`"C:\xampp\mysql\bin"' is not recognized as an internal or external command,operable program or batch file
You might want to try the following instead: 

C:\xampp\mysql\bin\mysql.exe -u root -p


assuming you are using a CMD / DOS Prompt

Depending on the path in which your mysql.exe resides, you might have to incorporate using double quotes as follows:

""C:\Program Files (x86)\mysql\bin\mysql.exe" -u root -p"


assuming you are using a CMD / DOS Prompt

You add double-quotes from "C:\... to the end of the executable ...exe" and then add double-quotes at the beginning of the whole command until the end. You end up with the above command.

Reference: Long Filenames or Paths with Spaces Require Quotation Marks (Microsoft Support)