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str2double/str2num

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day='0001'; str2double(day) would give me 1 as answer, how do I get 0001 exact four number of digits for instance?

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Accepted Answer

James Tursa
James Tursa on 10 May 2018
Edited: James Tursa on 10 May 2018
Floating point variables do not have leading 0's physically stored in memory (not counting the denormalized numbers of course). So 0001 and 1 are stored exactly the same in memory. If you want to display the leading 0's then you need to use a format that specifies that on print out. E.g.,
>> day = '0001'
day =
0001
>> d = str2double(day)
d =
1
>> fprintf('%04d\n',d)
0001

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Tsuwei Tan
Tsuwei Tan on 10 May 2018
Thank you James! it seems that I have to manually check on my code, since I have some strings like '001', '0001', and '00001' that I have to count how many digits before I fprintf them back to number.
Walter Roberson
Walter Roberson on 10 May 2018
day = '0001';
nd = length(day);
d = str2double(day);
fprintf('%0*d\n', nd, d);
... which leads one to wonder why you do not just print out day instead of the converted value.

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