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.
Decimal is a base-10 system.
A number 23 in base 10 notation can be understood as a linear combination of powers of 10:
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.
defmodule BinaryTest do
use ExUnit.Case
# @tag :pending
test "binary 1 is decimal 1" do
assert Binary.to_decimal("1") == 1
end
@tag :pending
test "binary 10 is decimal 2" do
assert Binary.to_decimal("10") == 2
end
@tag :pending
test "binary 11 is decimal 3" do
assert Binary.to_decimal("11") == 3
end
@tag :pending
test "binary 100 is decimal 4" do
assert Binary.to_decimal("100") == 4
end
@tag :pending
test "binary 1001 is decimal 9" do
assert Binary.to_decimal("1001") == 9
end
@tag :pending
test "binary 11010 is decimal 26" do
assert Binary.to_decimal("11010") == 26
end
@tag :pending
test "binary 10001101000 is decimal 1128" do
assert Binary.to_decimal("10001101000") == 1128
end
@tag :pending
test "invalid binary is decimal 0" do
assert Binary.to_decimal("carrot") == 0
end
@tag :pending
test "invalid binary is decimal 0 II" do
assert Binary.to_decimal("convert01") == 0
end
@tag :pending
test "invalid binary is decimal 0 III" do
assert Binary.to_decimal("10convert") == 0
end
@tag :pending
test "invalid binary is decimal 0 IV" do
assert Binary.to_decimal("1carrot0") == 0
end
@tag :pending
test "22 is not a binary number" do
assert Binary.to_decimal("22") == 0
end
end
ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)
defmodule Binary do
@spec to_decimal(String.t()) :: non_neg_integer
def to_decimal(string) do
binary? = Regex.match?(~r/^[10]*$/, string)
if binary?, do: string |> String.reverse() |> binary_powers(), else: 0
end
defp binary_powers(binary, position \\ 0)
defp binary_powers("", _),
do: 0
defp binary_powers("0" <> binary, position),
do: binary_powers(binary, position + 1)
defp binary_powers("1" <> binary, position),
do: (1 * 2 |> :math.pow(position) |> round()) + binary_powers(binary, position + 1)
end
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