sol2.c File Reference

Problem 10 solution More...

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

Include dependency graph for sol2.c:

Functions
int	main (int argc, char *argv[])
	Main function. More...

Detailed Description

Problem 10 solution

Author

Krishna Vedala

Function Documentation

main()

int main	(	int	argc,
		char *	argv[]
	)

Main function.

{
    long n = 100;
    long long sum = 0;
    char *sieve = NULL;
 
    if (argc == 2)         /* if command line argument is provided */
        n = atol(argv[1]); /* use that as the upper limit */
 
    /* allocate memory for the sieve */
    sieve = calloc(n, sizeof(*sieve));
    if (!sieve)
    {
        perror("Unable to allocate memory!");
        return -1;
    }
 
    /* build sieve of Eratosthenes
        In the array,
        * if i^th cell is '1', then 'i' is composite
        * if i^th cell is '0', then 'i' is prime
    */
    for (long i = 2; i < sqrtl(n); i++)
    {
        /* if i^th element is prime, mark all its multiples
        as composites */
        if (!sieve[i])
        {
            for (long j = i * i; j < n + 1; j += i)
            {
                sieve[j] = 1;
            }
            sum += i;
        }
    }
 
    for (long i = sqrtl(n) + 1; i < n; i++)
        if (!sieve[i])
            sum += i;
 
    free(sieve);
 
    printf("%ld: %lld\n", n, sum);
 
    return 0;
}