triangle numbers no ifs

noif.c

#include <stdio.h>
/* to compile
 * cc noif.c -o noif
 *
 * Usage: ./noif
 *        ./noif <N> 
 *    where <N> is an integer.*/
fn(int n){  ((n>0) && (n = fn(n-1)+n)) || (n = 0);  return n; }

main(int argc, char *argv[]){
  int n;
  ((argc > 1) && sscanf(argv[1], "%d", &n)) || /*for reading from command line*/
    (printf("number: "),  scanf("%d",&n));
  printf("%d\n",fn(n));
  return 0;
}