int oldSensVal = 1; //initialize sensor value 
int count = 0; //initialize count of magnet passes 

void setup() {
  Serial.begin(9600); //start serial communication
}

void loop() {
  int sensorValue = digitalRead(2);  //read sensor value, save as 'sensorValue'
  if (sensorValue==0){  //if sensor value is 0, i.e. detects magnet
    Serial.print("magnet");  //..print 'magnet'
    if (sensorValue!=oldSensVal){  //if the sensor value has just changed
      count++;  //count that as an additional count for magnet passed
    }
  }
  else{  //otherwise..
    Serial.print(sensorValue);  //print the sensor Value (0 or 1)
  }
  Serial.print("-");
  Serial.println(count); //display the total count of magnet passes
  delay(10);  //delay period (ms)
  oldSensVal = sensorValue;  //set currentvalue as the previous value 
}