Keygen for a certain program

Keygen.c

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

int main(int argc, char** argv) {

	//Todo: extract registry value automatically, more validation
	
	//Date lives here:
	//HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System\SystemBiosDate
	char user_date[9] = "08/25/11"; //Example date
	
	int date_firsthalf = 0;
	int date_secondhalf = 0;
	int key = 0;

	printf("Enter date: ");
	scanf("%s", user_date);
	
	if (strlen(user_date) == 8) {

		date_firsthalf = *(int*)user_date;
		date_secondhalf = *(int*)(user_date + 4);
		
		key = date_firsthalf + date_secondhalf;
		key ^= date_secondhalf;
		key ^= 314159265;
		key = abs(key);

		printf("Magic= %i \n", key);
		
	} else {
		printf("Invalid Date\n");
	}

	return 0;
}