Issue with RoundTO

[Bazzao]

Issue with RoundTO

All I get is a 0 or a 1. Is there a bug?:

Code: Pascal  [Select][+][-]

1. procedure MakeRoundTos;
2. var I:integer; D:Double; ch:char;
3. begin
4.   Randomize;
5.   for I:=1 to 20 do
6.     begin
7.       D:=Random()*1000;
8.       writeln(D:8:3,'   ',RoundTo(D,3):8:3);
9.     end;
10.   ch:=Readkey;
11. end;    
12.  

B

[wp]

RoundTo is a bit counterintuitive. Look at the help file:

function RoundTo(
  const AVAlue: Extended;
  const Digits: TRoundToRange
):Extended;

"RoundTo rounds the specified float AVAlue to the specified number of digits and returns the result. This result is accurate to "10 to the power Digits". It uses the standard Round function for this."

The key to understanding is the phrase "10 to the power Digits". This means that if you use the Digits parameter 3 the result is rounded to thousands (10^3). Since your numbers are only between 0 and 1000, the rounded result will be only 0 or 1000. Just increase the multiplier of the random() function from 1000 to 10000 to see that it always rounds to multiples of 1000.

I suppose you want to round the value to 3 decimal places. In this case the Digits parameter must be -3 (--> 10^-3).

Code: Pascal  [Select][+][-]

1. program MakeRoundTos;
2. uses
3.   Math;
4. //  SysUtils;
5. var
6.   I:integer;
7.   D:Double;
8.   ch:char;
9. begin
10.   Randomize;
11.   for I:=1 to 20 do
12.     begin
13.       D := Random()*1000;
14.       writeln(D:8:3, '   ', RoundTo(D,-3):8:3);   // <--- -3 instead of 3 !
15.     end;
16.   ReadLn;
17. end.

[Bazzao]

Thanks wp.

The help could be a bit more helpful. Including 2 examples, one positive and one negative.

It appears this is the opposite to Round*() in other languages, where a positive is used for decimals and negative for integers. And that is why help documentation should include opposite examples.

B

[wp]

Write a bug report and request it.