Question

Does it exist a better way to reverse an element of X?

>> X = dec2bin(10)
X = 1010

I did this:

x(i) = num2str(1-str2num(x(i)))

Answer 1

If you want to flip a bit of a numeric value num without converting it first to a character array of '0' and '1', then you can use functions like BITXOR, BITGET, and BITSET (as Andrey also mentions):

num = bitxor(num, 4);  %# Flip the bit in the 4's place (i.e. bit 3)
%# Or ...
num = bitset(num, 3, ~bitget(num, 3));  %# Flip bit 3

However, if you do want to operate on the character array, you could also do this very strange thing:

X(i) = 'a' - X(i);
%# Or ...
X(i) = 97 - X(i);

This works because the characters 'a' and X(i) are first converted to their equivalent Unicode UTF-16 numeric values before the mathematical operation is performed. Since the numeric value for 'a' is 97, then a '0' (numeric value 48) or '1' (numeric value 49) subtracted from 'a' will result in the numeric value for the other. The resulting numeric value on the right hand side of the equation is then converted back to a character when it is placed back in the character array X.