VS2019 error ：CS8370 function “ Top level statement ” stay C#7.3 Unavailable in . Please use 9.0 Or higher .

error ：

reason ： top (Top-level) The statement is in C# 9 Features added in . stay C# 9 Before , The entry point is named Main Static method of .

solve ：
In order to enable C#9.0, You need to edit .csproj File and add the following ：

<PropertyGroup>
   <LangVersion>9.0</LangVersion>
</PropertyGroup>

perhaps , You can use the following configuration to the latest C# edition （ At present, it is 11.0） Target ：

<PropertyGroup>
   <LangVersion>latest</LangVersion>
</PropertyGroup>

Open... Under the project file directory .csproj file （xml Format ）
find <PropertyGroup> Node under <LangVersion>, Change its value to 9.0.
Without this byte point , It's in <PropertyGroup> Under the node ,<WarningLevel> After node , Add... Directly <LangVersion> node ：

After reloading the project , There is no wrong report , The problem has been solved ：

The reason why the console program flashed by

problem ： In the menu bar “ start-up ” Button or press the keyboard directly “F5” key , Found that the program is running , But I haven't seen what the console shows yet , The console closes automatically .

reason ：F5 yes Debugging Pattern , In this mode , When the program is finished , The window will not remain open . and Ctrl+F5 yes Start Without Debugging Pattern , In this mode , You can see the results .

solve ： Press “Ctrl+F5” Key operation .

CS7022 The entry point of the program is the global code ; Will ignore "TestClass.Main(string[])" entry point .

problem ： If you use top-level program functions , No more Main As the entry point of the program , If you write, you won't report an error , There will be a warning , The program automatically ignores .

solve ： take Main Entry point deleted .