### Finding if a number is prime

We need it to say if the number is prime or not we need the equation for the if statement or if we have something else wrong to let me know.

#include <iostream>
using namespace std;

int main ()

{
int number;
bool countr;

for (countr = 0; countr <= 2; countr ++)
{cout << " Enter a number to determine whether it is prime: " ;
cin >> number;
cout << endl;

if ()
{cout << number << " is prime " <<endl;
cout << endl;}
else
{cout << number << " is NOT prime " <<endl;
cout << endl;}

}

cin.ignore (10);
return 0;
}
http://www.cplusplus.com/forum/general/112468/

Are you ignoring my other reply?
Do the research!

Or if you're that lazy, here's a generous hint: a number is prime if the only numbers it divides exactly to (that means no remainder) are 1 and itself.

0 prime? no (divides with zero remainder to everything except itself and infinities)
1 prime? no (only divides to itself)
2 yes 1,2
3 yes 1,3
4 no, 1,2,4
5 yes 1,5
6 no 1,2,3,6
7 yes 1,7
8 no 1,2,4,8
9 no 1,3,9
10 no 1,2,5,10
11 yes 1,11
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