Hi,
About PULL UP or PULL DOWN resistors used along with Switches.
Switch is connected to an input pin of Microcontroller. A pin is in input state means that it is in HIGH IMPEDANCE state. So if you don’t connect any PULL UP or PULL DOWN resistors that pin will remains FLOATING when the switch is in OFF state. A floating pin may catch noises and reading such a pin will result in unexpected results. Its value usually varies erratically varies.
Programming Language
It is C.