Explanation of num2str(x) - '0'

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Marvin Ott
Marvin Ott on 7 May 2018
Commented: Rik on 15 Dec 2020
Hi, for my homework I had to split a binary number into it's individual parts. After some tying and research I found out that I can use:
num2str(x) -'0'
I now know that it works but I don't know how it works. Can someone explain it to me?
Thanks in advance.
Marvin

Accepted Answer

Ameer Hamza
Ameer Hamza on 7 May 2018
It works because num2str convert the number into a char array. For example
x = 10001100;
y = num2str(x)
ans =
'10001100'
In computer memory, each character is stored on the basis of its ASCII value. From ASCII table character '1' = 49 (decimal) and '0' = 48 (decimal). Therefore in computer memory y is saved as
y = [49 48 48 48 49 49 48 48]
now when you subtracted '0' = 48 decimal, what you are doing is
[49 48 48 48 49 49 48 48] - 48
which gives you
[1 0 0 0 1 1 0 0]
  2 Comments
Rik
Rik on 15 Dec 2020
Actually chars are Unicode codepoints encoded with UTF-16 in Matlab (doclink). The difference starts to be relevant beyond 127, and starts to matter a lot beyond 0xFFFF (i.e. beyond the basic multilingual plane, which contains e.g. most emoji).

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More Answers (2)

Star Strider
Star Strider on 7 May 2018
Character arrays exist as ASCII or other numeric encodings, so that each letter or other character is assigned a numeric value. In MATLAB, they are then handled as any other numeric array.
So:
zerochar = double('0')
chars = '12345'
numarray1 = double(chars)
numarray2 = numarray1 - zerochar
expands to:
zerochar =
48
chars =
'12345'
numarray1 =
49 50 51 52 53
numarray2 =
1 2 3 4 5

David Fletcher
David Fletcher on 7 May 2018
Edited: David Fletcher on 7 May 2018
num2str(x) - this converts the number to a string
Once converted subtracting '0' subtracts the character code for 0 from all entries. Therefore all zero characters become the actual value of 0, and all one characters become the actual value of 1 (since the ASCII code for '1' is one greater than the ASCII code for '0'). Subtracting 48 (the ascii code for '0' achieves the same thing).
>> '0' - 48
ans =
0
>> '1' -48
ans =
1
  1 Comment
Stephen23
Stephen23 on 7 May 2018
"num2str(x) - this converts the number to a string"
The output is (for historic reasons) not a string, but is actually a character array.

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