Ternary operator

[Kernelpanic]

Can one also integrate the declaration of a library into a function?
The reason for the question is that I wrote a small program that allows one to use the tenary operator from C. If you could put the whole thing into a function, it might be useful for Basic. Maybe. 

The Basic-Program:

Code: (Select All)

 
'Aufruf des tenaeren Operators in C - 30. Okt. 2023
 
Option _Explicit
 
'In QB64 mit "Declare Library" wie angegeben
Declare Library "D:\Lab\QuickBasic64\Extern-nicht-Basic\C-Aufruf\tenaerOp"
  Function tenaerOp& (ByVal N As Long, Byval X As Long)
End Declare
 
Dim As Long N, X
 
X = 77
 
Locate 3, 3
Input "Zahl: ", N
 
Locate 5, 3
Print Using "Ausgabe: ###"; tenaerOp&(N&, X&)
 
End

The C part:

Code: (Select All)

//TenaerenOperator von Basic aufrufen - 30. Okt. 2023

#include <stdio.h>
#include <stdlib.h>

long tenaerOp(long eingabe, long x)
{
    long ausgabe;
        
    ausgabe = x > eingabe ? 100 : 200;
    return(ausgabe);    
}

[DSMan195276]

Could you clarify what you're trying to achieve? You don't need C to write that function, the ternary operator is the same as just using an `if` for your usage:

Code: (Select All)

Function tenaerOp&(e As long, x As Long)
    If x > e Then
        tenaerOp& = 100
    else
        tenaerOp& = 200
    End If
End Function

Unfortunately if you want a "real" ternary operator you can't implement that as a function. The ternary operator is only supposed to evaluate one of the true or false paths, not both, but there's no way to achieve that with a function call.

[bplus]

Code: (Select All)

Print Iff$(_Width > _Height, "Landscape View", "Portrait View")
x = 150: e = 200
Print Iff$(x > e, "100", "200")

Function Iff$ (Bool&, true$, false$)
    If Bool& <> 0 Then Iff$ = true$ Else Iff$ = false$
End Function

[Kernelpanic]

I know about "If", but in C, Java etc. the tenary operator is there not for fun.

Again: Can something like this be implemented in a function in QB64?

[DSMan195276]

Again: Can something like this be implemented in a function in QB64?

Not in the way it behaves in languages like C and Java, it would have to be built into the language to work properly. Ex. In C and Java you can do stuff like this:

Code: (Select All)

x = (a != 0)? 20 / a: 0; // Checks that a is not zero before dividing by it

There's no way to implement that correctly with a function. The `20 / a` in the ternary operator is only supposed to be evaluated if `a != 0` is true, but with functions all the arguments are evaluated before the function is called.

[bplus]

Code: (Select All)

For a = -1 To 1
    x = Val(Iff$(a <> 0, _Trim$(Str$(20 / a)), "0"))
    Print x
Next

Function Iff$ (Bool&, true$, false$)
    If Bool& <> 0 Then Iff$ = true$ Else Iff$ = false$
End Function

[DSMan195276]

Code: (Select All)

For a = -1 To 1
    x = Val(Iff$(a <> 0, _Trim$(Str$(20 / a)), "0"))
    Print x
Next

Function Iff$ (Bool&, true$, false$)
    If Bool& <> 0 Then Iff$ = true$ Else Iff$ = false$
End Function

Try it again, but skip the floating point math (where division by zero is technically allowed). Do `20 \ a` and the program always explodes, since it gets evaluated before calling the `Iff$()` function.

[bplus]

Got it! Thanks for the good example.

[Kernelpanic]

Again: Can something like this be implemented in a function in QB64?

Not in the way it behaves in languages like C and Java, it would have to be built into the language to work properly. Ex. In C and Java you can do stuff like this:

Code: (Select All)

x = (a != 0)? 20 / a: 0; // Checks that a is not zero before dividing by it

There's no way to implement that correctly with a function. The `20 / a` in the ternary operator is only supposed to be evaluated if `a != 0` is true, but with functions all the arguments are evaluated before the function is called.

Yes, that obviously does not work. How should such and similar variations be intercepted?
Gets kind of complicated.

Code: (Select All)

 
'Tenaerer Operator , Problem in Funktion - 31. okt 2023
'x = (a != 0)? 20 / a: 0; // Checks that a is not zero before dividing by it
 
Option _Explicit
 
Declare Function tenaererOperator(a As Double, b As Double) As Doeble
 
Dim As Double a, b, x
 
Locate 3, 3
Input "Zahl a: ", a
 
Locate 4, 3
Input "Zahl b: ", b
 
If a <> 0 Then
  x = b / a
Else
  x = 0
End If
 
Locate 7, 3
Print Using "b / a = ##.####"; x
 
Locate 9, 3
If tenaererOperator(a, b) = -1 Then
  Print "Keine negativen Werte!"
ElseIf tenaererOperator(a, b) = -2 Then
  Print "Division durch Null!"
Else
  Print Using "x = ###.####"; tenaererOperator(a, b)
End If
 
End
 
Function tenaererOperator (a As Double, b As Double)
 
  Dim As Double x
 
  If a <> 0 And Sgn(a) = 1 And Sgn(b) = 1 Then
    x = b / a
  ElseIf a <> 0 And Sgn(a) = -1 Then
    x = -1
  ElseIf a <> 0 And b = 0 Then
    x = -2
  Else
    x = 0
  End If
 
  tenaererOperator = x
End Function