Using C++ in .net and the sqrt()

I am trying to create a program that will decipher whether a number is prime or composite. I am hitting a few roadblocks. First of all .net will not allow me to use the sqrt() command, but yet when I put in the same exact code into Visual Studio 6.0 it allows me to do so, what command can I use in .net to allow me to create this program.

This is what I have so far (mind all of you, I am a college student just getting into the C++ programming field, I have basic and java knowlegde, so I am not totally oblivious)

#include <iostream>
#include <cmath>

using namespace std;

int main()
{

int i = 2;
int x;

cout << "Enter an interger and this program will tell whether it is prime or composite. " << endl;
cin >> x;

while (i <= sqrt(x))
cout <<




system("PAUSE")
return 0

}


Now the professor is saying that we have to use the sqrt() command for this program, I have figured out how to create a program that will decipher prime by using for loops with an if/else inside the for loop.

Any help would be GREATLY APPRECIATE and thanks in advance,
Chris

Oh and FYI i cannot even put the following code into C++

cout << sqrt(9) << endl;

even that will not work