\C
factor.c
```/*
** factor.c -- print prime factorization of a number
** Ray Gardner -- 1985 -- public domain
** Modified Feb. 1989 by Thad Smith > public domain
**
** This version takes numbers up to the limits of double precision.
*/

#include
#include
#include

int prevfact = 0;
void factor (double);
void show (double, int);

void main (int argc, char *argv[])
{
while ( --argc )
factor(atof(*++argv));
}

void factor (double n)
{
double d;
int k;

prevfact = 0;

d = n+1;     /* test for roundoff error */
if (n+3 != d+2)
{
printf("%0.0f is too large to process.\n", n);
return;
}
if (fmod(n,1.) != 0.0)
{
printf("%f is not an integer.\n",n);
return;
}
printf("%0.0f  ",n);
if ( n < 2. )
{
printf("is less than 2.\n");
return;
}
else if ( n > 2. )
{
d = 2;
for ( k = 0; fmod(n,d) == 0.0; k++ )
n /= d;
if ( k )
show(d,k);
for ( d = 3; d * d <= n; d += 2 )
{
for ( k = 0; fmod(n,d) == 0.0; k++ )
n /= d;
if ( k )
show(d,k);
}
}
if ( n > 1 )
{
if ( ! prevfact )
printf(" is prime");
else  show(n,1);
}
printf("\n");
}

void show (double d, int k)
{
if ( prevfact )
printf(" * ");
else  printf(" = ");
prevfact++;
printf("%0.0f",d);
if ( k > 1 )
printf("^%d",k);
}
```