Store and reuse intermediate variable

[oierpa]

Hi all.
One year ago I wrote a post related to subroutine, I'm here again becasue I had a turbulent year.
Some years ago I bought a HP 50g and I'm trying to program it with litte improvement ...

My problem is using local variable in a program, in detail store an intermediate value and reuse it.
To have practice I wrote a simple program that calculate mortgage installment (even if there are financial tools that alreade did it).
I would calculate the installment and the total amount paid (simply multiplying this intermediate value for number of years and months). My problem is store this value.
A sample of program is:

Code:


<<<<"Ins C t A " {
":C:
:t:
:A:" {1 0} V} INPUT OBJ-> -> C t A 
<<'C* (t/100/n)/(1-(1+t/100/n)^(-n*A))' -> R  ;I need to store this value in a local variale R and print on display
'R*A*12' ->NUM "M" ->TAG>> 
>>

Written in this way I can calcultate total amount (tagged with M) and result is correct, but intermediare R variable is not printed.

I red and checked tons of manuals but in didn't find some example that help me.
Thanks in advance.

[oierpa]

I make a variant of program, it use global variable ...

Code:


<<"Ins C t A " {
":C:
:t:
:A:" {1 0} V} INPUT OBJ-> -> C t A 
<<'C* (t/100/n)/(1-(1+t/100/n)^(-n*A))' -> NUM 'R' STO
'R*A*12' ->NUM 'M' STO
R "R" -> TAG
M "M" -> TAG>>
'R' PURGE
'M' PURGE 
>>

In this way I can obtain what I need, but in this way global variables are used, a practice not recommended by many.
How I can avoid use global variables?

[pinkman]

You should init R when initializing the other local vars, then you can simply ‘R’ STO and it will not create a global (HOME) var.

Example:

Code:


« "A" { 1 } INPUT OBJ-> 0 -> A B
 « 'A*2' ->NUM ‘B’ STO B 3 * »
»

[oierpa]

Hi Pinkman.
Thanks for answer.
I'm trying to avoid global variables as many people suggest.

Thanks

[pinkman]

(12-06-2022 07:13 AM)oierpa Wrote:  Hi Pinkman.
Thanks for answer.
I'm trying to avoid global variables as many people suggest.

Thanks

So do I. Did you try my suggestion?

[BruceH]

Hi Oierpa,

What Pinkman is suggesting is that you do this:

Code:

<<
  0 -> R   @ Dummy value to go into R which gets overwritten later
  <<
    "Ins C t A " {
    ":C:
     :t:
     :A:" {1 0} V} INPUT OBJ-> -> C t A 
    << 'C* (t/100/n)/(1-(1+t/100/n)^(-n*A))' ->NUM 'R' STO
        'R*A*12' ->NUM "M" ->TAG 
    >> 
  >>
>>

Note that during the INPUT, if the user recalls 'R' then they get the local zero value.

[pinkman]

Thank you BruceH!

Yes, once a local var is declared, you can update its value with the same syntax than with global vars.

Look at line 5: adding a 0 to be stored in local var R
Look at line 6: R is appended

Code:


« "Ins C t A " {
":C:
:t:
:A:" { 1 0
} V } INPUT OBJ→ 0
→ C t A R
  « 'C*(t/100/n)/(1
-(1+t/100/n)^(-n*A)
)' →NUM 'R' STO
'R*
A*12' →NUM "M" →TAG
  »
»

[oierpa]

Hi all.
Excuse me for delay, I was out for some days for my job.
I just tested program with your suggestions and it works!

Thanks a lot!
So in the future, if I have other variabiles (more than one) I've to inizialize with a dummy value, right?

I would to convert some program in RPL.

Thanks again!

[oierpa]

Hi all.
I just make a small variant to my simple program, in order to be general, here the code:

Code:


<<"Ins C t A n " {
":C:
:t:
:A:
:n:" {1 0} V} INPUT OBJ-> 0 -> C t A n R
<<'C* (t/100/n)/(1-(1+t/100/n)^(-n*A))' -> NUM 'R' STO R
>> 
>>

Now I can manage properly local variables, but with this code, where n (number of periods of mortgage) is a variable and not a fixed value.
In this version of program, I've the problem that, even if I wrote -> NUM, I can see an algebraic result (the formula) and not the results number.
I don't understood why, so after some tests I modified in this version;

Code:


<<"Ins C t A n " {
":C:
:t:
:A:
:n:" {1 0} V} INPUT OBJ-> 0 0 -> C t A n R P
<<'n*A' -> NUM 'P' STO P 'C* (t/100/n)/(1-(1+t/100/n)^(-P))' -> NUM 'R' STO R
>> 
>>

In this way, program is ok. In the stack, at the end, I can see number of period, morgage installment, and total debt.
Why if in the exponent I keep 'n*A' indeed P (=n*A) doesn't work?
Actually I don't need to display also "P" during calculation, in other programs, if I have to calculate intermediate values, is not important see the value on the stack.
Thanks in advance.

[Thomas Klemm]

You could also just duplicate the value with DUP before creating the local variable R:

Code:

« "Ins C t A n" {
":C:
:t:
:A:
:n:
" { 1 0 } V } INPUT OBJ→
→ C t A n
  « 'C*t/100/n/(1-(1+t/100/n)^(-n*A))'
    →NUM "R" →TAG DUP → R
    'R*A*12' →NUM "M" →TAG
  »
»

---

Just noted that you are now using → NUM instead of →NUM in your listing.
That could be the reason why you got an algebraic result.

[oierpa]

Thanks Thomas.
It was my error writing "-> NUM" indeed of "->NUM".
Thanks also for "DUP" suggestion.

Merry Christmas to everyone!