What is the correct way of calling a function in a command c: ?

I have learnt Autolisp on my own for several weeks but I am confused with some basics.

I just came up with this weird and clearly redundant piece of code, and when I load it and type "cane" in the console, it shows "nil". When I type "cane" in AutoCAD command prompt, it asks for my radius and then stop. What is the reason for this?

Btw is this a correct way of calling a function in the c: command?

(defun c:cane ()
 (setq radius (getreal "\nEnter radius: "))
 (setq jas (circarea radius))
 (princ jas)
)

(defun circarea (rad)
  (setq n (* pi rad rad))
)

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I've moved your question to the Autolisp section: http://www.cadtutor.net/forum/forumdisplay.php?21-AutoLISP-Visual-LISP-amp-DCL

Nothing is wrong with that result .

You can not run the routine from a console since that it is built as a standalone program that it starts with "c:" so that's why it did return nil.

But if it is started without "c:" it would run as if it is running in the command line as standalone program .

To explain the fore-said with modification on the codes , just remove the c: and load the function again and call it from console to see the difference like this (cane) .

Hope this helps .

I just came up with this weird and clearly redundant piece of code, and when I load it and type "cane" in the console, it shows "nil". When I type "cane" in AutoCAD command prompt, it asks for my radius and then stop. What is the reason for this?

The function is defined with the symbol c:cane, therefore the symbol cane will hold no value when evaluated through the console unless you have assigned a value to this symbol elsewhere.

On evaluating the symbol c:cane at the console, you will see a pointer to the memory address of the function definition:

_$ c:cane
#<USUBR @000000002e6fb930 C:CANE>

You can then evaluate this function at the console as you might any other AutoLISP function:

_$ (c:cane)
4.523894.52389

(The result is duplicated because princ will print the value to the command-line and will then return the supplied value, which is in turn returned by the calling function c:cane since it is the last evaluated expression - you can suppress this duplication by including a (princ) or (prin1) as the last evaluated expression, which will cause a null symbol to be returned).

Prefixing the function symbol with c: has no effect when evaluating the function through AutoLISP, however, this prefix enables the function to be evaluated as a command at the AutoCAD command-line.

You will often see in examples here different ways of defining defuns like (AH:dothis) its the author leaving his/her signature on the code and as Lee said previously type dothis will not work, you have to use the full version (AH:dothis)