Do I need to show my cards

[MARK R]

This is the situation.

On the river only two players remain.
A guy makes a bet I call the bet the other guy instant mucks his cards and says you win. I am the only person left at the table with cards. Do I need to show my cards to claim the pot. I asked the floor person on the night who said I had to show my cards. The next night I asked the head floor person who said I do not need to show my cards. What is the correct rule in other places.

Mark.