Solve the problem of compilation error when creating .net standard class library in Visual Studio 2017

C# is a modern, object-oriented programming language developed by Microsoft and as part of the .NET framework. 1.C# supports object-oriented programming (OOP), including encapsulation, inheritance and polymorphism. 2. Asynchronous programming in C# is implemented through async and await keywords to improve application responsiveness. 3. Use LINQ to process data collections concisely. 4. Common errors include null reference exceptions and index out-of-range exceptions. Debugging skills include using a debugger and exception handling. 5. Performance optimization includes using StringBuilder and avoiding unnecessary packing and unboxing.

Testing strategies for C#.NET applications include unit testing, integration testing, and end-to-end testing. 1. Unit testing ensures that the minimum unit of the code works independently, using the MSTest, NUnit or xUnit framework. 2. Integrated tests verify the functions of multiple units combined, commonly used simulated data and external services. 3. End-to-end testing simulates the user's complete operation process, and Selenium is usually used for automated testing.

C#.NET is still important because it provides powerful tools and libraries that support multiple application development. 1) C# combines .NET framework to make development efficient and convenient. 2) C#'s type safety and garbage collection mechanism enhance its advantages. 3) .NET provides a cross-platform running environment and rich APIs, improving development flexibility.

C#.NETisversatileforbothwebanddesktopdevelopment.1)Forweb,useASP.NETfordynamicapplications.2)Fordesktop,employWindowsFormsorWPFforrichinterfaces.3)UseXamarinforcross-platformdevelopment,enablingcodesharingacrossWindows,macOS,Linux,andmobiledevices.

C#.NETissuitableforenterprise-levelapplicationswithintheMicrosoftecosystemduetoitsstrongtyping,richlibraries,androbustperformance.However,itmaynotbeidealforcross-platformdevelopmentorwhenrawspeediscritical,wherelanguageslikeRustorGomightbepreferable.

C# is widely used in enterprise-level applications, game development, mobile applications and web development. 1) In enterprise-level applications, C# is often used for ASP.NETCore to develop WebAPI. 2) In game development, C# is combined with the Unity engine to realize role control and other functions. 3) C# supports polymorphism and asynchronous programming to improve code flexibility and application performance.

The programming process of C# in .NET includes the following steps: 1) writing C# code, 2) compiling into an intermediate language (IL), and 3) executing by the .NET runtime (CLR). The advantages of C# in .NET are its modern syntax, powerful type system and tight integration with the .NET framework, suitable for various development scenarios from desktop applications to web services.

C# and .NET adapt to the needs of emerging technologies through continuous updates and optimizations. 1) C# 9.0 and .NET5 introduce record type and performance optimization. 2) .NETCore enhances cloud native and containerized support. 3) ASP.NETCore integrates with modern web technologies. 4) ML.NET supports machine learning and artificial intelligence. 5) Asynchronous programming and best practices improve performance.