problem35.c

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

const int sizes[] = { 9, 99, 999, 9999, 99999, 999999, 9999999 };

int get_places(int number) {
    for (int i = 0; i < 6; i++) {
        if (number <= sizes[i]) {
            return i + 1;
        }
    }

    return -1;
}

bool is_prime(int number) {
    if (number % 2 == 0) {
        return false;
    }

    for (int i = 3; i < ((int) sqrt(number)) + 1; i += 2) {
        if (number % i == 0) {
            return false;
        }
    }

    return true;
}

bool is_circ_prime(int number) {
    if (!is_prime(number)) {
        return false;
    }

    /*int places = log10(number) + 1;*/
    int places = get_places(number);

    for (int i = 0; i < places; i++) {
        if (i > 0 && !is_prime(number)) {
            return false;
        }

        number = (number / 10) + ((number % 10) * pow(10, places - 1));
    }

    return true;
}

int main(int argc, char** args) {
    int count = 1;

    for (int i = 3; i < 1000000; i += 2) {
        if (is_circ_prime(i)) {
            count++;
        }
    }

    printf("%d\n", count);

    return 1;
}