Sonar Sensor - C++

Hi,

I'm trying to use the sonar example in the Arduino tutorial, new Ping >> New Ping Example, when using the sonar part HC-SR04. I'm trying to use C++ here. (I can make it run fine in C.)

My problem is that I cannot seem to get the code to run correctly with my class. When I try to run the code below, I get this error,

'sonar' was not declared in this scope

I was surprised, because I thought I was declaring it, as a type 'int'.

/*
   -  Gets the distance an object is from the sonar, and sets it to variable 'distance'
   -  This variable can then be used in computations and for instructions for the robot to do something
   -    or to send it to a seperate device
*/

#include <NewPing.h>  // sonar library

class Sonar
{
  public:
  
  void Sonar_Setup()
    {
         #define TRIGGER_PIN  20  // Arduino trigger pin on sonar
         #define ECHO_PIN     21  // Arduino echo pin on sonar
         #define MAX_DISTANCE 200 /* Maximum distance we want to ping for (in centimeters). 
                                       Maximum sensor distance is rated at 400-500cm. */
                                                          
        NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.                         
    }

  void Sonar_Reading(double distance)
    {
       delay(50);    // Wait 50ms between pings (~ 20 pings/sec). 29ms should be min delay between pings
            
        Serial.print("Distance: ");
        Serial.print(distance);      // units are in inches
        Serial.println("in");
    }

  private:
  
  int uS = sonar.ping(); // Send ping, get ping time in microseconds (uS)                                               // units are converted from cm to inches
  double distance = ((uS / US_ROUNDTRIP_CM) / 2.54);  // Convert ping time to distance, 0 = outside set distance range
                                                       // units are converted from cm to inches
};

// CLASS SETUP, FORM: (  Class [space] Object  )
Sonar sonar_function;

void setup() 
{
  Serial1.begin(9600); // Open Serial1 monitor at 9600 baud to see ping results.
  sonar_function.Sonar_Setup();
}

void loop() 
{
  sonar_function.Sonar_Reading(distance);   
}

I image that's not my only issue, but I have to start somewhere. Any ideas?