// TEST: can a bug in the code issue a change in the simulation beviour ?
//
// Trying to write faulty code that makes a difference
// between a button click with the mouse or with the keyboard.
//
// Conclusion: No, that is not possible for an Arduino Uno

unsigned long counter = 0;
int oldValue = HIGH;

char buffer_before[8];
char buffer[8];
char buffer_after[8];

void setup() 
{
  Serial.begin(115200);
  pinMode(2,INPUT_PULLUP);

  // fill the buffers
  memset(buffer,'X',8);
  memset(buffer_before,'#',8);
  memset(buffer_after,'*',8);
}

void loop() 
{
  int value = digitalRead(2);
  if(value != oldValue)
  {
    counter++;
    ultoa(counter,buffer-2,10);  // BUG
    // Remove the zero terminator
    int n = strlen(buffer);
    buffer[n] = '=';  // BUG
    Serial.print(buffer);
    Serial.print(buffer_before);
    Serial.println(buffer_after);

    oldValue = value;
  }
}