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Re: strange behavior

  • To: mathgroup at
  • Subject: [mg104837] Re: strange behavior
  • From: Bill Rowe <readnews at>
  • Date: Wed, 11 Nov 2009 04:28:36 -0500 (EST)

On 11/10/09 at 5:58 AM, Jason_member at (Jason Winters)

>Hi!  I am wondering why these two modules behave differently

>Module[{ans = ""},
>For[i = 1, i < 10, i++,
>ans = InputString["Enter a String"];


>Module[{ans = ""},
>For[i = 1, i < 10, i++,
>ans = InputString["Enter a String"]

>One prints out a bunch of extraneous Null's

The difference is the ; following the For loop. With the
semicolon present, you have a compound expression. When
Mathematica encounters a compound expression, the output is the
result of evaluating the portion following the last semicolon.
In this case, a Print statement.

Without the semicolon, Mathematica does a multiply operation.
That is For[...] Print[...] is seen as a directive to multiply
the results of evaluating For[...] by the results of Print[...].
The output of a For loop is Null which explains the results you got.

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