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I need to perform a number of operations within a For loop and store the results in an indexed array (without using the Append function) For examole (to make it simple), I need to find the square of numbers i = 1 to 5 and sore it in y[i]. In precedural languages it would look like:

   for i = 1,5,i++,
        y(i)=i^2
    end

To implement this in Mathematica I tried this code:

 For[i = 1, i <= 5, i++,
    y[[i]] = i^2;  
    ]

which failed. Is there a way to create such array (y)?

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    $\begingroup$ Do you understand why it failed? y is not defined, so you can't access y[[i]]. Try defining y before and it works (for that, see e.g. ConstantArray). Edit My comment assumes, as you state, that you need to use For. Otherwise that's much simpler with Table. $\endgroup$ – anderstood Mar 23 '18 at 16:44
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    $\begingroup$ You almost never need a For[] loop. Try y = Range[5]^2. $\endgroup$ – J. M. is away Mar 23 '18 at 16:44
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    $\begingroup$ Or lookup Table. $\endgroup$ – gwr Mar 23 '18 at 16:45
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    $\begingroup$ Then you should look up Map[] or Table[] as already suggested, if you have a list of images. If you really must loop, use Do[] instead. $\endgroup$ – J. M. is away Mar 23 '18 at 17:09
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    $\begingroup$ If OP is doing image processing OP should probably be using at least some of Mathematica's image processing functions: Blur, a whole host of Filters, etc. $\endgroup$ – High Performance Mark Mar 23 '18 at 20:33
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y = Range[5]; (* y needs to be predefined as anderstood pointed out *)
For[ i = 1, i <= 5, i++,
  (* body *)
  y[[i]] = i^2
]

If it has to be For...

y
(* {1, 4, 9, 16, 25} *)
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  • $\begingroup$ Thank you so much! $\endgroup$ – Heba Sea Mar 23 '18 at 16:52
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    $\begingroup$ @HebaSea You are welcome. Be sure to look up the alternatives given in the comments above. For really is no fit for Mathematica. $\endgroup$ – gwr Mar 23 '18 at 16:56

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