prime number

#include <stdio.h>
int main()
{
    int n, i, a = 1;

    printf("Enter a number: ");
    scanf("%d", &n);

    if (n==1){
        printf("%d is neither prime nor composite", n);
    }
    else{
        for (i = 2; i <= sqrt(n); i++) {
            if (n % i == 0) {
                a = 0;
                break;
            }
        }

        if (n <= 1)
            a = 0;

        if (a == 1) {
            printf("%d is a prime number", n);
        }
        else {
            printf("%d is not a prime number", n);
        }
    }
    return 0;
}