Complexity of a code?

Question

optimisation of a function

Answer 1

Can anyone do and explain this?

Below is a function that determines whether the number is prime. The complexity of the code is O (n). Optimize the code so that its complexity is O (n½).

bool isPrime (int n)
{ if (n <= 1)
return false;
for (int i = 2; i <n; i ++)
if (n% i == 0)
return false;
return true; }

Answer 2

in order to find if a number is prime or not, u just need to divide it until half of its number(cause above half wont divide evenly no matter what)
eg: 12 : divide from 2 to 6, 13 : divide from 2 to 6

Answer 3

I understand. So,

It looks then like this:

bool isPrime(int n)
{
    if (n <= 1)
        return false;

    for (int i = 2; i < (n/2); i++)
        if (n % i == 0)
            return false;

    return true;
}

And this code have complexity 0( n ^1/2)?