How to get random 0 and 1 numbers

Question

So basically for fun I was trying to generate a column of numbers (7 digits only 0s and 1s) My code's pretty short:

a = rand(0000000-1111111)
b = 220
a1 = rand(0000000-1111111)
a2 = rand(0000000-1111111)
a3 = rand(0000000-1111111)
a4 = rand(0000000-1111111)
a5 = rand(0000000-1111111)

while b !=0
  puts a
  puts a2
  puts a3
  puts a4
  puts a5
end

My problem is that instead of generating a random column of 0s and 1s all the numbers are used.

Answer 1

Here's idiomaticish Ruby:

5.times do
  puts (1..7).map { [0, 1].sample }.join
end

Let's unpack it:

5.times do...end is pretty self-explanatory. Do whatever's between do and end five times.

(1..7) generates an array with seven elements. We don't actually care what's in it right now. map returns a new array where each element is the result of calling what's between the braces. So seven times we'll call [0, 1].sample and squeeze the results into an array. The sample itself, of course, randomly picks either 0 or 1. Finally .join turns an array into a string. If we'd said .join('-'), for example, it'd put a hyphen between each element (1-0-0-1-1-1-0-1). But since we didn't specify anything it puts nothing between each element (10011101).

And there you have it.

As others have noted, for this particular problem it's possible to do faster and shorter things by using binary. I don't think this is the Ruby Way though. With respect to speed, "premature optimization is the root of all evil", and if you have a violent aversion to slow code you shouldn't be coding Ruby anyway. With regards to readability, that way may be shorter, but the above way is a lot clearer. "Oh, we're doing something five times, and that's going to be printing out a 7-thing long...random sequence of 0s and 1s...as a string". It almost reads like English (if you know the word map (definition three)).

Answer 2

The best way to solve this is probably to do base conversion:

someNumber = rand(1 << 7) # Seven digits, max; 1 << 7 is 10000000 in binary.

puts someNumber.to_s(2).ljust(7, '0') # 10110100, e.g.

Answer 3

Derivation of @minitech's answer

 5.times { puts "%07b" % rand(128) }