how to change or compliment a particular bit in the binary string?

Hi

I have number like a=50 I want to convert it to binary, then I want to randomly choose the position in a binary string and compliment it Like

a=50

b=dec2bin(a)

b=110010

e.g position=4

b becomes

b=110110

how I perform this. kindly help me

Answer 1

[KSSV]

a=50 ;
b=dec2bin(a) ;
b1=110010 ;
b=str2double(regexp(num2str(b),'\d','match')) ;
pos = 4 ;

b(pos) = 1 ;
% join the numbers 
iwant=str2double(sprintf('%1d',b)) ;

[Mudasir Ahmed]

Thank you so much Sir :)

[Guillaume]

And change the call to dec2bin to output 8 bits instead of just the minimum and the answer is broken because position is defined wrongly.

Also, a simpler way to convert that string of '0' and '1' to number would be:

b = dec2bin(a); %change it to dec2bin(a, 8) and the whole thing is broken 
b = b - '0'; %no need for expensive regexp or str2double

But of course, you may as well not bother and just change the character:

b = dec2bin(a);
b(pos) = '1';

Finally, note that this does not flip a bit, just sets it to 1.

[Massimo Zanetti]

This is quite tricky...

Answer 2

[Guillaume]

Note that in your example b is not 110010 but '110010'. The difference is important, b is an array of character, not a number.

Also note that your usage of position is very unconventional. Usually the bits are numbered from right to left (LSB to MSB) not left to right. This is important because if your represent a with 8 bit, 00110010, with your convention position 4 is a different bit.

Anyway, the simplest way to flip a bit in a number is not to convert it to binary, but simply use bitget and bitset:

a = 50;
bittoflip = 3;  %Using normal convention, not yours, bit 3 is the 3rd rightmost
flippeda = bitset(a, bittoflip, ~bitget(a, bittoflip))

You can easily check that it's done the deed:

>> dec2bin(a) 
ans = 
    110010  
>> dec2bin(flippeda) 
ans = 
    110110

[Mudasir Ahmed]

thank you so much sir

[Image Analyst]

For what it's worth, bitset() was what I thought of also. (+1 vote)

Answer 3

[Massimo Zanetti]

Here it is

a=50;
b=dec2bin(a)

pos = 4;
b(pos) = char(97-double(b(pos)))

[Mudasir Ahmed]

Thank you so much sir :)