New user, really need some help writing my first loop

Your loop runs endlessly because:

It only stops when Apercent >= 100. So how does Apercent change during the loop...?

Just before the last statement in the While block, you assign Arep/Ar to Apercent. Within the while block you do NOT assign new values to Arep or Ar, which means that Apercent gets assigned the same value over and over again, and (apparently) that value is not over 100...Well, you do assign to Arep, namely A1+A2A3+A3a, but those values don't change in the program.

Some other remarks:

- Francesco is right, you shouldn't name the function the same as its internal variable. I renamed it to Result.

- if( <condition> , <action if true> , <action if false> ) is a function, like sin() and mean(), that you can just use as is. You don't need to precede it with a programming bar. I took all these items out. {That is different for an 'if' statement that you find on the programming tab, but you've not used that. (I'm as limited with Prime as Fred, for me Prime Express only, so I can't program it for you).}

- You can have evaluation with every definition such as when you define Lv := L - M, you follow it by an equals '=' to display the resulting value. What you should know that this sometimes results in unexpected behaviour of the sheet. I would advise against it. You did the same when you defined the program, now called Result(). You immediately evaluate it (by having that = follow it).  - don't - (That's why I took it off)

- In your program you assign a value to dttr, but it's used nowwhere in the program. So why assign it?

I think there's room for improvement, your turn again.

(Your worksheet opened in Prime 4, I'm assuming you're using Prime 4, otherwise you can't open my sheet.)

Success!
Luc