#IFDEF - Learn To Code - PlayBASIC Documentation

#IFDEF

#IFDEF <..Expression..>

Parameters: NONE

Returns: NONE

#IFDEF and #IFNDEF are similar to the #IF directive. It is also used in conjunction with #ELSE and #ENDIF and evaluated during compile time. It allows you selectively define sections of code that should be compiled, or be ignored.

The difference is that #IFDEF returns True if a specified variable was previously defined, and #IFNDEF returns False if a specified variable was not defined.

Example

  Var1 = 12
; Var2 = 0

  #IFDEF Var1
  Print "Var1 is defined"
  #ENDIF

  #IFNDEF Var2
  Print "Var2 is NOT defined
  #ELSE
     Print "Var2 is defined
  #ENDIF

  Sync
  WaitKey

#IF/#ELSE/#ENDIF

Previously with the #IF/#ENDIF we've only been able to selectively compile one section code when the #IF expression is TRUE. However some times you need to selectively choose between two sections of code to compile. With the #ELSE directive, we gain this control.

Depending upon the #IF expression is TRUE OR FALSE, will determine which section of code is compiled. So logically, when the #IF condition is TRUE, the code between the #IF and #ELSE directives is compiled. But when #If the condition is FALSE, the code after the #ELSE and between the #ELSE-#ENDIF is compiled.

Example

  Constant Mode = 0

  #IF  Mode=0
     Print "This Program Was compiled in Mode Zero"
  #ELSE
     Print "This Program Was compiled in some other Mode"
  #ENDIF

This example would display (bellow), since the condition (Mode = 0) is True. Notice how the code between the #ELSE/#ENDIF is not compiled. So only the code between the #IF/#ELSE will exist in the compiled program.

  This Program Was compiled in Mode Zero


Related Info:	#Abort \| #ENDIF \| #IF \| #IFNDEF \| #Warn \| Comparisons :