bool

1int LEDpin = 5;     // LED on pin 5
2    int switchPin = 13; // momentary switch on 13, other side connected to ground
3
4    bool running = false;
5
6    void setup() {
7      pinMode(LEDpin, OUTPUT);
8      pinMode(switchPin, INPUT);
9      digitalWrite(switchPin, HIGH);  // turn on pullup resistor
10    }
11
12    void loop() {
13      if (digitalRead(switchPin) == LOW) {
14        // switch is pressed - pullup keeps pin high normally
15        delay(100);                     // delay to debounce switch
16        running = !running;             // toggle running variable
17        digitalWrite(LEDpin, running);  // indicate via LED
18      }
19    }