if I have a schengen visa till the 10th of October 2018 for a duration of stay up to 90 days, can I travel on the 9th of October and come back 1 week after?
What is your nationality? What kind of Schengen visa do you hold?
your visa has to be valid the day you leave. so you can't enter on the 9th and exit a week later. You can exit on the 90th day.