/* * Calculate all primes up to a specific number. */#include <stdlib.h>#include <stdio.h>#include <ctype.h>#include <time.h>#include <conio.h>/*****************************************************************************//*     	      	    	  	     Data				     *//*****************************************************************************/#define COUNT		8192		/* Up to what number? */#define SQRT_COUNT	91		/* Sqrt of COUNT */static unsigned char Sieve[COUNT];/*****************************************************************************//*     	      	    	  	     Code     	      			     *//*****************************************************************************/#pragma staticlocals(1);int main (void){    /* Clock variable */    clock_t Ticks;    /* This is an example where register variables make sense */    register unsigned char* S;    register unsigned 	    I;    register unsigned 	    J;    /* Output a header */    printf ("Sieve benchmark - calculating primes\n");    printf ("between 2 and %u\n", COUNT);    printf ("Please wait patiently ...\n");    /* Read the clock */    Ticks = clock();    /* Execute the sieve */    I = 2;    while (I < SQRT_COUNT) {	if (Sieve[I] == 0) {	    /* Prime number - mark multiples */	    S = &Sieve[J = I*2];       	    while (J < COUNT) {	      	*S = 1;	      	S += I;	      	J += I;	    }	}	++I;    }    /* Calculate the time used */    Ticks = clock() - Ticks;    /* Print the time used */    printf ("Time used: %lu ticks\n", Ticks);    printf ("Press Q to quit, any other key for list\n");    /* Wait for a key and print the list if not 'Q' */    if (toupper (cgetc()) != 'Q') {     	/* Print the result */     	for (I = 2; I < COUNT; ++I) {     	    if (Sieve[I] == 0) {     		printf ("%4d\n", I);     	    }     	    if (kbhit() && toupper (cgetc()) == 'Q') {     		break;     	    }     	}    }    return EXIT_SUCCESS;}