const int greenLedPin = 10;
const int redLedPin = 12;
const int buttonPin = 2;

bool isGreenOn = true;
bool buttonState = false;
bool lastButtonState = false;

void setup() {
  pinMode(greenLedPin, OUTPUT);
  pinMode(redLedPin, OUTPUT);
  pinMode(buttonPin, INPUT);

  digitalWrite(greenLedPin, HIGH);
  digitalWrite(redLedPin, LOW);
}

void loop() {
   buttonState = digitalRead(buttonPin);

   if (buttonState == LOW && lastButtonState == LOW) {
     if (isGreenOn == true) {
       (isGreenOn = false);
     } else {
       (isGreenOn = true);
     }

     if (isGreenOn == true) {
       digitalWrite(greenLedPin, HIGH);
       digitalWrite(redLedPin, LOW);
     } else {
       digitalWrite(greenLedPin, LOW);
       digitalWrite(redLedPin, HIGH);
     }

     delay(50);
   }

   lastButtonState = buttonState;
}