It's pretty straight forward. The algorithm from wiki and this:
Code:
typedef unsigned int uint32_t; //(for the TEA)
str_cpy(plaintext,"Text to be encrypted");
str_cpy(key,"7813498");
returned = encrypt ((uint32_t)plaintext, (uint32_t)key);
wait(-5);
beep();
str_cpy (str_show, (STRING*)returned); //To show on screen
Then the same method for decrypting it back with the algorithm from the wiki. This example is the TEA, not XXTEA. I've also added return(v); at the end of the TEA function so "returned" catches it.