const int switchPin = 2; // the number of the switch pin
const int relay = 4; // the number of the relay
int switchState = 0;
 
void setup()
{
 Serial.begin(9600);
 pinMode(switchPin, INPUT);
 pinMode(relay, OUTPUT);
}
 
void loop()
{
 switchState = digitalRead(switchPin);
 if (switchState == HIGH)
 {
  digitalWrite(relay, HIGH); delay(100);
 }
 else
 {
  digitalWrite(relay, LOW);
 }
}