Flow-control structures: Difference between revisions

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@@ Line 790: / Line 790: @@
 Remark: Pop11 does not perform "tail call optimization", one has to explicitly use chain.
 =={{header|PureBasic}}==
-===goto===
+===Goto===
 Transfers control to the label referenced.  It is not a safe way to exit loops.
 <lang PureBasic>If OpenConsole()
@@ Line 804: / Line 804: @@
   CloseConsole()
 EndIf </lang>
+===Gosub & Return===
+Gosub stands for 'Go to sub routine'. A label must be specified after Gosub where the program execution continues and will do so until encountering a Return. When a return is reached, the program execution is then transferred immediately below the Gosub.
+Gosub is useful when building fast structured code with very low overhead.
+<lang PureBasic>X=1:  Y=2
+Gosub Calc
+;X will now equal 7
+End
+Calc:
+  X+3*Y
+  Return ; Returns to the point in the code where the Gosub jumped from</lang>
+===FakeReturn===
+<lang PureBasic>Gosub MySub
+Lable2:
+; The program will jump here, then 'end'
+End
+MySub:
+If #PI>3
+  FakeReturn  ; This will simulate the function of a normal "Return".
+  Goto Lable2
+EndIf
+Return</lang>
+If the command Goto is used within the body of a sub routine, FakeReturn must be used to correct the stack or the program will crash.
+===OnErrorGoto===
+This will transferee the program execution to the defined label if an error accrue.
+<lang PureBasic>OnErrorGoto(?MyExitHandler)
+X=1: Y=0
+z= X/Y
+; = a illegal division with zero
+Debug "This line should never be reached"
+End
+MyExitHandler:
+  MessageRequester("Error", ErrorMessage())
+  End</lang>
+===OnErrorCall===
+Similar to OnErrorGoto() but procedural instead.
+<lang PureBasic>Procedure MyErrorHandler()
+  ;All open files etc can be closed here
+  MessageRequester("Error", ErrorMessage())
+  End
+EndProcedure
+OnErrorCall(MyErrorHandler())
+X=1: Y=0
+Z= X/Y
+;This line should never be reached</lang>
 =={{header|Python}}==