\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); }