# C# Preprocessor

# Error and Warning

* `#error`: Invoke compiler error with message
    
* `#warning`: Invoke compiler warning with message
    

```csharp
#warning This is warning
#error This is error
```

**Output**

Because of error directive, `dotnet build Program.cs` will print below output.

```bash
$ dotnet build .\Program.cs
MSBuild version 17.6.0-preview-23122-01+4b5e303b3 for .NET
C:\Users\archdsp\Projects\HelloWorld\Program.cs(1,1): error MSB4025: The project file could not be loaded. Data at the root level is invalid. Line 
1, position 1.

Build FAILED.

C:\Users\archdsp\Projects\HelloWorld\Program.cs(1,1): error MSB4025: The project file could not be loaded. Data at the root level is invalid. Line 
1, position 1.
    0 Warning(s)
    1 Error(s)
```