Also see
https://www.arduino.cc/en/Tutorial/BuiltInExamples/Button
Your switch inputs are floating. From the tutorial:
"If you disconnect the digital I/O pin from everything, the LED may blink erratically. This is because the input is "floating" - that is, it will randomly return either HIGH or LOW. That's why you need a pull-up or pull-down resistor in the circuit".