A1 Not Declared in this scope

Hi:
I’ve got a question about a problem I’m having. I don’t know why it is ok to use A0 in the sketch and it compiles correctly but when I use A1 as the analog input I get a message that A1 is not declared in this scope. I hope it is easy but I certainly need your help. Note in the code that I’ve changed A0 to A1. I did this because in a PID program I’m working on I need both A0 and A1. The code is

/*
  Analog Input

  Demonstrates analog input by reading an analog sensor on analog pin 0 and
  turning on and off a light emitting diode(LED) connected to digital pin 13.
  The amount of time the LED will be on and off depends on the value obtained
  by analogRead().

  The circuit:
  - potentiometer
    center pin of the potentiometer to the analog input 0
    one side pin (either one) to ground
    the other side pin to +5V
  - LED
    anode (long leg) attached to digital output 13
    cathode (short leg) attached to ground

  - Note: because most Arduinos have a built-in LED attached to pin 13 on the
    board, the LED is optional.

  created by David Cuartielles
  modified 30 Aug 2011
  By Tom Igoe

  This example code is in the public domain.

  http://www.arduino.cc/en/Tutorial/AnalogInput
*/

int sensorPin = A1;    // select the input pin for the potentiometer
int ledPin = 13;      // select the pin for the LED
int sensorValue = 0;  // variable to store the value coming from the sensor

void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);
  // turn the ledPin on
  digitalWrite(ledPin, HIGH);
  // stop the program for <sensorValue> milliseconds:
  delay(sensorValue);
  // turn the ledPin off:
  digitalWrite(ledPin, LOW);
  // stop the program for for <sensorValue> milliseconds:
  delay(sensorValue);
}

Which board do you have selected from the Arduino IDE's Tools > Board menu?

Thank you so much. I'm using the UNO on this project and I had last set the board as the ESP32; I've been playing with it. Your advice has saved me much time and sweat. Thank you much. Bob

You're welcome. I'm glad to hear you found the problem. Thanks for taking the time to post an update with your solution. Enjoy! Per