Re: interest computing problem

Re: interest computing problem

[Robert I. Eachus]

 > That is definitely something that I need to look into.. making this 
program as you said a little more robust.

This is why it is such a good idea to 'echo back' the input data as your 
program sees it. There are all sorts of conversion and accuracy issues, 
plus the fact that your program can never tell if the way it interprets 
the numbers is the way that the user of the program intended.( I would 
avoid anthromorphizing the software here, except that makes it even more 
complicated to understand. The user may be a later edition of the 
author, as in this case. But from the program's point of view, the 
assumptions never changed...) If the percentage rate had been 'echoed' 
as 0.02% you would have seen the mistate immediately--or at least sooner.

interest computing problem

[Andrew]

ok I've run into a snag  .. and i'm hoping that a programmer can help me 
out.

here is a copy of my program (written in Ada)

====
-- computes Interest on money invested

with TEXT_IO;
use TEXT_IO;

procedure Interest is
    Initialamt : Float;
    Interest : Float;
    TimeNWeeks : Integer;
    DRate : Float;
    Days : Integer;
    Balance : Float;

    package NUMBER_IO is new INTEGER_IO(INTEGER);
    use NUMBER_IO;
    package Float1_IO is new Float_IO(FLOAT);
    use Float1_IO;

begin
    New_Line;
    Put ("How much money do you have-Please add cents? example 365.22 ");
    Get (Initialamt);

Put ("What is the interest you will receive? ");
    Get (Interest);
 

    Put ("How long will it be invested in weeks? ");
    Get (TimeNWeeks);
 

    New_Line;
 

    Days:=TimeNWeeks * 7;
    DRate:=(Interest/100.0)/365.0;
    Balance:=Initialamt * (1.0+DRate)**Days;
 

    New_Line;
    Put ("Your ending balance will be ");
    Put (Balance);
 

    New_Line;
end Interest;


========================================


now here is the output from when I try to run the program
==================
How much money do you have-Please add cents? .02
What is the interest you will receive? 25
How long will it be invested in weeks? 4


Your ending balance will be  2.03872E-02
[andrew@stc program]$ ./interest

How much money do you have-Please add cents? .02
What is the interest you will receive? .25
How long will it be invested in weeks? 4


Your ending balance will be  2.00038E-02

============

but I'm hoping that this is just a simple case of I .. well *L* I'm 
hoping this is a simple error that I'm overlooking..

sub-note : this program is directly copied from a printout of a program 
that I wrote in college (and it worked on the colleges computers).

By the way I'm writing this on a Red Hat Linux 9.0 computer (I don't 
think that would matter but ..)

Re: interest computing problem

[Ludovic Brenta]

Your program appears to be correct to me.  What were you expecting?

-- 
Ludovic Brenta.

Re: interest computing problem

[tmoran]

> > hoping this is a simple error that I'm overlooking..
> Your program appears to be correct to me.  What were you expecting?
  Perhaps he didn't realize that "What is the interest you will receive? "
is highly ambiguous and in the one case he entered 25, indicating 25%,
and in the other .25, which was interpreted as 1/4%.

Re: interest computing problem

[Andrew]

tmoran@acm.org wrote:
>>>hoping this is a simple error that I'm overlooking..
>>
>>Your program appears to be correct to me.  What were you expecting?
> 
>   Perhaps he didn't realize that "What is the interest you will receive? "
> is highly ambiguous and in the one case he entered 25, indicating 25%,
> and in the other .25, which was interpreted as 1/4%.

actually that a very ambiguous statement.. and regrettably I didn't 
properly document this program when I was in college.  but I do believe 
that the interest rate is to be entered in the not decimal format. i.e. 
25% is entered as 25

Re: interest computing problem

[Robert I. Eachus]

Andrew wrote:

>    New_Line;
>    Put ("Your ending balance will be ");
>    Put (Balance,1,2,0);

I think this will fix your problem, if I understand what you think is a 
problem.  If you want output in dollars and cents without exponents, 
this will do it. Look at the documentation for Put in 
Ada.Text_IO.Float_IO to understand why those numbers for the (otherwise 
defaulted) parameters.

-- 
                                         Robert I. Eachus

"As far as I'm concerned, war always means failure." -- Jacques Chirac, 
President of France
"As far as France is concerned, you're right." -- Rush Limbaugh

Re: interest computing problem

[Andrew]

Robert I. Eachus wrote:
> Andrew wrote:
> 
>>    New_Line;
>>    Put ("Your ending balance will be ");
>>    Put (Balance,1,2,0);
> 
> 
> I think this will fix your problem, if I understand what you think is a 
> problem.  If you want output in dollars and cents without exponents, 
> this will do it. Look at the documentation for Put in 
> Ada.Text_IO.Float_IO to understand why those numbers for the (otherwise 
> defaulted) parameters.
> 
OOOOH yeah.. that sounds very familiar.. I wrote the program initally in 
1997, and failed to properly document what things did and what they were 
for.

here is the output for the program as it is now
==============
How much money do you have-Please add cents? 1000.00
What is the interest you will receive? .02
How long will it be invested in weeks? 52

Your ending balance will be  1.00022E+03

============
and the ending balance should be 1020.2008 or more nicely written 1020.20
but I will try the change as you suggest.

.. .. .. ..

ok bit of a problem . now it says the output (or final balance is)
1000.22

that is not good.
and I had a friend who works at a local bank check the answer of 
1020.2008 and he says that, that is the correct answer.
any ideas?
thanks in advance.
Andrew

Re: interest computing problem

[Andrew]

Andrew wrote:
> 
> 
> Robert I. Eachus wrote:
> 
>> Andrew wrote:
>>
>>>    New_Line;
>>>    Put ("Your ending balance will be ");
>>>    Put (Balance,1,2,0);
>>
>>
>>
>> I think this will fix your problem, if I understand what you think is 
>> a problem.  If you want output in dollars and cents without exponents, 
>> this will do it. Look at the documentation for Put in 
>> Ada.Text_IO.Float_IO to understand why those numbers for the 
>> (otherwise defaulted) parameters.
>>
> OOOOH yeah.. that sounds very familiar.. I wrote the program initally in 
> 1997, and failed to properly document what things did and what they were 
> for.
> 
> here is the output for the program as it is now
> ==============
> How much money do you have-Please add cents? 1000.00
> What is the interest you will receive? .02
> How long will it be invested in weeks? 52
> 
> Your ending balance will be  1.00022E+03
> 
> ============
> and the ending balance should be 1020.2008 or more nicely written 1020.20
> but I will try the change as you suggest.
> 
> .. .. .. ..
> 
> ok bit of a problem . now it says the output (or final balance is)
> 1000.22
> 
> that is not good.
> and I had a friend who works at a local bank check the answer of 
> 1020.2008 and he says that, that is the correct answer.
> any ideas?
> thanks in advance.
> Andrew
> 


I felt that I should add a note here, so that there is no confusion.
when I said "ok bit of a problem . now ....." what I meant was that I 
had made the programming change that you suggested and wound up with the 
  value of 1000.22, the value of 1.00022E+03 was achieved before making 
the programming adjustment.

Re: interest computing problem

[tmoran]

>Your ending balance will be  1.00022E+03
  If you use Long_Float instead of Float you will get
1.02014488268319E+03
Raising to the 365th, rather than 364th (7*52=364) power gives
1.02020078103290
which matches within rounding error what your banker friend says.

Re: interest computing problem

[Andrew]

tmoran@acm.org wrote:
>>Your ending balance will be  1.00022E+03
> 
>   If you use Long_Float instead of Float you will get
> 1.02014488268319E+03
> Raising to the 365th, rather than 364th (7*52=364) power gives
> 1.02020078103290
> which matches within rounding error what your banker friend says.
i just tried to use long_float

although I am probably mis-using it

here is my attempted implementation of it .. sorry about the spelling 
it's now 2:42 am

=========
procedure Interest is
    Initialamt : Long_Float;
    Interest : Long_Float;
    TimeNWeeks : Integer;
    DRate : Long_Float;
    Days : Integer;
    Balance : Long_Float;
 

    package NUMBER_IO is new INTEGER_IO(INTEGER);
    use NUMBER_IO;
    package Float1_IO is new Float_IO(FLOAT);
    use Float1_IO;
 

===========

do I need to also make
package Float1_IO is new Float_IO(FLOAT);
be
package Float1_IO is new Float_IO(Long_FLOAT);

actually I'll try that...

nope that didn't help either....

i'm probably not using "Long_Float" correctly...

if you want could you show me the correct syntax..

either that or else I'll try to look it up in the morning.. i need some 
slpee.. err sleep

Re: interest computing problem

[Andrew]

Andrew wrote:
> 
> 
> tmoran@acm.org wrote:
> 
>>> Your ending balance will be  1.00022E+03
>>
>>
>>   If you use Long_Float instead of Float you will get
>> 1.02014488268319E+03
>> Raising to the 365th, rather than 364th (7*52=364) power gives
>> 1.02020078103290
>> which matches within rounding error what your banker friend says.
> 
> <<<<Snip>>>><<<<Snip>>>>


ok after a few hours of sleep.. I got Long_Float to work(aka the program 
compiled), but the input/output that I got is still

How much money do you have-Please add cents? 1000.00
What is the interest you will receive? .02
How long will it be invested in weeks? 52


Your ending balance will be 1000.20


as you can see it now says that the ending balance is 1000.20 which is 
changed from 1000.22 (and the can probably be attributed to the fact 
that I am using Long_Float instead of Float).  but I am still at the 
problem of the answer should be 1020.20 (or the full answer that he came 
up with 1020.2008).  he did acknowledge the fact that I am really only 
computing for 364 days instead of 365 but none the less, I am loosing 
the equivalent of 20 dollars in the program.  If i was loosing 15 cents 
or some minor amount I would accept that was just because of the loss of 
the day, but 20?  *L* thankfully this isn't a real bank computer program 
or I'd have a lot of pissed off customers.

I think I'm going to ask 2 important question:
based upon the coding which I have pasted at the bottom of the page..
1: is the interest being compounded on a daily basis? (which I believe 
it is and my friend also believes the same.)

2.  is the line of
Balance:=Initialamt * (1.0+DRate)**Days;
really saying.. take the value in DRate and add 1.0 to it and take that 
to the power of the value in Days.
ex:
DRate = 4
Days = 5
Initalamt = 100.00
would really be taken as
100.00 * (1.0 + 4)^5
because if I remember correctly the ** just means 'to the power of'

here is the current coding
======================

with TEXT_IO;
use TEXT_IO;
 

procedure Interest is
    Initialamt : Long_Float;
    Interest : Long_Float;
    TimeNWeeks : Integer;
    DRate : Long_Float;
    Days : Integer;
    Balance : Long_Float;
 

    package NUMBER_IO is new INTEGER_IO(INTEGER);
    use NUMBER_IO;
    package Float1_IO is new Float_IO(Long_FLOAT);
    use Float1_IO;
 

begin
    New_Line;
    Put ("How much money do you have-Please add cents? ");
    Get (Initialamt);

    Put ("What is the interest you will receive? ");
    Get (Interest);
 

    Put ("How long will it be invested in weeks? ");
    Get (TimeNWeeks);
 

    New_Line;
 

    Days:=TimeNWeeks * 7;
    DRate:=(Interest/100.0)/365.0;
    Balance:=Initialamt * (1.0+DRate)**Days;
 

    New_Line;
    Put ("Your ending balance will be ");
    Put (Balance,1,2,0);
 

    New_Line;
end Interest;
=========================================

and here is the bottom line question:
any ideas of where I am loosing the 20 dollars at?
needed answer - current answer = 20
1020.20 - 1000.20 = 20
?

please help
Andrew

Re: interest computing problem

[Martin Dowie]

"Andrew" <eagletalon@chartermi.net> wrote in message
news:vmh1jlmbuvrb8f@corp.supernews.com...
> ok after a few hours of sleep.. I got Long_Float to work(aka the program
> compiled), but the input/output that I got is still
>
> How much money do you have-Please add cents? 1000.00
> What is the interest you will receive? .02
> How long will it be invested in weeks? 52
>
>
> Your ending balance will be 1000.20
>
>
> as you can see it now says that the ending balance is 1000.20 which is
> changed from 1000.22 (and the can probably be attributed to the fact
> that I am using Long_Float instead of Float).  but I am still at the
> problem of the answer should be 1020.20 (or the full answer that he came

You input ".02" which you are then dividing by 100 to get a percentage, so
your "bank" is paying 0.0002% - I'd say 20cents is about right at that rate!

Try your same program but enter "2.0" (miss quotation marks) for the
second value and you will get the result "1020.14" - which is a lot
closer...

Re: interest computing problem

[Leon Winslow]

Andrew

Your program is a good example of a student homework program.  It works, as
long as you remember all of the assumptions you made in writing it.  This is
about as much as most instructors expect of their students and I'm sure you
got a good grade on it.

It might be instructive, however, to rewrite it in a more robust version.
For example, define some data types and check the input for valid values.
Thus, real money is always integers (minimum value is one cent, not .00001 or
some such) and interest is either an integer type 3% or a float type .12%
depending on what you want.  Note this will require you to define exactly how
one computes interest times dollars.  All of these details are one reason
real programs tend to look long and complicated to outsiders.

If you can do a robust version of this problem, you will have accomplished
something past what your instructor expected.

Its always good to see another new Ada programmer.  Good luck in your
endeavors.

Lee Winslow

Andrew wrote:

> ok I've run into a snag  .. and i'm hoping that a programmer can help me
> out.
>
> here is a copy of my program (written in Ada)
>
> ====
> -- computes Interest on money invested
>
> with TEXT_IO;
> use TEXT_IO;
>
> procedure Interest is
>     Initialamt : Float;
>     Interest : Float;
>     TimeNWeeks : Integer;
>     DRate : Float;
>     Days : Integer;
>     Balance : Float;
>
>     package NUMBER_IO is new INTEGER_IO(INTEGER);
>     use NUMBER_IO;
>     package Float1_IO is new Float_IO(FLOAT);
>     use Float1_IO;
>
> begin
>     New_Line;
>     Put ("How much money do you have-Please add cents? example 365.22 ");
>     Get (Initialamt);
>
> Put ("What is the interest you will receive? ");
>     Get (Interest);
>
>
>     Put ("How long will it be invested in weeks? ");
>     Get (TimeNWeeks);
>
>
>     New_Line;
>
>
>     Days:=TimeNWeeks * 7;
>     DRate:=(Interest/100.0)/365.0;
>     Balance:=Initialamt * (1.0+DRate)**Days;
>
>
>     New_Line;
>     Put ("Your ending balance will be ");
>     Put (Balance);
>
>
>     New_Line;
> end Interest;
>
> ========================================
>
> now here is the output from when I try to run the program
> ==================
> How much money do you have-Please add cents? .02
> What is the interest you will receive? 25
> How long will it be invested in weeks? 4
>
> Your ending balance will be  2.03872E-02
> [andrew@stc program]$ ./interest
>
> How much money do you have-Please add cents? .02
> What is the interest you will receive? .25
> How long will it be invested in weeks? 4
>
> Your ending balance will be  2.00038E-02
>
> ============
>
> but I'm hoping that this is just a simple case of I .. well *L* I'm
> hoping this is a simple error that I'm overlooking..
>
> sub-note : this program is directly copied from a printout of a program
> that I wrote in college (and it worked on the colleges computers).
>
> By the way I'm writing this on a Red Hat Linux 9.0 computer (I don't
> think that would matter but ..)

Re: interest computing problem

[Andrew]

Leon Winslow wrote:
> Andrew
> 
> Your program is a good example of a student homework program.  It works, as
> long as you remember all of the assumptions you made in writing it.  This is
> about as much as most instructors expect of their students and I'm sure you
> got a good grade on it.
> 
> It might be instructive, however, to rewrite it in a more robust version.
> For example, define some data types and check the input for valid values.
> Thus, real money is always integers (minimum value is one cent, not .00001 or
> some such) and interest is either an integer type 3% or a float type .12%
> depending on what you want.  Note this will require you to define exactly how
> one computes interest times dollars.  All of these details are one reason
> real programs tend to look long and complicated to outsiders.
> 
> If you can do a robust version of this problem, you will have accomplished
> something past what your instructor expected.
> 
> Its always good to see another new Ada programmer.  Good luck in your
> endeavors.
> 
> Lee Winslow
> 
> Andrew wrote:
> 
> 
>>ok I've run into a snag  .. and i'm hoping that a programmer can help me
>>out.
>>
>>here is a copy of my program (written in Ada)
>><<<Snip>>><<<Snip>>>
>>============
>>
>>but I'm hoping that this is just a simple case of I .. well *L* I'm
>>hoping this is a simple error that I'm overlooking..
>>
>>sub-note : this program is directly copied from a printout of a program
>>that I wrote in college (and it worked on the colleges computers).
>>
>>By the way I'm writing this on a Red Hat Linux 9.0 computer (I don't
>>think that would matter but ..)
> 
> 



That is definitely something that I need to look into.. making this 
program as you said a little more robust.

and thank you for the good luck.
Andrew