How quickly determine prime numbers

Ideas:

1. The number of square root
2. Query result is traversed square root itself and in addition there is a factor, if any, is not a prime number, if not, a prime number

Code:

bool isPrime(int n){//判断是否素数
    int s=sqrt(double(n));//开根
    for(int i=2;i<=s;i++)
    {//查找因子
        if(n%i==0)
        	return false;
    }
    return true;
}