To C programmers

alfcen · #1 (**permalink**) 10-15-2011, 07:28 AM

Hi,
Trying to convert a routine in C to B4A and get false results, believing that the code marked in red is wrongly converted. Anyone who could fix that for me?
Thanks a lot!
Robert

Code:

int get_new_uranometria_page( const double ra, const double de)
{
   int zone = (int)( (90. - de) * 16. / 180. + .5);
   const char zone_splits[17] = { 1, 6, 10, 12, 15, 18, 18, 20, 20,
               20, 18, 18, 15, 12, 10, 6, 1 };
   int rval = (int)( (24. - ra) * (double)zone_splits[zone] / 24. + .5);
   rval %= zone_splits[zone];
   while( zone--)
      rval += zone_splits[zone];
   return( rval + 1);
}

Code:

Sub PageNewUranometria(ra As Double, de As Double) As Int
    Dim zone, rval As Int
    Dim zone_splits() As Int
    zone = Floor(90 - de) * 16 / 180 + 0.5
    zone_splits = Array As Int(1, 6, 10, 12, 15, 18, 18, 20, 20, 20, 18, 18, 15, 12, 10, 6, 1)
    rval = ((24 - ra) * zone_splits(zone) / 24 + .5)
    rval = rval Mod zone_splits(zone)
<font color="Red">    Do While rval = rval - 1
        zone = zone - 1
        rval = rval + zone_splits(zone)
    Loop</font>
    Return rval + 1
End Sub

derez · #2 (**permalink**) 10-15-2011, 07:53 AM

I'm not sure what should happen in the line

Code:

while( zone--)

I guess it check the value of zone after reducing it , I don't know when it is true and when false (positive ?)
In your translation you test

Code:

Do While rval = rval - 1

and it will never be true so the loop will not run.

alfcen · #3 (**permalink**) 10-15-2011, 07:59 AM

Quote:

I'm not sure what should happen in the line
while( zone--)

That's exactly what I do not understand either.
Anyway, thanks for writing, Derez

thedesolatesoul · #4 (**permalink**) 10-15-2011, 10:43 AM

Quote:

Originally Posted by alfcen

That's exactly what I do not understand either.
Anyway, thanks for writing, Derez

That is a post-decrement.
The zone-1 statement will be executed AFTER the while check.
If you want it to happen before then make it: --zone

EDIT:
I think this should be:

Code:

Do While (zone > 0)
        zone = zone - 1
        rval = rval + zone_splits(zone)
    Loop

alfcen · #5 (**permalink**) 10-15-2011, 10:58 AM

Hi thedesolatesoul,

Quote:

Do While (zone > 0)

Bingo! That was the key. The results are poin-point.
Thanks so much for your expert help.

Cheers
Robert

thedesolatesoul · #6 (**permalink**) 10-15-2011, 12:04 PM

Im no expert

Glad it is solved!

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