My roper washing machine wont stop filling, water just keeps running until it runs over the top of tub and onto floor. I was just wondering if the switch controls the water level of is there something on the tub itself.

If when you shut off or unplug the machine, the water stops response #1 is correct.
If shutting it off or unplgging it, doesn't work and you have to shut the water off at the shut off valves, the dual water valve is bad.

If you open the cabinet yoiu should find a tube off the side its a vaccum tube in a way,,,
as the tub fills up the air int he tube is compressed by the water,,, that pressure then triggers a "pressure switch in side your control panal....
what you will need to determine if there is a leak in the tube or is the pressure switch bad........