Prime number demonstrator

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>

/**
 * This is a simple program which will determine whether or not
 * a user has entered a prime number.
 *
 * @Shaun B
 * @1.0.0.1 - 2012-08-07
 */

int main();
static char run = 1;
static int readNumber = 0;

int main()
{
    system("cls");
    printf("Donkeysoft MMXII - this will determine whether or not\n");
    printf("the number you enter is a prime or even number. Please\n");
    printf("type in -1 to exit back to command line or 0 (zero) to\n");
    printf("clear the console window.\n\n");
    while (run)
    {
        printf("Please enter a whole (integer) number\n");
        printf("C:\\>");
        scanf("%d",&readNumber);
        if (readNumber%2 == 0)
        {
            printf("The integer that you entered is an even number\n");
        }
        else
        if ( (readNumber%2 != 0 && readNumber %3 != 0) || readNumber == 3)
        {
            printf("The integer that you entered is a prime number\n");
        }
        else
        {
            printf("The number is odd but not prime\n");
        }
        if (readNumber == 0 )
        {
            getchar();              // Clears keyboard buffer
            printf("\nPress any key to clear the screen.\n");
            getchar();              // Waits for keypress
            system("cls");
        }
        if (readNumber == -1 )
        {
            printf("\n\nGood bye, have a nice day :-)\n");
            run = 0;
        }
    }
    return 0;
}