How to write a program that selectively picks hexadecimal values from a text file based on bit size?

Hello all! I have a text file that is full of 16bit, 32bit, 64bit, and 128bit hexadecimal values, and I was trying to write a program that asks user the bit-size, then once the size is selected, a random hexadecimal value from the text file is spit out. I was thinking about if statements, but nothing I try is working. Any help or guidance would be greatly appreciated!

Edit Sorry! I have added the text file, but it is 4 hex values per a line, then enter. There are a lot more values than this in the real one but it follows same format

Edit#2

I am mostly confused with syntax for the bit selector, but I was thinking something like:

read file,

user selects bit mode (4 options)

if 16bit --> rand

if 32bit --> rand

if 64bit -->rand

if 128bit -->rand

if anything else, error

[Scott MacKenzie]

It might help if you attach an example file.

[Akana Juliet]

My apologies, here is a shortened versionof the textfile

[Stephen23]

How are the values delimited? What structure does the file have, or is it just one line of values?

Please upload a sample file by clicking on the paperclip button.

[Akana Juliet]

The file is attached here in the comments and I have updated the original. But basically it is 4 values per a line. This text file is a sample and the real one has a lot more, but it will still be 4 hex values per a line, then enter.

[Scott MacKenzie]

So, can we assume the "real" text file simply repeats the organization in the example file? That is, lines 1, 5, 9, etc., contain 16-bit hex values, lines 2, 6, 10, etc., contain 32-bit hex values, and so on? And can we assume the user input is one of 16, 32, 64, or 128?

[Akana Juliet]

@Scott MacKenzie Actually, it's more like

lines 1-20 are all 16bit

lines 21-40 are all 32bit

lines 41-60 are all 64bit

lines 61-80 are all 128bit

Sorry for the lack of context in my question! I hope this helps convey. Thanks so much for helping me

[Scott MacKenzie]

OK thanks. I see that @David Hill has just posted an succinct answer. Good luck.

Answer 1

[David Hill]

r=randi(4);
a=readcell('hextest.txt');
x=input('hex length: ');
hexValue=a{log2(x/16)+1,r};

[Akana Juliet]

Does hexValue=a{log2(x/16)+1,r} tell you which row to randomize from and it goes 1-4? That's a pretty good idea, I could format the rest of the values I have to just one line and keep the entire text file 4 lines.

If I wanted to print 4 random values from the line selected how could I do that?

[David Hill]

Yes. If you don't want any repetitions, use randperm.

r=randperm(4,3);%selects 3 in random order from 1:4
a=readcell('hextest.txt');
x=input('hex length: ');
hexValue=a(log2(x/16)+1,r);%output is a cell array

[Akana Juliet]

Thank you so much for your help @David Hill ! I just have one final question, what am I doing wrong with my print statement? I'm only seeing 1 random value posted?

r=randi(4,3);

a=readcell('anothertest.txt');

x=input('Enter bit length: ');

hexValue=a{log2(x/16)+1,r};

fprintf('%s %s %s\n', hexValue);