xBee API Mode Sending Data with Frames

I’m trying to make a frame that sends a specified message.
I’m following this article: http://knowledge.digi.com/articles/Knowledge_Base_Article/Calculating-the-Checksum-of-an-API-Packet
So in order to send a message, there must be some calculations and frame must obey the rules otherwise xBee can’t send the message.
Making the LENGTH BYTES is easy. sizeof() function can do it. But i stuck on making CHECKSUM.
My code is following:

byte START_DELIMITER = 0x7E; // Don't change
byte LENGTH_BYTES_1 = 0x00; // Don't change
byte LENGTH_BYTES_0 = 0x00; // Will be changed
byte API_IDENTIFIER = 0x01; // Don't change
byte API_FRAME_ID = 0x01; // Don't change
byte DESTINATION_LOW_1 = 0xFF; // Don't change
byte DESTINATION_LOW_0 = 0xFF; // Don't change
byte OPTION_BYTE = 0x00; // Don't change
byte CHECKSUM = 0x00; // Will be changed

char message[] = "NODE01"; // message

void setup() 

void loop() 
  LENGTH_BYTES_0 = (byte)(sizeof(message));


Code is not working.
How can i achieve to the CHECKSUM in the link?
Then i can continue to create to my frame.
Best regards.

The checksum is computed from the bytes in the message, not the address of the message.