C# 5.0 Programmer's Reference

Preprocessor Directives ❘ 31
The second tab opens Team Explorer, a tool that helps you manage
your work in a team environment. For more information, see
msdn.microsoft.com/library/hh500420.aspx.
The third tab opens the Class View. This tool enables you to view
the classes defined by your projects. You can expand the classes to
learn about their inheritance hierarchies. If you click a class, the bottom
of the window shows you the class’s properties, methods, and
events. If you double-click one of these items, Visual Studio opens
the code that defines it in the Code Editor.
Figure 3-4 shows the Class View displaying information about the
Turtle class defined in the TurtleLib project.
Some projects may have other hidden files. For example, when you
add controls to a form, the designer adds a resource file to the form
to hold any resources needed by the controls.
Normally, you do not need to work directly with the hidden files,
and doing so can mess up your application. At best, the changes
you make will be lost. At worst, you may confuse Visual Studio, so
it can no longer load your project.
Instead you should use other tools to modify the hidden files
indirectly. For example, the files holding resources used by a
form are automatically updated when you modify the form and
its controls.
Figure 3-4: The Class View
lets you examine the classes
defined by a project.
Preprocessor Directives
Preprocessor directives are commands for the C# compiler. They tell the compiler such things as
which pieces of code to include in compilation and how the Code Editor should group lines of code.
The following sections describe the most useful C# preprocessor directives.
#define and #undef
The #define directive defines a preprocessor symbol that you can then use with the #if, #else,
#elif, and #endif directives described next. Preprocessor symbols are either defined or not defined.
They do not have values like constants inside the code do.
NOTE A program can create variables and constants with the same names as
defined preprocessor symbols.
The #undef directive removes the definition of a defined symbol.
The #define and #undef directives must come before any programming statements including using
directives. They apply for the entire file that contains them.
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