How to sum strings digits?

Question

Aymen Jassam 2016-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/291815-how-to-sum-strings-digits

回答： yousef salah 2019-3-12

采纳的回答： Stephen23

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How can I sum these numbers . and return the result in string datatype without loosing the precision.

'9437256976162618652738646244869425874869', '776357087634731721006'

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Answer 1

Stephen23 2016-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/291815-how-to-sum-strings-digits#answer_226438

编辑：Stephen23 2016-6-23

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Use John D'Errico's excellent FEX submission, Variable Precision Integer Arithmetic:

http://www.mathworks.com/matlabcentral/fileexchange/22725-variable-precision-integer-arithmetic

>> A = vpi('9437256976162618652738646244869425874869')
A =
    9437256976162618652738646244869425874869
>> B = vpi('776357087634731721006')
B =
    776357087634731721006
>> A + B
ans =
    9437256976162618653515003332504157595875

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Guillaume 2016-6-23

As per Stephen's comment to Shameer answer, you cannot convert the string to number (double or uint64) simply because these numbers are much much too big to be represented in numeric formats without loss of precision.

Muhammad Usman Saleem 2016-6-23

Thanks

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Answer 2

Shameer Parmar 2016-6-23

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 a = '9437256976162618652738646244869425874869';
 b = '776357087634731721006';
 c = num2str(str2num(a) + str2num(b))

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Guillaume 2016-6-23

编辑：Guillaume 2016-6-23

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Stephen has provided the proper answer. If you're going to provide an answer that is clearly wrong, we'll point it out. Please note, that we do not make any personal attacks, so refrain from doing so.

You clearly do not understand the limitations of double numbers. Because of the difference of magnitude between a and b, your addition does not do anything at all

   a = '9437256976162618652738646244869425874869';
   b = '776357087634731721006';
   aa = str2num(a);
   bb = str2num(b);
   cc = aa + bb;

See that cc is equal to aa:

isequal(cc, aa)

returns true. Adding bb made no difference!

That is because the next double number greater than aa is

>>eps(aa)
ans =
   1.2089e+24

about 1e24 more than aa whereas bb is four orders of magnitude (only 7e20) smaller. bb is so tiny compared to aa that it makes no difference when it's added.

Muhammad Usman Saleem 2016-6-23

+1 for Stephon... Who work freely to point out our mistakes... To me he is one of the great source of learning for all researchers...

Pay respect for your seniors

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Answer 3

Aymen Jassam 2016-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/291815-how-to-sum-strings-digits#answer_226549

Problem solved convert to double each number individually and sum, with respect the rest (carry).

Thanks a lot to all of you

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Stephen23 2016-6-24

编辑：Stephen23 2016-6-24

@Aymen Jassam: converting to double most definitely does not "solve" your original question: while converting to double will give an answer, it does not calculate "without loosing the precision" as your question required. This was demonstrated in Guillaume's comment, and explained in my comment.

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