value := sin (pi) ?????

[Fred vS]

Hello.
If i do
value := sin (pi) or
value := sin (2*pi)
i get value = -5.32533 or 2.7689, it depends of the feeling of the pc.....???
In my old trigonometric book, sin(pi/2)=1, sin(pi)=0, sin(2*pi)=0.
Everything changes, trigonometric also ????

[typo]

Code: [Select]

var
  R: Extended;
  S: string;
begin
  R := Sin(Pi);
  Str(R:5:3, S);
  ShowMessage('The Sin of Pi is ' + S);
end;     


[Fred vS]

Hello
@ typo : thanks 

[faber]

IMHO

Code: [Select]

Writeln (Sin(Pi):0:1); should prints 0.0.
Do you also have other result ? (I've -0.0). fpc bug ?!

[User137]

At first glance it seemed like you might be looking at exponent 10 format.
-5.10e-10 actually means close to 0.000000051~whatever.

This is good old way to ensure it has proper decimals:

Code: [Select]

S:=format('%.2f',[sin(pi)]);

[Fred vS]

@faber

(I've -0.0). fpc bug ?!

I get the same result too....

[typo]

sin(pi/2)=1, sin(pi)=0, sin(2*pi)=0.

[Leledumbo]

I get the same result too....

Floating points have two representations of zero because it have sign bit (just like the old one's complement for integers), so both -0.0 and 0.0 are correct.