Explanation of num2str(x) - '0'

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

Answer 1

[Ameer Hamza]

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]

[Abhinandh V]

nice

[Rik]

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).

Answer 2

[Star Strider]

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

Answer 3

[David Fletcher]

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

[Stephen23]

"num2str(x) - this converts the number to a string"

The output is (for historic reasons) not a string, but is actually a character array.

https://www.mathworks.com/help/matlab/characters-and-strings.html