HP 40gs HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 291

The Graphics commands See the chapter "Programming the hp 39gs & hp 40gs" beginning on page 255 for examples illustrating some of the graphics commands that I have used regularly. Consult the manual for more. The Loop commands FOR = TO [STEP ] END For those familiar with the Basic language in other forms, this is a standard FOR...NEXT command, except without the 'NEXT'. The STEP value is optional and is assumed to be 1 if not stated. Note: Whatever you do, don't use NEXT to terminate the loop! It doesn't register as an error but all sort of strange things happen! DO UNTIL END This loop executes the statements within it until the test clause evaluates as true. It must execute at least once because the test is not done until the end of the loop. The example right checks for a positive integer from the INPUT statement. To be even more user friendly you could let the user know what they had done wrong by adding another few lines of code within the DO loop of.. IF INT(N) N OR N 0 THEN MSGBOX "Enter a positive integer only": END: WHILE REPEAT END This is similar to the DO...UNTIL loop except that the test clause is evaluated before starting so that the loop may not be executed at all. These two loops are very similar and, except in some odd situations, are interchangeable. 291