#include <Arduino.h>
#include <stdio.h>

int Add(int num, ...) {
  int valu, total = 0;

  //Declare a va_list macro and initialize it with va_start
  va_list argList;
  va_start(argList, num);

  for(; num; num--) {
    valu = va_arg(argList, int);
    Serial1.print("valu: "); Serial1.print(valu, DEC);

    total += valu;

    Serial1.print("  total: "); Serial1.println(total);
  }  
  va_end(argList);
  return total;
}

void setup() {
  Serial1.begin(9600);
  while (!Serial1);
  Serial1.println(Add(3,2,3,4));  //first arg is number of subsequent variables
}

void loop() { delay(1); }