teaching machines

CS 145 Lecture 26 – Birthdays

November 4, 2015 by Chris Johnson. Filed under cs145, fall 2015, lectures.

Agenda

• what ?s
• loop until fixed
• repeated birthdays

TODO

• For an extra credit participation point, check out tryruby.org and work through at least level 5. Write down 2-3 questions, observations, or comparisons to Java or other languages you know.

Note

Today we introduce an idiom we can use to support a “try again” when an exception happens. I call this the loop until fixed pattern:

isValid = false
while not isValid
  try
    attempt the dangerous
    isValid = true
  catch
    issue warning message
end

Let’s use this pattern as we attempt the problem we introduced last time: figuring out which of your birthdays repeat. I hope you realize in all our examples are the pieces of the solutions to many of the problems you will encounter. We teachers are always torn between teaching concepts in a decontextualized way or a contextualized way. I prefer contextualized, but the danger is that when we talk about ideas situated inside a particular example, you don’t carry the ideas out to other situations.

So, what do we need to do to find our repeated birthdays?

Code

Bepeats.java

/usr/lib/ruby/2.7.0/rubygems/dependency.rb:311:in `to_specs': Could not find 'coderay' (>= 0) among 56 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/.gem/ruby/2.7.0:/var/lib/gems/2.7.0:/usr/lib/ruby/gems/2.7.0:/usr/share/rubygems-integration/2.7.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.7.0:/home/johnch/.gems', execute `gem env` for more information
	from /usr/lib/ruby/2.7.0/rubygems/dependency.rb:323:in `to_spec'
	from /usr/lib/ruby/2.7.0/rubygems/core_ext/kernel_gem.rb:62:in `gem'
	from ./coderay:24:in `
'

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