How to make error checking for each element in array?

Question

lbon jbn 2011-11-30

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https://ww2.mathworks.cn/matlabcentral/answers/22725-how-to-make-error-checking-for-each-element-in-array

Hello guys, I am trying to get Matlab to check for errors for an input. The input can be entered in as an array and I would like for it to check each element if it is a negative value or non-numerical.

Here is what I have so far, it works if only a single number is entered but otherwise it crashes.

function [ volume ] = cube( a )
%p=imread('cubepict.png');
         %imshow(p)
               repeat = 1;
               while repeat ==1
             a = input ('Please enter a value or values for a according to the diagram: ', 's');
             if any(~isnan(str2double(a)))
                 a = any(str2double(a));
              end
              if any(a < 0) |any(ischar(a))
                 disp ('Input(s) must be numerical and cannot contain negative values. Please try again.')
              else repeat=0;
              end 
               end
             fid=fopen('cubelength.txt','w') ;
             fprintf(fid, '%1.2i',a);
             fclose(fid);
             load cubelength.txt;
             volume = a.^3;   
               fid2=fopen('volume.txt','w');
               fprintf(fid2,'%1.2i',volume);
end

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Answer 1

Walter Roberson 2011-11-30

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在 MATLAB Online 中打开

After you read "a" but before you do anything else to it:

a = regexp(a, ' ', 'split');

This will turn "a" in to a cell array of strings. This is needed because str2double() can only return one value per input string but is happy to do that for each cell array member.

Warning: your line

a = any(str2double(a));

is badly broken. It will set a to the scalar value 1 if at least one field in the input was a number, and will return 0 if the input was empty or if all of the fields in the input were non-numbers. Thus will thus turn the array of values in "a" in to a single (logical) value, which will not be useful for further processing.

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Walter Roberson 2011-12-1

What you need to know for that message is whether any of the conversions failed or resulted in a value less than 0.

You will find this logically easier to process if you do not keep overwriting a.

A_num = str2double(a);

if any(isnan(A_num)) || any(A_num < 0)

%complain, and then "continue" the loop

end

You will find that you can use this right after "a" has been split in to strings.

lbon jbn 2011-12-1

It still does not accept arrays...

Here is the updated code:

function [ volume ] = cube( A )

p=imread('cubepict.png');

imshow(p)

repeat = 1;

while repeat ==1

a = input ('Please enter a value or values for a according to the diagram: ', 's');

a = regexp(a, ' ', 'split');

A_num = str2double(a);

if any(~isnan(A_num)) || any(A_num < 0)

disp ('Input(s) must be numerical and cannot contain negative values. Please try again.')

else repeat=0;

end

fid=fopen('cubelength.txt','w') ;

fprintf(fid, '%1.2i',A_num);

fclose(fid);

load cubelength.txt;

volume = A_num.^3;

fid2=fopen('volume.txt','w');

fprintf(fid2,'%1.2i',volume);

end

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Answer 2

lbon jbn 2011-12-1

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https://ww2.mathworks.cn/matlabcentral/answers/22725-how-to-make-error-checking-for-each-element-in-array#answer_29924

I was checking it out again and it seems like it still does not recognize the input are a numerical response and therefore gives the error message I programmed into it. Some how the conversion is failing.