C #if

In C#, the #if directive is used for conditional compilation. It allows you to include or exclude certain sections of code during the compilation process based on specified conditions. The #if directive is evaluated by the preprocessor, which determines whether the specified condition is true or false.

The basic syntax of the #if directive is as follows:

#if condition
    // code to include if the condition is true
#else
    // code to include if the condition is false
#endif

The condition in the #if directive can be any valid expression that evaluates to a boolean value. It can include predefined symbols, such as DEBUG, which is commonly used to include debugging code that should only be present in debug builds.

Here’s an example that demonstrates the usage of #if directive:

#define DEBUG

using System;

public class Program
{
    public static void Main()
    {
        #if DEBUG
            Console.WriteLine("Debug mode is enabled.");
        #else
            Console.WriteLine("Debug mode is disabled.");
        #endif
    }
}

In this example, the DEBUG symbol is defined using the #define directive at the beginning. When the code is compiled, the #if DEBUG condition is true, and the message “Debug mode is enabled.” will be displayed. If the DEBUG symbol is not defined or is commented out, the #if DEBUG condition would be false, and the message “Debug mode is disabled.” would be displayed.

By using #if directives, you can conditionally include or exclude code sections based on the desired compilation configuration, making it useful for creating different build variants or handling platform-specific code.