how can i give variable name having 2 number of nested loop(i and j) ?

for i=1:3
    for j=1:3
        im(i,j)=%action;
    end
end

while doing same above code i get error as: "Undefined function or variable 'im'." and warning as: "The Variable 'im' appears to change size on every loop iteration. consider preallocating for speed" here my im variable must b im11,im12,im13,im21....im33 how can i give such variable name in matlab

[Stephen23]

Don't create lots of variables with numbers in their names. Although beginners all think that this is a great idea, in fact it will only make slow, buggy, obfuscated code. Stick to using one variable, and use indexing, exactly as the answers will tell you.

[Guillaume]

The above code would not result in the error ""Undefined function or variable 'im'". The code you use must be different.

[Vish]

how to get file name when i take a image file from 'imgetfile'

[Stephen23]

The imgetfile documentation gives this syntax:

[filename, user_canceled] = imgetfile

Does that do what you want? If not, then you need to explain your problem in a lot more detail.

[Akbar Khan]

It is a good idea to initialize a variable before loop to avoid any warning .. however you code will not result in any error during compilation or execution. However is is always a good c programming practice to initialize variables before loops like

im = zeros(3, 3);

[Stephen23]

"...is always a good c programming practice..."

But this is MATLAB, not C. There is no reason why any "good programming practice" in language X has to be good in language Y.

https://www.mathworks.com/matlabcentral/answers/31248-variable-declaration-in-matlab

MATLAB does not require initializing of variables. However preallocating variables is recommended before loops:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

"...variable must b im11,im12,im13,im21....im33 how can i give such variable name in matlab"

Don't do this. Use indexing.

https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[Image Analyst]

Don't worry about the warning but don't give unique names to the variables like im11, im12, im13, etc. For more discussion about this bad idea, see the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

If you want to get rid of the warning, preallocation im with

im = ones(3,3);

before the loop.

[Guillaume]

Well actually, do worry about the warning, particularly as it's trivial to avoid:

im = zeros(3, 3);

before the loops.