Passing Variable Number of Arguments to a Function Call (C++)

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C++

I am trying to Pass A Variable number of Arguments to a Function. I have read code from Ivor Horton's "Beginning C++ 2005" and searched online but all examples pass the variables through code, However I want the variables to be passed from user input (The code should not know How many variables are passed Until the user enters them). I Hope You guys get Me.

I have written a simple program to calculate the Average of numbers the user enters, it stores them in an array. Now I want the Items in the array to be read as arguments to the function.

I know there are better ways of implementing the Averages, but my emphasis is on learning the concept of Passing Variable Number of Arguments to a Function. Below is My code, which works fine, and accepts input from the user, storing given numbers in an array, up to 20 numbers. I want to pass on these numbers to the averages function, also defined.

//Find the average of Numbers
//Demonstrates the Passing a variable number of Arguments to a Function Call

#include <iostream>
#include <string>
#include <sstream>
#include "stdarg.h"

using namespace std;

double averages(int count,...);//Prototype for the Function

int main()
{
 
      
 	double Number = 0.00;//Instantiate a double precision floating point valuable
 	int count = 0;//integer to keep count of user entries
 	string input = "";//string to get input from the user
 	double Numbers[20]; //Array to store User entered Numbers
 	
	 while ((input !="x") && (input !="X") && (count <20)) //Unless user Enters 'X' or 20 Numbers, store the number and ask for another
 	{
	 	while(true)
	 	{
		 		   
	     cout<<"Please Enter a Given Number: ";
		 getline(cin,input);//Get user input
		 
		 if((input=="X")||(input=="x"))//If User entered X, break (since loop doesn't run if input is X . . . .)
		 { 
		   cout <<endl<<"You Ended The Sequence";
		   break;
	     }
	     
		 stringstream mystream(input);
		 
		 if (mystream >> Number)//If User enters a Valid number, break 
		  break;
	     cout<<"Invalid Number, Please Try Again";
	     
		 }
		 
    Numbers[count] = Number; //Store currently entered Number in relevant Position in the array
	count++; //Increment the Counter
		 
    }
}

double averages(int count, ...)
{
 	   if (count<=0)//If count is not a whole number greater than zero, return 0.0 as the average
 	   {return 0.0;}
 	   
 	   va_list plist; //Declare a Pointer to the Argument List
 	   va_start(plist,count);
 	   
 	   //First Calculate the sum
 	   double sum = 0.0;//Declare Double Precision floating point Number to store sum of all numbers
 	   
 	   for(int i=0;i<count;i++)
 	   {
	     sum += va_arg(plist, int);//For each of the numbers, add it to the sum
	   }
	   
	   va_end(plist);//Reset the Pointer to Null
	   
	   double avg = sum/count;//Declare Double Precision floating point Number and assign it the value Sum/Count i.e Average
	   
	   return avg;//Return the average
}