Problem comprehending C-style ruby loops

Question

I find the .each do hard to get to stick, so I was hoping for regular use of C for loop syntax which seems to not work, so I tried a while but still get errors.

I have tried this.

i = 0
while i < SampleCount
    samples[i] = amplitude
    amplitude *= -1
    i++
end

I get complaints about the end statement here.

Answer 1

There are several problems with your code. Rather than just fixing the errors, I'd suggest it's better long-term for you to learn the Ruby way - it will save you time and energy later. In this case, it's

5.times do |i|
  samples[i] = amplitude  # assumes samples already exists and has 5 entries.
  amplitude *= -1
end

If you insist on keeping a similar style, you can do this:

samples = []
i = 0
while i < sample_count
    samples << amplitude  # add new item to array.
    amplitude *= -1
    i += 1                # you can't use ++.
end

Note that SampleCount's initial capital letter, by Ruby convention, means a constant, which I'm guessing isn't what you really mean.

Answer 2

You originally mentioned trying to use a for loop. Notwithstanding the various other comments in the answers, here's the for loop approach:

for i in 0...5
  samples[i] = amplitude
  amplitude *= -1
end

Answer 3

I agree with Peter that there are other (more idiomatic) ways to do this in Ruby, but just to be clear: the error message you saw misdirected you. There wasn't anything wrong with your while loop per se. The problem was i++ since there is no ++ operator in Ruby.

This would work just fine:

limit = 10

i = 0
while i < limit
    puts i
    i += 1
end

Again, I'm not recommending it, but if you're just learning the language, it may help to know where the problem really was.

Ruby has a lot of built-in ways to iterate other than for or while (which tend to be seen less often, as far as I can tell). A few other examples:

(1..10).each do |x| # 1..10 is a range which you can iterate over with each
  puts x
end

1.upto(10) { |x| puts x } # Integers have upto and downto methods that can be useful

Answer 4

Nobody here has actually offered an alternate solution that actually does what Fred originally intended - and that's iterate around the value of the constant SampleCount. So could you do:

SampleCount.times do |i|

Or:

limit = SampleCount
limit.times do |i|

Or:

for i in 0..SampleCount

Would any of those be Ruby-esque enough?

Answer 5

The problem with the end statement is related to i++. Ruby wants to add something. There is no increment operator in Ruby. You need to use i += 1. With that change you can use your C style loop as is.