Binary to Decimal notation?

Question

I am doing Eloquent JavaScript and i am at the part of correlation, so far, I got the values here but don't know how to place the index on an array,

n00 = 76 (no squirrel, no pizza) 
n01 = 9 (no squirrel, pizza) 
n10 = 4 (squirrel, no pizza) 
n11 = 1 (squirrel, pizza)

but I don;t get how to place its' indexes, and i found the annotated version, here it is:

00 → 0   // Both digits are 0. 0 + 0 = 0.
01 → 1   // There’s a 1 in the 20 position. 0 + 20 = 1. - I don't get this 20s
10 → 2   // There’s a 1 in the 21 position. 21 + 0 = 2 - I don't get this
11 → 3   // There’s a 1 in both spots. 21 + 20 = 3. - I don't get this

So our array should look like this:

[76, 9, 4, 1]

How did this happen? why 20s? please help me understand,

I think it is 2 to the power 0 and not 20, same for 21(2 to the power 1). — Himanshu Tanwar
– Himanshu Tanwar, Commented May 31, 2016 at 9:49

Sergio Tulentsev · Accepted Answer · 2016-05-31 09:58:26Z

2

It's not 20, it's 2⁰. And, similarly, 2¹ instead of 21.

11 → 3 // There’s a 1 in both spots. 2¹ + 2⁰ = 3

2¹ is 2.
2⁰ is 1.
2 + 1 = 3. See?

Must be formatting problem in the original material.

Update:

It is a formatting problem in the question, not the original material. Here's the piece from the annotated version:

Indexes of bits in binary representation (which also serve as values for powers of 2) start from right to left, with 0 being the rightmost index.

edited May 31, 2016 at 9:58

answered May 31, 2016 at 9:50

Sergio Tulentsev

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