Program that converts the Binary string to the Numeric

Python Help
1

b=‘1111’

i=0

while b:

i = i*2+(ord(b[0])-ord(‘0’))

b=b[1:]

print(‘Decimal value’+ str(i)

Can anyone explain what does ord(b[0]) do here?

2

This is a great thing to play around with in the REPL - the Python command-line interpreter. Start by looking at it one piece at a time.

>>> b='1111'
>>> b[0]
'1'
>>> ord(b[0])
49

So… what does ord() do? Let’s have a look at its documentation. (You can see this interactively by typing help(ord) - note that you aren’t calling ord here, you’re passing it as a parameter to the help function.)

Help on built-in function ord in module builtins:

ord(c, /)
    Return the Unicode code point for a one-character string.

Does that answer the question? If not, here’s a video from Computerphile about the basics of Unicode: https://www.youtube.com/watch?v=MijmeoH9LT4 What the ord() function does is take a character and give you its number; there’s a corresponding chr() function which takes a number and gives you back the character.

Hope that’s a start!

3

Hey Chris bro! Now i understood after reading this twice:
b=‘1111’

b[0]
‘1’
ord(b[0])
49

I learnt C++ so now i understood this shit lol thanks m g!

1 Like
4

Bro can you please tell me why we have used i*2?

5

This is part of the concept of place value - since you’re working in binary, each place is worth 10 (binary) or 2 (decimal) times the previous place. Try working through things manually and see it happen. If you were to multiply by 10 (decimal) instead, you would get the number represented by a string of decimal digits; if you were to multiply by 10 (octal) or 8 (decimal), you’d get the number represented by a string of octal digits; etcetera.

1 Like
7

Each time through the loop, what values do you see for i if you test it? Do you see how that relates to the b input?

Let’s say I have a value i that represents the converted result for 100, and then I want to get the result for either 1000 or 1001 (both of the 4-bit binary strings starting with 100). How will the result for 100 help us here? What steps would you take, in order to compute the rest of the result? Can you see why multiplying by 2 would be helpful? (Hint: what’s another name for “binary”?)

1 Like
8

As an aside, note that Python has the ability to do binary-decimal conversions inbuilt. int() accepts two parameters, with the second specifying the number base to use. int("1111", 2) == 15. Of course that doesn’t help with understanding how such a conversion actually works.

1 Like
10

Got it Spencer! Thanks!

11

This explanation was the best, Karl! Thanks a ton!