/********************************************
*              PRIME NUMBERS                *
* ----------------------------------------- *
* This small program tests if a given inte- *
* ger number is a prime number or not.      *
* ----------------------------------------- *
* Ref.: "Mathématiques par l'informatique   *
*        individuelle (1) par H. Lehning    *
*        et D. Jakubowicz, Masson, Paris,   *
*        1982" [BIBLI 06].                  *
*                                           *
*              C++ version by J-P Moreau.   *
*                  (www.jpmoreau.fr)        *
********************************************/
//See also program factors.cpp
#include <stdio.h>
#include <math.h>

//Labels: e100, fin

double d,eps,i,m,n;

void main() {
  eps=1e-6;
  printf("\n");
  printf(" ? "); scanf("%lf",&n);
  printf("\n");
  //Test if multiple of 2
  d=n-2*int(n/2);
  if (fabs(d)<eps) goto e100;
  //Test if multiple of 3
  d=n-3*int(n/3);
  if (fabs(d)<eps) goto e100;
  //Test if multiple of 6i-1 and 6i+1 from i=6 to sqrt(N)+1
  i=6; m=floor(sqrt(n))+1;
  while (i<=m)  {
    d=n-(i-1)*int(n/(i-1));
    if (fabs(d)<eps) goto e100;
    d=n-(i+1)*int(n/(i+1));
    if (fabs(d)<eps) goto e100;
    i=i+6;
  }
  printf(" Prime number.\n"); goto fin;
e100:printf(" Not a prime number.\n");
fin:printf("\n");
}

// end of file prime.cpp