/*********************************************************
 * From C PROGRAMMING: A MODERN APPROACH, Second Edition *
 * By K. N. King                                         *
 * Copyright (c) 2008, 1996 W. W. Norton & Company, Inc. *
 * All rights reserved.                                  *
 * This program may be freely distributed for class use, *
 * provided that this copyright notice is retained.      *
 *********************************************************/

/* prime.c (Chapter 9, page 190) */
/* Tests whether a number is prime */

#include <stdio.h>

/* Using hard coded numbers in a C progam is a bad practice that should be
   avoided. Here, we demonstrate that instead of using numebrs 1 and 0,
   define readable abbreviations. They are much easier to revise, if needed.
*/
#define TRUE  1
#define FALSE 0

int is_prime(int n)
{
  int divisor;
/* This example demonstrates that the body of a function may have more than one
   return statement. But when this function is called, only one return statement
   can ever be executed. 
*/
  if (n <= 1)
  	return FALSE;
  	
  for (divisor = 2; divisor * divisor <= n; divisor++)
  	if (n % divisor == 0)
  		{ printf("The number %d has divisor %d\n",n,divisor);
  		  return FALSE;
  		 }
  return TRUE;
}


int main(void)
{
  int n;

  printf("Enter a number: ");
  scanf("%d", &n);
  
  /* Notice that main contains a variable named n even though is_prime's
     argument is also named n. This is OK since the name of a parameter or a
     local variable in one function can be freely reused in any other function.
  */   
  if (is_prime(n))
  	printf("Prime\n");
  else
  	printf("Not prime\n");

  return 0;
}