One 、 Why it went wrong ？

        C Functions in languages are unsafe . In the use of scanf Function time , The space occupied by the data to be placed is not detected （ Data may be out of bounds ）, So this is not safe enough .VS Although the scanf_s function , But this is VS Function of , instead of C Functions of language , If you use scanf_s function , The portability of the code will be reduced , So... Is not recommended VS Function of .

Two 、 How to solve ？

1. Temporary settlement

  Add   #define _CRT_SECURE_NO_WARNINGS 1      after , Compile and run .

2. Permanent solution

stay VS Found in the installation directory newc++file.cpp file , If you can't find it , Specific documents , You can enter the installation directory first , Then use explorer to search （ It will be found soon ）.

Right click Click on -> attribute   Modify file permissions .

  Open in Notepad , Join in  #define _CRT_SECURE_NO_WARNINGS 1      after , preservation .

After preservation , To create a C Source file , Will be automatically added   #define _CRT_SECURE_NO_WARNINGS 1