prime check in c

1int isPrime(long long number) {
2
3	if (number == 0 || number == 1 || (number % 2 == 0 && number > 2)) {
4		return 0;
5	}
6
7	else {
8		for (long long i=3; i <= (long long)sqrt(number)+1; i++) {
9			if (number % i == 0) {
10				return 0;
11			}
12		}
13		return 1;
14	}
15}

1#include <stdio.h>
2int main() {
3    int n, i, flag = 0;
4    printf("Enter a positive integer: ");
5    scanf("%d", &n);
6
7    for (i = 2; i <= n / 2; ++i) {
8
9        // condition for non-prime
10        if (n % i == 0) {
11            flag = 1;
12            break;
13        }
14    }
15
16    if (n == 1) {
17        printf("1 is neither prime nor composite.");
18    }
19    else {
20        if (flag == 0)
21            printf("%d is a prime number.", n);
22        else
23            printf("%d is not a prime number.", n);
24    }
25
26    return 0;
27}
28