Null Return for a Module

[Dave the Funkatron]

Hi all,

I'm getting strange output and am trying to track down what might be
causing it. I have the following code in my .nb file:

(* begin code *)

Test[ ] := Module[ {i, thesum},
thesum = 0;
For[ i = 1, i <= 3, i++,
thesum = thesum + i
]
Return[ thesum ]
]

Test[ ]

(* end code *)

The output I would expect would be simply

6

But, I get

Null Return[6]

Alternatively, if I change the last line of the Test function to be

thesum

instead of

Return[ thesum ]

I get

6 Null

as the output. If I remove the for loop, I get expected behavior,
i.e.,

Test[ ] := Module[ {i, thesum},
thesum = 1 + 2 + 3;
(*
For[ i = 1, i <= 3, i++,
thesum = thesum + i
]
*)
Return[ thesum ]
]

yields the output

6

as one might expect. I'm not sure what this all means, or what it is
complaining about. I have other for-loops that are apparently working
properly. So, can anyone give me an idea what might be going wrong
here?

Thanks.

Dave

[Szabolcs Horvát]

Dave the Funkatron wrote:
> Hi all,
>
> I'm getting strange output and am trying to track down what might be
> causing it. I have the following code in my .nb file:
>
> (* begin code *)
>
> Test[ ] := Module[ {i, thesum},
> thesum = 0;
> For[ i = 1, i <= 3, i++,
> thesum = thesum + i
> ]
> Return[ thesum ]
> ]
>

You forgot a semicolon. The newline after For[] was interpreted as
multiplication. The correct version is

test[ ] := Module[ {i, thesum},

thesum = 0;
For[ i = 1, i <= 3, i++,
thesum = thesum + i

]; (* <--- note the semicolon *)
Return[ thesum ]
]

[Jens-Peer Kuska]

Hi,

try

Test[] := Module[{i, thesum}, thesum = 0;

For[i = 1, i <= 3, i++, thesum = thesum + i]; (* <= Here *)
Return[thesum]]

For[] return Null and since you have forgotten the CompoundExpression[] ";"

the result is interpreted as a product For[__]*Return[_]
and since Return[] does not work in expressions, you
get Null*Return[6]

Regards
Jens

[Helen Read]

Dave the Funkatron wrote:
> Hi all,
>
> I'm getting strange output and am trying to track down what might be
> causing it. I have the following code in my .nb file:
>
> (* begin code *)
>
> Test[ ] := Module[ {i, thesum},
> thesum = 0;
> For[ i = 1, i <= 3, i++,
> thesum = thesum + i
> ]
> Return[ thesum ]
> ]
>
> Test[ ]
>
> (* end code *)
>
>
> The output I would expect would be simply
>
> 6
>
> But, I get
>
> Null Return[6]

You are missing a semi-colon. Try this:

Test[] := Module[{i, thesum},
thesum = 0;
For[i = 1, i <= 3, i++, thesum = thesum + i];
Return[thesum]]

--
Helen Read
University of Vermont

[W_Craig Carter]

Hello Dave the Funkatron,
I believe you have a missing ";"
Try

Test[] := Module[{i, thesum}, thesum = 0;
For[i = 1, i <= 3, i++, thesum = thesum + i] ;
Return[thesum]]

Test[]