CS 145 Lecture 27 – Array Exercises
Agenda
- what ?s
- array bingo
- making digital music
TODO
- Read chapter 7 through section 7.2. Write down 2-3 questions, observations, and sightings of arrays in real life on a 1/4 sheet turned in at the beginning of next lecture.
Note
In case you haven’t noticed yet, we don’t just jump from new topic to new topic in this class. We savor each one by exploring problems relevant to the current topic. Today, we see more of arrays in two ways. First we play some array bingo. Then we generate some music.
Bingo
The rules:
- Draft a board: an array of 10
ints. Each element is in [0, 9]. - The instructor calls out a series of boolean expressions about elements of a 10-
intarray. The leftmost element identified in the expression is the target. If the expression is true for the target element of your array, cross it off. - Occasionally the subscript of the target element will be expressed in terms of
i. On such occasions,ican take on any value in [0, 9], and multiple target elements may be crossed off. - The first player(s) to cross off all 10 elements wins.
1: board[0] == 3 2: board[4] % 2 == 1 3: board[9] > 5 4: board[i] == board[i - 1] 5: board[3] < 2 * board[5] 6: board[7] == board[6] + 1 7: board[i] == 0 8: board[2] < 7 9: board[board[3]] < 6 10: board[6] > board[1] + board[2] 11: board[5] >= board[0] && board[5] <= board[1] 12: board[board[i]] = i 13: board[8] % 3 == 2 14: board[1] < 10 15: board[i] == board[9 - i] 16: board[4] > board[9 / 2] 17: board[7] == board[0] || board[7] == board[1] || board[7] == board[2] || board[7] == board[3] 18: board[d6 roll] < d12 roll 19: board[i / 2] <= 4 20: board[i % 3] >= 7 21: board[5] > 100 % 3 22: board[6] < board[8] - board[7] 23: board[i] > board[i + 1] + 1 24: board[i % 4 + 3] >= 2 25: board[7] < board[5] - board[9] 26: board[4] != board[1] 27: board[d6 roll] > d6 roll
Music
Next we generate audio clips by sampling sine waves of various frequencies. The pressure at time t of a sound wave of a given frequency on our ear is sin(2 * pi * frequency * t). We’ll walk along regular intervals of time, store the pressure in an array, write the array out to disk, and play it through the sox utility with something like this:
play --endian big -c 1 -e float -r 22050 -b 32 samples.raw
To write out data, we’ll use a DataOutputStream. This class can write binary data. Instead of writing the float 1.23456 as seven chars, it writes the raw 4-byte representation. This keeps files smaller, but makes them not human readable.
Code
Sounder.java
/usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:315:in `to_specs': Could not find 'coderay' (>= 0) among 94 total gem(s) (Gem::MissingSpecError) Checked in 'GEM_PATH=/var/www/.local/share/gem/ruby/3.2.0:/var/lib/gems/3.2.0:/usr/local/lib/ruby/gems/3.2.0:/usr/lib/ruby/gems/3.2.0:/usr/lib/x86_64-linux-gnu/ruby/gems/3.2.0:/usr/share/rubygems-integration/3.2.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/3.2.0:/home/johnch/.gems' , execute `gem env` for more information from /usr/lib/ruby/vendor_ruby/rubygems/dependency.rb:327:in `to_spec' from /usr/lib/ruby/vendor_ruby/rubygems/core_ext/kernel_gem.rb:57:in `gem' from ./coderay:24:in `'
Haiku
Dear Santa lastnamePlease bring lots of boxed numbersi has been real good