factor.c

掌握如何用C来实现各种算法

/*****************************************************************************
*                                                                            *
*  ------------------------------- factor.c -------------------------------  *
*                                                                            *
*****************************************************************************/

#include <math.h>
#include <stdio.h>

#include "factor.h"

/*****************************************************************************
*                                                                            *
*  -------------------------------- factor --------------------------------  *
*                                                                            *
*****************************************************************************/

void factor(int number, int n, int j) {

int                i;

/*****************************************************************************
*                                                                            *
*  1 is neither prime nor composite.                                         *
*                                                                            *
*****************************************************************************/

if (n == 1) {

   printf("1 is a unit\n");
   return;

}

/*****************************************************************************
*                                                                            *
*  Determine the prime factors of n.                                         *
*                                                                            *
*****************************************************************************/

i = j;

while (i <= (int)(sqrt((double)n))) {

   if (n % i == 0) {

      /***********************************************************************
      *                                                                      *
      *  We have found a prime factor of n. Print it and factor n / i.       *
      *                                                                      *
      ***********************************************************************/

      fprintf(stdout, "%d\n", i);
      factor(number, (int)(n / i), i);
      return;

      }

   else {

      i++;

   }

}

/*****************************************************************************
*                                                                            *
*  If this point is reached, n is prime.                                     *
*                                                                            *
*****************************************************************************/

if (n == number)
   printf("%d is prime\n", number);
else
   printf("%d\n", n);

return;

}