#include <stdio.h>
#include <string.h>

typedef struct
{
  double average;
  int count;
}
stats_type;

static void
testc (stats_type *s, long long data)
{
  s->average = (s->average * s->count + data) / (s->count + 1);
  s->count++;
}

int
main (void)
{
  stats_type s;
  
  s.average = 0;
  s.count = 0;
  testc (&s, 10);
  testc (&s, 20);
  printf ("%g %d\n", s.average, s.count);
  return 0;
}