/* Determines whether entry is a prime number, if not, gives factors. Enter "1" to quit. */
/* By mattt chisholm - September 2, 1996 */
/* September 29, 1996: Made it stop checking for factors after it reaches halfway */
#include <stdio.h>
#include <math.h>

main()
{
        int pa;                 /* integer to test */
        int pb = 0;             /* possible integer factors */
        double pg;              /* half the integer to test, decimal */
        int ph;                 /* half the integer to test plus 1 for good measure, integer */
        double pc;              /* a, in decimal form */
        double pd;              /* b, in decimal form */
        double pe;              /* c divided by d */
        double pf;              /* next greatest integer to e*/
        int pz;                 /* off switch: checks for a being 1 */
        int px;                 /* not a prime switch */

        pz = 0;

        while ( pz < 1 ){               /* when z is 1, it means quit */

                if (pb > 0) {
                        printf("\nThat took %d steps", pb);
                        }

                pb = 2;                 /* start with 2 because everything is divisible by 1 */

                printf("\n\nEnter number, 1 to quit > ");
                scanf("%d", &pa);       /* get number to test */

                px = 0;                 /* we don't know if it is a prime yet */

                if ( pa == 1) {         /* did the user enter a 1 to quit ? */
                        pz = 1;
                        }

                pg = (pa)/(2);          /* factor is never going to be more than half of multiple */
                ph = ceil(pg) + 1;      /* add one for good measure (without, thinks 4 is prime) */

                while ( pb < ph ) {     /* start dividing by numbers less than test number */
                        pc = pa;        /* set the integer a to the decimal c */
                        pd = pb;        /* set the integer b to the decimal d */
                        pe = (pc) / (pd);       /* divide */
                        pf = ceil(pe);          /* get the closest integer to e*/

                        if ( pf == pe ) {       /* if the closest integer is the same, it divides evenly, and is not a prime */
                                printf("\n%d is divisible by %d.", pa, pb); /* tell us about it */
                                px = 1;         /* remember, this is not a prime */
                                }
                        pb = pb + 1;            /* move on to the next number to divide a by */
                        }


                if ( px == 0) {                 /* was this ever designated "not a prime?" */
                                printf("\n%d is a prime.", pa); /* tell us about it */

                }


        }

        printf("\nthat took %d steps", pb);
        printf(" Either that, or it isn't a prime. Thank you for usingPrimeFinder.\n");
        return(0);

}