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[sleeping_sun]

How do u write pi=3.14 on freebasic?

[Gonzo]

in C it would be "const float PI = 3.141592..."
in FB its almost the same:

Code: Select all

Const As Double PI = 3.14159265357989
or
Const As Single PI = 3.14159265

[vdecampo]

I use...

Code: Select all

#Ifndef PI
     #define PI     ATN(1)*4
#Endif

-Vince

[sleeping_sun]

Thank u guys :)

[KristopherWindsor]

I use...

Code: Select all

#Ifndef PI
     #define PI     ATN(1)*4
#Endif

-Vince

You need additional parenthesis there, otherwise PI^PI won't evaluate correctly. Or you could just make it a const.

[Richard]

If you use Atan2(0,-1) instead of 4 * Atn(1) then you don't need the brackets!
I sometimes use the following in FB.

Code: Select all

Const As Double Pi = Atan2(0,-1)

[rolliebollocks]

@Vince

Won't using the ATN in a macro recall that slow trig func for every PI calculation?

[qbworker]

If you don't need anything manually deallocated, just use:

Code: Select all

if multikey(&h01) then end

[pestery]

Won't using the ATN in a macro recall that slow trig func for every PI calculation?

No. The compiler evaluates constants when compiling, so in the code you see (Atn(1)*4) but when the program runs it has been simplified by the compiler to 3.141... Or at least that's what the speed test I just did suggested.

[jevans4949]

You could make use of the fact that the Intel Floating Point Maths Unit will return you the value of pi.

Code: Select all

function pi as double
    asm
        fldpi
        fstp qword ptr [function]
    end asm
end function
  
    
print pi
Dim pi2 As Double = 2*pi
Print pi2
Sleep
    

[vdecampo]

You could make use of the fact that the Intel Floating Point Maths Unit will return you the value of pi.

Code: Select all

function pi as double
    asm
        fldpi
        fstp qword ptr [function]
    end asm
end function
  
    
print pi
Dim pi2 As Double = 2*pi
Print pi2
Sleep
    

Yes but the function call overhead would kill any speed.

-Vince

[MichaelW]

For CRTs, math.h almost invariably defines it as the 21-digit constant:

#define M_PI 3.14159265358979323846

[jevans4949]

You could rename my function "setpi" and then

dim pi as double = setpi

However, I just checked whether there were any differences, and with doubles the results of all three formulae are identical. I guess any difference is lost in the rounding from extended precision, which in our case we have not got.

[sleeping_sun]

why dim pi as double?

[jevans4949]

Single-precision floating point has a precision of about 6 decimal digits. Double precision has about 15 decimal digits. Most people prefer the longer precision for calculation, especially if the variables in question are subject to multiple calculations.

Single precision is appropriate if you are storing results derived from outside sources which are not recorded with such accuracy - e.g., weather temperatures.

A while back, I worked on a database where we stored data in published company accounts, which are usually only reported to this sort of precision. If we tried to reproduce the balance sheets, they rarely balanced.