#ifndef
        
        #ifndef — 
      Conditional reading of code.
                
       
      
        
        Description
        
      If the specified macro is not defined then #ifndef can
    incorporate text into an orchestra upto the next
    #end.  
    This is similar to, but independent of, the macro system in the score
    language.
    
       
      
        
        Syntax
        #ifndef NAME
        ....
        #else 
        ....
        #end 
       
      
        
        Performance
        
      Note that the #ifndef can be nested, like in the C preprocessor language.
    
       
      
      
        
        Credits
        
      
        
          
            | Author: John ffitch | 
          
            | University of Bath/Codemist Ltd. | 
          
            | Bath, UK | 
          
            | April 2005 | 
        
        
    
        New in Csound5 (and 4.23f13)