primes

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

//prints list of primes of given length

//Uses Sieve of Erastothenes, modified from:
//http://stackoverflow.com/a/19088/203705

int main(int argc, char** argv)
{
    unsigned int lim, i, j, len, start;

    if(argc != 2){
        printf("Usage: %s length\n", *argv);
        return 0;
    }

    sscanf(*(argv+1), "%d", &len);

    //for len=2, start=10, lim=100
    start = (unsigned int)pow(10.0, (double)(len-1));
    lim = (unsigned int)pow(10.0, (double)(len));

    bool *primes = calloc(lim, sizeof(bool));

    unsigned int sqrtlim = sqrt(lim);
    for (i = 2; i <= sqrtlim; i++)
        if (!primes[i])
            for (j = i * i; j < lim; j += i)
                primes[j] = true;

    for (i = start; i < lim; i++)
        if (!primes[i])
            printf("%d\n", i);

    free(primes);

    return 0;
}