C# 0 The Complete Reference

Building

 and 

BuildingDemo

. Inside 

BuildingDemo

,

the

Main( )

 method creates an instance of 

Building

 called 

house

. Then the code within 

Main( )

 accesses the instance variables associated with 

house

, assigning them values and 

using those values. It is important to understand that 

Building

 and 

BuildingDemo

 are two 

separate classes. The only relationship they have to each other is that one class creates an 

instance of the other. Although they are separate classes, code inside 

BuildingDemo

 can 

access the members of 

Building

 because they are declared 

public

. If they had not been 

given the 

public

 access specifier, their access would have been limited to the 

Building

class, and 

BuildingDemo

 would not have been able to use them.

Assume that you call the preceding file 

UseBuilding.cs

. Compiling this program creates 

a file called 

UseBuilding.exe

. Both the 

Building

 and 

BuildingDemo

 classes are automatically 

part of the executable file. The program displays the following output:

house has:

  2 floors

  4 occupants

  2500 total area

  625 area per person

It is not necessary for the 

Building

 and the 

BuildingDemo

 classes to actually be in 

the same source file. You could put each class in its own file, called 

Building.cs

 and 

BuildingDemo.cs

, for example. Just tell the C# compiler to compile both files and link 

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