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Validating a user's input to make sure it's in binary (C++)

Answer 1

+5 A:

Assuming you use std::string:

while( str.length()==8 && str.find_first_not_of("01")==std::string::npos )

that is, if you really want it to be always 8 characters. Adjust to suit your taste (for what I can tell by your comment, you want str.length()<=8 or (!str.empty()) && str.length()<=8.

Michael Krelin - hacker 2009-09-27 20:14:30

This works for rejecting something like 1111111111but not for 11111100000000.

danny z 2009-09-27 20:25:01

danny z, I'm not sure what you're trying to say. Your both examples will be rejected because they're longer than 8 characters.

Michael Krelin - hacker 2009-09-27 20:27:22

What I meant was I just wrote the loop and checked it and it didn't reject 1111110000000

danny z 2009-09-27 20:29:34

I've just tried it, and (not surprisingly) it works for me.

Andy 2009-09-27 20:35:01

danny z, obviously the code above could not possibly accept `1111110000000`, so the bug is not in the condition. Feel free to show your code if you can't find the error.

Michael Krelin - hacker 2009-09-27 20:46:31

yeah the error has to be here: while(!input.empty() input is the string which contains the binary number.Thanks again for the help guys

danny z 2009-09-27 20:48:47

danny_z Have you noticed parentheses around `!input.empty()` in my example? Also, why `8.` - is it float?

Michael Krelin - hacker 2009-09-27 20:53:12

I added the parentheses just now, and the . was a typo. sorry this is taking forever I've been coding all morning im starting to slip up with small mistakes. Here's a question: should this be a while or do while loop. I had this in a do while and I'm thinking I really shouldn't have

danny z 2009-09-27 20:58:26

Well, it's a question for you, not for me ;-) It is `while()` if you have input before you enter the loop and want to handle the situation where the first line is already invalid. It is a `do-while()` if you only know exit condition by the time you're done with iteration. It does look more like `while()` or even `for()` (depending on your input machinery) to me.

Michael Krelin - hacker 2009-09-27 21:11:00

My original thought was:do{take input} while (input isnt right)yet with the condition i just posted, this is still not working ;[

danny z 2009-09-27 21:15:44

`do { take input } while (input isn't right)` meaning you want to skip invalid lines first? In this case you, of course, need to revert condition: `input.empty() || input.length()>8 || input.find_first_not_of("01")!=std::string::npos`

Michael Krelin - hacker 2009-09-27 21:21:43

Thanks so much. After taking a nice break after coding all day this mistake was so clear it wouldn't have warranted a stackoverflow post, but thanks again.

danny z 2009-09-28 00:59:07

;-) you're welcome.

Michael Krelin - hacker 2009-09-28 05:47:59

Answer 2

A:

I would suggest you to use std::bitset

if you string is always contain bits i.e. only **0 and 1 you u can use**

bitset<8> bitOfStr(string("01011")); // initialize from string bitset<8> bitOfStr(YourStringhere);

Note: If string contain anything else then 0/1 before length of bitset it will through an exception.

on bitset You can perform your rest of operations more efficiently .

sat 2009-09-28 05:53:07

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