VS2017 implicitly typed local variables are not available in C-sharp2?

VS2017 Enterprise Edition, var do not recognize? How to upgrade C-sharp?
No problem generating DLL.

Vs2017 c-sharp
Mar.22,2021

(1) right-click the current project, click "Properties]
(2) Click" generate "in the left Tab, and click" Advanced "in the lower right corner of the interface.
(3) modify the language version

requires C-sharp3 or higher version

right-click the project, and then select" Properties ". In the pop-up Properties dialog box, In the 'applications' tab, change the. NET Framework version of the current project to version 3.0 or above.

Previous: QQ scan interface function does not work

Next: Why IDEA prompts unchecked cast operation, I add @ SuppressWarnings to save and delete automatically

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e4d794-44f25.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e4d794-44f25.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?