#include <stdio.h>
#define LEN 10

int main ( void ) {
  int list[LEN], sum=0;
  int i, used=0;

  /* input the numbers */
  printf("Please enter some numbers, -1 to stop:\n");
  do {
    scanf("%i", &list[used]);
    used++;
  } while ( used<LEN && list[used-1]!=-1 ) ;

  /* if the user entered -1, dont count that one */
  if ( list[used-1] == -1 ) {
    used--;
  }

  /* calculate the average */
  for( i=0; i<used; i++ ) {
    sum += list[i];
  }

  /* output the average */
  printf("The average is %g.\n", (double)sum/used );

  return 0;
}