How to use the conditional instruction of C #

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Conditional instruction

You can use the # if directive to create a conditional directive. Conditional instructions are used to test whether the symbol is true. If true, the compiler executes the code between # if and the next instruction.

Syntax for conditional instructions:

# if symbol [operator symbol]...

Where symbol is the name of the symbol to be tested. You can also use true and false, or place negative operators before symbols.

Common operators are:

= (equal to)

! = (not equal to)

& (and)

| | (or)

You can also group symbols and operators in parentheses. Conditional directives are used to compile code when debugging a version or when compiling a specified configuration. A conditional instruction that begins with a # if instruction must be explicitly terminated with a # endif instruction.

The following program demonstrates the use of conditional instructions:

# define DEBUG

# define VC_V10

Using System

Public class TestClass

{

Public static void Main ()

{

# if (DEBUG & &! VC_V10)

Console.WriteLine ("DEBUG is defined")

# elif (! DEBUG & & VC_V10)

Console.WriteLine ("VC_V10 is defined")

# elif (DEBUG & & VC_V10)

Console.WriteLine ("DEBUG and VC_V10 are defined")

# else

Console.WriteLine ("DEBUG and VC_V10 are not defined")

# endif

Console.ReadKey ()

}

}

When the above code is compiled and executed, it produces the following results:

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