str2double/str2num

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

Answer 1

[James Tursa]

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

[Tsuwei Tan]

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]

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.