Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles.

Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.

• Implement the conversion yourself. Do not use something else to perform the conversion for you.

Decimal is a base-10 system.

A number 23 in base 10 notation can be understood as a linear combination of powers of 10:

• The rightmost digit gets multiplied by 10^0 = 1
• The next number gets multiplied by 10^1 = 10
• ...
• The nth number gets multiplied by 10^(n-1).
• All these values are summed.

So: 23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10

Binary is similar, but uses powers of 2 rather than powers of 10.

So: 101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10.

Execute the tests with:

$ mix test

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-

It's possible to submit an incomplete solution so you can see how others have completed the exercise.