30-second algorithm to check if a number is prime

main.c

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

int isPrime(int x) {
    if (x < 2 || x % 2 == 0 && x != 2) {
        return 0;
    }
    
    int d;
    int s = floor(sqrt(x));
    for (d = 3; d <= s; d += 2) {
        if (x % d == 0) {
            return 0;
        }
    }
    return 1;
}

int main(int argc, char* argv[]) {
    if (isPrime(17) == 1) {
        printf("Is prime\n");
    } else {
        printf("Is not prime\n");
    }
    return 0;
}