How do I debug this code?

Hello everyone,

I was given the code depicted below which contains 5 erros, I was able to debug the 1st and last errors or warning messages. The other warning messages are related to Preallocation of Variables, and that's where I am struggling. Your help would be appreciated.

clear all;
close all;
clc;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% ask user for zip code
code = input('Please enter the Postal Bar Code: ','s');
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% break the zip code into segments of 5 and convert to the appropriate
% number
zip = '';                                   % empty initial zip code
digit_code = '';                            % empty initial digit
for k = 1:length(code)                      % go through all valid bars
    digit_code = [digit_code code(k)];      % get next digit
    if length(digit_code) == 5              % if 5 bars collected
        switch digit_code                   % determine number from barcode
            case '...II'
                number = '1';
            case '..I.I'
                number = '2';
            case '..II.'
                number = '3';
            case '.I..I'
                number = '4';
            case '.I.I.'
                number = '5';
            case '.II..'
                number = '6';
            case 'I...I'
                number = '7';
            case 'I..I.'
                number = '8';
            case 'I.I..'
                number = '9';
            otherwise
                number = '0';
        end
        if count <= 8                           % if value is a part of the zip code
            zip = [zip number];                 % add digit to 
            count = count + 1;                  % update count
            digit_code = '';                    % reset digit
        else                                    % if value is the error check value
            error_val = number;                 % store error check value
        end
        if count == 5
            zip = [zip '-'];                % add dash after 5 digits
        end
    end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% check for errors in reading bar code
% sum zip digits
zip_sum = 0;                                            % initialize sum
for k = 1:10
    if k ~= 6
        zip_sum = zip_sum + str2num(zip(k));            % add each digit
    end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% check for error
if mod(error_val+zip_sum,10) ~= 0
    fprintf('There is an error in the Postal Bar Code.  Zip code cannot be determined.\n');
else
    fprintf('The zip code is %i.\n',zip);
end

[Athrey Ranjith Krishnanunni]

It would help to know the complete error/ warning messages, with line numbers and the exact text.

[Edivaldo Bartolomeu]

Hi ARk,

Thanks for replying.

Line 24: The variable 'digit_code' appears to change size on every loop iteration. Consider preallocating for speed.

Line 49: The variable 'zip' appears to change size on every loop iteration. Consider preallocating for speed.

Line 56: The variable 'zip' appears to change size on every loop iteration. Consider preallocating for speed.

[Athrey Ranjith Krishnanunni]

Well, it would have been better to know which line is 24, 49, or 56, but in this specific context, I can take a guess. In the future, please specify the offending line numbers in the code itself (as comments).

As to what to do, I don't think preallocation would be of any significant help, because the array size doesn't grow by a lot, and it would be too much trouble for you to rewrite your code to include preallocation.

You can suppress the messages by typing

%#ok<AGROW>

at the end of each offending line.

[Edivaldo Bartolomeu]

Alright, thanks for helping mate.

Answer 1

[Cris LaPierre]

Preallocation messages are code analyzer warnings, not errors. They are tips to improve your code, but will not prevent it from running.

[Edivaldo Bartolomeu]

Thanks for helping Cris.