54 lines
857 B
C
54 lines
857 B
C
/* factor - print the prime factors of a number Author: Andy Tanenbaum */
|
|
|
|
#include <stdlib.h>
|
|
#include <stdio.h>
|
|
|
|
int main(int argc, char **argv);
|
|
long first(long k);
|
|
|
|
int main(argc, argv)
|
|
int argc;
|
|
char *argv[];
|
|
{
|
|
/* Factor a number */
|
|
|
|
long i, n, flag = 0;
|
|
|
|
if (argc != 2 || (n = atol(argv[1])) < 2) {
|
|
printf("Usage: factor n (2 <= n < 2**31)\n");
|
|
exit(1);
|
|
}
|
|
if (n == 2) {
|
|
printf("2 is a prime\n");
|
|
exit(0);
|
|
}
|
|
while (1) {
|
|
i = first(n);
|
|
if (i == 0) {
|
|
if (flag == 0)
|
|
printf("%ld is a prime\n", n);
|
|
else
|
|
printf("%ld\n", n);
|
|
exit(0);
|
|
}
|
|
printf("%ld ", i);
|
|
n = n / i;
|
|
flag = 1;
|
|
}
|
|
}
|
|
|
|
|
|
long first(k)
|
|
long k;
|
|
{
|
|
/* Return the first factor of k. If it is a prime, return 0; */
|
|
|
|
long i;
|
|
|
|
if (k == 2) return(0);
|
|
if (k % 2 == 0) return (2);
|
|
for (i = 3; i <= k / 3; i += 2)
|
|
if (k % i == 0) return(i);
|
|
return(0);
|
|
}
|