void setup()
{
  pinMode(3,INPUT); //switch pin
  pinMode(7,OUTPUT); // LED pin
}
 
void loop()
{
 
  while( digitalRead(3) == 1 ) //while the button is pressed
  {
    //blink
    digitalWrite(7,HIGH);
    delay(1000);
    digitalWrite(7,LOW);
    delay(1000);
  }
}