error: EPERM : operation not permitted, mkdir C:\ code example

Example: Error:....... EPERM: operation not permitted, mkdi

Open Terminal
Go to c:/users and run dir /x 
check shorter name of your usernsme you found with dir/x 
//In my case my username is Nandini Jain and I got short id= NANDIN~1
and run npm config set cache "C:/Users//AppData/Roaming/npm-cache" --global
//I ran the command
//C:/Users/NANDIN~1/AppData/Roaming/npm-cache" --global

HOPE THIS WILL WORK BECAUSE ITS THE ONLY REASON OF YOUR QUERY.