Is this a bug?

[Nicola]

Hi.
You've probably discussed this before, but I've happened to see a result that looks anomalous.
If I take the square root of 25, for example, the result is different from the integer (INT) of the result itself. While if I do the result of the root minus the integer of the result itself, exactly 0 comes out.
I am attaching the program with which I tested the anomaly.
Why does this happen?

Code: OxygenBasic

1. include "$/inc/console.inc"
2. dim b as double
3.  
4. while 2
5. printl "input a number: "
6. int a=input()
7. b = sqrt(a)
8. printl "a           = " a
9. printl "b = SQRT(a) = " b
10. printl "INT(b)      = " int(b)
11. if b=int(b) then
12.         printl "1) b  = int(b)"
13. else
14.         printl "1) b <> int(b)"
15. end if
16.  
17. printl
18.  
19. if b - int(b) = 0 then
20.         printl "2) b  = int(b)"
21. else
22.         printl "2) b <> int(b)"
23. end if
24.  
25. waitkey
26. loop
27.  

This is the result of the tests:

input a number: 25
a                  = 25
b = SQRT(a) = 5
INT(b)          = 5
1) b <> int(b)
2) b  = int(b)

input a number: 63
a                  = 63
b = SQRT(a) = 7.9372539331937721
INT(b)          = 8
1) b <> int(b)
2) b <> int(b)
(same result, ok)

[Charles Pegge]

Hi Nicola,

int(n) is an uncaught error. You can have trunc() round() floor() ceil()

[JRS]

FYI:

This forum supports code syntax highlighting.

Use code=o2 for OxygenBasic.

[Nicola]

@Charles
Ok, but why is it okay if I do the subtraction?

[Charles Pegge]

I'm not sure, but in general it is unsafe to compare integers and floats in a conditional. It is also unsafe to compare floats with floats for equality where expressions are involved.

You could use  frac() to look at the fractional component of a float, as well as trunc() to get the integer component.

Code: [Select]

b=sqrt(a0
if frac(b)
  ...
else 'no fraction
 ...
endif

Also ear in mind that square roots could be negative as well as positive.

[JRS]

Hi Charles,

Does O2 have a DO keyword? I was looking for a WEND with that WHILE  and then noticed the LOOP.

[Charles Pegge]

Yes John, we have do ..exit do..continue do.. end do / loop for unconditional loops

[JRS]

So it's okay to use a DO keyword (LOOP) with a WHILE?

[Charles Pegge]

Yes, you can use  loop to close a while block instead of wend, but I would not recommend it.

[Nicola]

@Carles

Also ear in mind that square roots could be negative as well as positive.

Hi.
Yes, in the context of R, there is its result and its negative opposite whose square is the radicand. Or, the square root of a negative number has its result in scope C (complex numbers, consisting of a real part and an imaginary part) (for further information, https://en.wikipedia.org/wiki/Square_rootA may be useful )

[Charles Pegge]

Speaking of complex squares, we have a number of Julia and Mandelbrot fractal examples scattered around.

Here are some fractal snaps based on various coloration settings:

https://get.google.com/albumarchive/100574392421270527709/album/AF1QipM9V1gc443sziQHkajKNSYjQ8P7nisjz__bku09

https://get.google.com/albumarchive/100574392421270527709/album/AF1QipPp5wgIYv-dkA-TD-3tGuUfLcQRFDScoE5hmtNt

[JRS]

Nice fractals!

My Favorite

[Nicola]

Really beautiful these fractals. 

... Speaking of strange things ... I was trying various systems to see how to evaluate if the result of the square root of a number n proves that it is a perfect root. Well, after some tests, when it prints the input number on the screen (printl a) some strange characters (-???<) come out ... Why?

Code: Text

1. 'is this a bug?
2.  
3. include "$/inc/console.inc"
4.  
5. dim a,b as double
6. global r as int
7.  
8. sub _print()
9. ====================================
10.         if r=1 then
11.                 printl "YES is an exact root"
12.         else
13.                 printl "NO it is not an exact root"
14.         end if
15.         printl
16.         r=0
17. end sub
18.  
19.  
20. '====== MAIN ===============
21. do
22.  
23. r=0
24. printl "input a number: "
25. 'a=input()
26. a = ltrim rtrim Input ' per togliere caratteri da input tipo CR
27. if a=0 then exit do
28. b = sqrt(a)
29. printl "a       = " a
30. printl "SQRT(a) = " b
31.  
32. printl "Text if the result = INT(result)"
33. if b=int(b) then
34.          r=1
35. end if
36. _print
37.  
38. printl "Text if the FRAC(result) has a fractional component"
39. if frac(b)=0 then
40.         r=1
41. end if
42. _print
43.  
44. printl "Text if result = TRUNC(result)"
45. if b=trunc(b) then
46.         r=1
47. end if
48. _print
49.  
50. printl "Test if Result - INT(result) = 0"
51. if b - int(b) = 0 then
52.         r=1
53. end if
54. _print
55.  
56. printl "Test if INT(Result)^2 = number in input"
57. if int(b)*int(b) = a then
58.         r=1
59. end if
60. _print
61.  
62. loop
63.  
64.  

note: using FRAC (), TRUNC () or B-int (B) the result is ok.

[Charles Pegge]

Hi Nicola, It works as expected. I don't see any question marks on my system. (using o2 version 0.2.9).

[Nicola]

Hi Charles.
This is the version I use (see attached image).
However you have to take the test several times. The problem arises from the sixth input.