I wrote a simple C++ program in Visual Studio Community edition that checks if a number given to the program is a prime number or not:

#include <iostream>
using namespace std;

int main()
{   
    cout << "Please enter a number to find out if its a prime number: " << 'n';
    int number;
    cin >> number;

    int counter = 1;

    while (counter <= number / 2) 
    {
        if (number % counter == 0 && counter != 1 && counter != number)
        {
            cout << "The number is not a prime number." << 'n';
            cout << "The divisor is: " << counter;
            return 1;
        }
        else
        {
            if (counter == number / 2)
            {
                cout << "The number is a prime number.";
                return 0;
            }
        }

        counter++;
    }

}

The program works for small numbers but when it is given a big number, the program gives wrong answers. Where is the fault in the program?