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Hello.

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In this video, we're going to talk about Question 49, what are preprocessor directives preprocessor

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directives?

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Help us control the compensation process from the level of the code itself.

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You can choose if some part of the code will be compiled or not.

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We can disable or enable some compensation warnings, or we can even check for the doesnAt version and

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execute different code, depending on it.

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But first, what is a pre process or a preprocessor also known as the pre compiler?

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Is the program that runs before the actual compiler that can apply some operations on code before it's

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compiled.

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Although the C-sharp compiler doesn't have a separate preprocessor, the directives we'll talk about

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in this lecture are processed as if there were one.

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We can recognize preprocessor directives by the fact that they start with the hash symbol preprocessor

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directive must be the only code in a line.

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Let's see some of the most useful preprocessor directives in C-sharp.

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In the last lecture, we mentioned the if debug and if released directives would allow us to include

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some called into compilation only if you are in debug or release mode.

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When writing preprocessor directives, we can use hash if hash elif and Hash Alice directives to control

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what we want to compile.

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Logically, they work the same as the if else, if and other statements.

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Besides checking for debug or release mode, we can also take things like the version of dotNet or the

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UP target, like iOS or Android.

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Let's see this in code.

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As you can see here, we built a pretty complex logic, depending on the build mode and the application

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target.

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Those directives are very useful when we build an application that targets more than one version or

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easements to work on different platforms.

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Another commonly used preprocessor directive is Hot Region Region allows us to define our region of

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code that can be collapsed in Visual Studio.

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So it doesn't affect the actual compilation process.

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And now we can collapse those lines.

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Returns are often used without the generated code that we don't really want to read that often.

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Some developers defined regions large files, so some parts of them can be collapsed, making the file

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seem smaller and easier to read.

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I wouldn't recommend that as this is simply sweeping the problem of a large class under the rug refactoring

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is definitely a better approach.

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We can also use error and wording we process or directives to explicitly create a compliance warning

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or let's say we want to raise a warning when this method is used.

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And here is the warning we created the same way.

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We could also create errors that would include the compensation process to finish.

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Speaking of warnings.

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We can disable some of them in a file using another preprocessor directive pragma warning disable.

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Let's consider this code, as we learned in the what is the difference between throw and throw x lecturer?

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Should rather you stroll instead of throw x, the compiler actually warns us, If we do this mistake,

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please pay attention to this warning code.

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US will need it in a second.

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If you are 100 percent sure what we are doing, we can disable this warning in the code using harsh

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pragma warning disable.

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As you can see, we must specify the type of warning by its code, and now the warning is gone from

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the warnings list.

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Pragma warning disable disables the warning until the end of the file, so it is a good practice to

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restore it after the last line.

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It should affect.

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All right.

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We worried about some, but not all preprocessor directives.

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Easy, sharp.

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As you can see, they can be pretty useful when it comes to controlling what code is compiled under

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given the circumstances or what warnings should be shown.

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If you want to read about all available pre-processed or directives, make sure to check out the article

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I linked in the resources attached to this lecture.

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In the next lecture will learn about one more preprocessor directive.

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If this topic comes up during the interview, you can be asked What is the preprocessor?

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A preprocessor, also known as the compiler, is a program that runs before the actual compiler, and

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it applies some operation on code before the compilation starts.

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How to disable selected warning in a file by using the pragma warning disable preprocessor directive,

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it takes the warning code as the parameter.

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So, for example, to disable the don't use strokes warning, we can write hush pragma warning disable

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see 22 zero zero as this is the code of this warning.

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All right, that's it in this video.

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Thanks for watching and see you in the next one.