_t propertyType = 'S'; Byte stories = 2; unsigned bedrooms = 5; float bathrooms = 3.5; unsigned yearBuilt = 1962; double marketValue = 652540; Console::WriteLine("=//= Altair Realty =//="); Console::WriteLine("-=- Properties Inventory -=-"); Console::Write("Property #: "); Console::WriteLine(propertyNumber); Console::Write("Property Type: "); Console::WriteLine(propertyType); Console::Write("Stories: "); Console::WriteLine(stories); Console::Write("Bedrooms: "); Console::WriteLine(bedrooms); Console::Write("Bathrooms: "); Console::WriteLine(bathrooms); Console::Write("Year Built: "); Console::WriteLine(yearBuilt); Console::Write("Market Value: "); Console::WriteLine(marketValue); return 0; }

2. Execute the project to see the result:
    

   =//= Altair Realty =//= -=- Properties Inventory -=- Property #: 490724 Property Type: S Stories: 2 Bedrooms: 5 Bathrooms: 3.5 Year Built: 1962 Market Value: 652540 Press any key to continue . . .

3. Close the DOS window

You may have found out that when you declare and initialize a float or Single variable, the compiler generates a warning. Consider the following example:

using namespace System;

int main()
{
	float Fraction = 12.35;

	Console::WriteLine(Fraction);

	Console::WriteLine();
	return 0;
}

When compiled, you would get the following warning:

.\Exercise.cpp(5) : warning C4305: 'initializing' : truncation from 'double' to 'float'

Although the program would compile fine. By default, when the compiler sees a value such as 12.35, for the sake of precision, it tends to store it as a double value. If you really want the variable to be treated as a float or Single, add the f or F to its right. Here is an example:

using namespace System;

int main()
{
	float Fraction = 12.35f;

	Console::WriteLine(Fraction);

	Console::WriteLine();
	return 0;
}

This time, the compiler will not generate a warning. Remember that you can use f (lowercase) or F (uppercase).

The data types we have used so far may have names we are not familiar with. C++ allows you to customize the name of a data type to a name you are more familiar with. You would not (and are not allowed to) create a new data type, you would only "redefine" the name of an existing data type.

To customize the name of a data type, you can use the typedef keyword. The formula used is:

typedef KnownDataType NewName;

The typedef keyword is required to let the compiler know that you are creating a new data type. The data type must be one that exists already, such as those we have reviewed so far. It could be an int, an unsigned int, an Int32, a char, a double, etc. An example of using a typedef is:

using namespace System;

int main()
{
	typedef unsigned int PositiveNumber;

	return 0;
}

In this case, PositiveNumber is just a new name for an unsigned int. It can be used as a new data type exactly as if you were using an unsigned int. Here are examples:

using namespace System;

int main()
{
	typedef unsigned int PositiveNumber;
	typedef double	   Salary;

	PositiveNumber Gender   = 1;
	Salary WeeklySalary     = 1450.88;

	Console::Write("Gender: ");
	Console::WriteLine(Gender);
	Console::Write("Salary: ");
	Console::WriteLine(WeeklySalary);

	return 0;
}

This would produce:

Gender: 1
Salary: 1450.88
Press any key to continue . . .

A reference is a variable that is a duplicate of an existing variable. It provides a technique of creating more than one name to designate the same variable. The syntax of creating or declaring a reference is:

DataType &ReferenceName = VariableName;

To declare a reference, type the variable’s name preceded by the same type as the variable it is referring to. Between the data type and the reference name, type the ampersand operator “&”. To specify what variable the reference is addressed to, use the assignment operator “=” followed by the name of the variable. The referred to variable must exist already. You cannot declare a reference as:

int &Mine;

The compiler wants to know what variable you are referring to. Here is an example:

using namespace System;

int main()
{
	int Number = 228;
    	int &Nbr = Number;
	
	Console::WriteLine(Number);
	Console::WriteLine(Nbr);

	return 0;
}

The ampersand operator between the data type and the reference can assume one of three positions as follows:

int& Nbr;
int & Nbr;
int &Nbr;

As long as the & symbol is between a valid data type and a variable name, the compiler knows that the variable name (in this case Nbr) is a reference.

Once a reference has been initialized, it holds the same value as the variable it is pointing to. You can then display the value of the variable using either of both:

#include <iostream>

using namespace std;
using namespace System;

int main()
{
	int Number = 228;
	int &Nbr = Number;
	
	cout << "Number:        ";
	Console::WriteLine(Number);
	cout << "Its reference: ";
	Console::WriteLine(Nbr);
	
	Console::WriteLine();
	return 0;
}

This would produce:

Number:        228
Its reference: 228

Press any key to continue

If you change the value of the variable, the compiler updates the value of the reference so that both variables would hold the same value. In the same way, you can modify the value of the reference, which would update the value of the referred to variable. To access the reference, do not use the ampersand operator; just the name of the reference is sufficient to the compiler. This is illustrated in the following:

#include <iostream>

using namespace std;
using namespace System;

int main()
{
	int Number = 228;
    	int &Nbr = Number;
	
	cout << "Number:        ";
	Console::WriteLine(Number);
	cout << "Its reference: ";
	Console::WriteLine(Nbr);
	
	Number = -15008;
	
	cout << "\nNumber:        ";
	Console::WriteLine(Number);
	cout << "Its reference: ";
	Console::WriteLine(Nbr);

	Number = 28114;
	
	cout << "\nNumber:        ";
	Console::WriteLine(Number);
	cout << "Its reference: ";
	Console::WriteLine(Nbr);

	Console::WriteLine();
	return 0;
}

This would produce:

Number:        228
Its reference: 228

Number:        -15008
Its reference: -15008

Number:        28114
Its reference: 28114

Press any key to continue

It is very important to remember the relationship that a variable in the stack has with its value: A variable in the stack contains its own value. Whenever you access this variable, it gives you copy of its value and retains the original. Once you have that value, you can do what you want with it and this would not have any impact on the variable itself or its value. For example, if you assign such a value to another variable, that other variable receives its own copy. Let's illustrate with the following program:

#include <iostream>

using namespace std;
using namespace System;

int main()
{
    	// TODO: Please replace the sample code below with your own.
	int Number1 = 255;
	int Number2 = Number1;

	Console::WriteLine(Number1);
	Console::WriteLine(Number2);
	
    	Console::WriteLine();
	return 0;
}

This would produce:

255
255

Press any key to continue

Notice that when the value of the first variable has been assigned to the second variable both variables hold the same value. With another assignment, you can change the value of the second variable and the first would keep its value:

#include <iostream>

using namespace std;
using namespace System;

int main()
{
    	// TODO: Please replace the sample code below with your own.
	int Number1 = 255;
	int Number2 = Number1;

	Console::WriteLine(Number1);
	Console::WriteLine(Number2);
	Console::WriteLine();
	
	Number2 = -48;

	Console::WriteLine(Number1);
	Console::WriteLine(Number2);
    	Console::WriteLine();
	return 0;
}

This would produce:

255
255

255
-48

Press any key to continue

This comparison is important because its sets apart the references as we saw above. This will be even more important with pointers in the next lesson.

If you create a C++ reference as done above, the variable is stored in the stack. When the program ends, the compiler reclaims the memory the variable was using. The C++/CLI language provides another way to declare such a reference. In this case, the CLR garbage collector would be able to reclaim the memory that the variable was using. This type of  variable is called a tracking reference.

To create a tracking reference, use the percent operator "%" instead of the ampersand. Here is an example:

int main()
{
	int % PropertyValue;

	return 0;
}

Like a native reference, in order to use a tracking reference, you must initialize it with a variable that has been declared and initialized appropriately. Here is an example:

using namespace System;

int main()
{
	double Value = 468550;
	double % PropertyValue = Value;

	Console::Write("Property Value = $");
	Console::WriteLine(Value);
	Console::Write("Property Value = $");
	Console::WriteLine(PropertyValue);

	return 0;
}

After creating a tracking reference, if you change the value of the variable, the value of the tracking reference would be changed also. If you update the value of the tracking reference, the value of the variable would be updated also.