素数判定

//To determine a number is prime or not
int prime(int n)
{
    if(n==1) return -1;
    if(n==2) return 1;
    else if(n%2==0) return 0;
    else{
        for (int i=3;i<=sqrt(n);i+=2)
            if(n%i==0) return 0;
        return 1;
    }
}