To check if it is prime number or not using c++

#include <iostream.h>

int smalldiv (int n) {
  int count; 
  count = 2;

  while (count < n && n % count != 0) {
    count = count + 1;
  }
  return(count);
}

int main () {
  int n;
  cout << "Enter a natural number: ";
  cin >> n;
  if (n == smalldiv(n)) {
    cout << n << " is a prime number" << endl;
  }
  else {
    cout << n << " is not a prime number" << endl;
  }
  return(0);
}