[Dev-C++] non-lvalue error?

[Heedle B. <hee...@gm...>]

Here is my code:

#include <iostream>

using namespace std;
int main ()
{
    int n;
    int div = 0;
    bool primenum = true;
    cout << "Enter an integer: ";
    cin >> n;
    do {
        div = div + 1;
        if (n % div = 0)
        {
              cout << "Divisible By " << div << " ." << endl;
              primenum = false;
        }
        if (n % div != 0)
        {
              cout << "Not Divisible By" << div << " ." << endl;
        }
        } while (div <= n / 2 + 1); */* this line has the error*/*
    if (primenum == false)
    {
              cout << "IS PRIME." << endl;
    }
    if (primenum == true)
    {
              cout << "IS NOT PRIME." << endl;
    }
    system("pause > nul");
    return (0);
}

And here is my question:

I recieve a non-lvalue error in the line with "this line has the error".

What the heck is a non-lvalue error and how do I fix it?

My system specs (though I don't think they'll matter) :

Microsoft Windows XP
Service Pack 3

Intel Pentium 4
504 MB RAM
3.06 GHZ of processing


Thank you so much.

Heedle

P.S. Please don't disregard my questions because there are so many of them.
I say again, I am new to C++.