TI-82

This program produces a custimizable "HELLO WORLD" message, which will
flash until the batteries die out or you can guess the escape character
(optional).  
 
NOTE: Pressing the LEFT arrow key will shorten the message by 1 letter
(until there is no message), while pressing the RIGHT arrow key will add
one letter (until "HELLO WORLD" is fully displayed). 
 
PROGRAM HELOWRLD 
:11->A 
:Lbl A 
*:For (B, 1 ,  20 , 1) 
:getKey->C 
**:If C=74 
**:Stop 
:If C=26 
:Then 
:If A<=10 
:A+1->A 
:End 
:If C=24 
:Then 
:If A>=1 
:A-1->A 
:End 
:End 
:ClrHome 
:If A=1 
:Disp "H" 
:If A=2 
:Disp "HE" 
:If A=3 
:Disp "HEL" 
:If A=4 
:Disp "HELL" 
:If A=5 
:Disp "HELLO" 
:If A=6 
:Disp "HELLO " 
:If A=7 
:Disp "HELLO W" 
:If A=8 
:Disp "HELLO WO" 
:If A=9 
:Disp "HELLO WOR" 
:If A=10 
:Disp "HELLO WORL" 
:If A=11 
:Disp "HELLO WORLD" 
:Goto A 
 
*--Increase or decrease numbers for a different speed of blinking 
 
**--Optional 
 
-> is my equivalent of the results of pressing the STO> key.