Descriptions and Examples for the POV-Ray Raytracer by Friedrich A. Lohmüller
    Conditional Statements -
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  - Conditional
    Statements

  Branching
  #if(...) ... #else ... #end
    > in loops
    - in macros
    - in animations
    - turning on/off of parts
  #switch(...) #case(..) ...
          #range(..) ... #end
    - selection by tables

  Check for Existence
    #ifdef(...) #ifndef(...)
    - Check in include files
    - Defaults in include files

  Loops
 Prechecked, Postchecked,
 Count-controlled, Early-Exit
    #while(...)... #end
    #for(...)... #end
    - Samples:
    - Loops with POV-Ray
    - Loops, Sine, Cosine
    - Random with POV-Ray
                                       

Branching in Loops

Sample for the use of #if ... #else... #end in loops:
a) With a #while loop:
union{
 #local Nr = 0;     // start
 #local EndNr = 20; // end
 #while (Nr< EndNr)
   sphere{ <0,0,0>,0.25
  #if(  Nr/2 = int(Nr/2) )
        // only with even numbers Nr
        texture{ pigment{ color rgb<1,0.65,0>}
                 finish { phong 1}
               }
        scale<1,1.5,1>

  #else // with odd numbers Nr
        texture{ pigment{ color rgb<1,0,0.35>}
                 finish { phong 1}
               }
        scale<1.5,1,1>

  #end // end of "#if( Nr/2 = int (Nr/2)"
  translate<1,0.25,0>
  rotate<0,Nr * 360/EndNr,0>}

 #local Nr = Nr + 1;    // next Nr
 #end // ---------------  end of loop

rotate<0,0,0>
translate<0,0,0>
} // end of union -------------------
a) With a #for loop:
union{
 #local EndNr = 20; // end value
//#for(Var.,Start,End,Step)
 #for (Nr, 0, EndNr-1, 1)
   sphere{ <0,0,0>,0.25
  #if(  Nr/2 = int(Nr/2) )
        // only with even numbersn
        texture{ pigment{ color rgb<1,0.65,0>}
                 finish { phong 1}
               }
        scale<1,1.5,1>

  #else // with odd numbers
        texture{ pigment{ color rgb<1,0,0.35>}
                 finish { phong 1}
               }
        scale<1.5,1,1>

  #end // end of "#if( Nr/2 = int (Nr/2)"
  translate<1,0.25,0>
  rotate<0,Nr * 360/EndNr,0>}

 #local Nr = Nr + 1;    // next Nr
 #end // ---------------  end of loop

rotate<0,0,0>
translate<0,0,0>
} // end of union -------------------
#if ... #else ... #end

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© Friedrich A. Lohmüller, 2010
homepage:http://www.f-lohmueller.de