// constants won't change
const int buttonPin = 25; 
const int LEDPin    = 26; 

int ledState = LOW;    
int lastButtonState;    
int currentButtonState; 
void setup() {
  Serial.begin(9600);                
  pinMode(buttonPin, INPUT_PULLUP); 
  pinMode(LEDPin, OUTPUT);          
  currentButtonState = digitalRead(buttonPin);
}
void loop() {
  lastButtonState    = currentButtonState;     
  currentButtonState = digitalRead(buttonPin); 
  if(lastButtonState == HIGH && currentButtonState == LOW) {
    Serial.println("The button is pressed");
  
    ledState = !ledState;
  
    digitalWrite(LEDPin, ledState); 
  }
  delay(100);
}