# Lesson 4

# In this lesson, you will learn to use
# some basic arithmetic operators, code
# blocks, and iterators.

# General Instructions:
#
# This lesson contains four examples and three
# exercises (A, B, C).
#
# To listen to an example, change "comment"
# to "uncomment" on the "comment do" line,
# then click the "Run" menu command at the
# top of the Sonic Pi editor window.
# When you are done with the example, turn
# it off by changing "uncomment" back to
# "comment," and move on to the next section
# of the lesson.
#

# Operators: +, -, *, /
# Code Blocks: Do - End
# Iterators: ___.times Do

# Arithmetic Operators: In Lesson 3, we changed
# rhythmic values using the arithmetic operators
# * and / (multiply and divide). The operators
# + and - (add and subtract) can also be useful.

#  Example 1: + (add), - (subtract) operators

comment do
  play 60 + 2     # Play note 62
  sleep 1 + 1     # Sleep for 2 beats
  play :C4 + 2     # Play note 62
  sleep 1.0 - 0.5 # Sleep for half of a beat
  play :D4 - 2    # Play note :C4 (note 60)
end

# Exercise A: + and - operators.
#   Change the code in Example 1:
#   1) First three lines: change each + to -, and
#      change the second term in each so that the
#      result is the same as:
#
#         play 54
#         sleep 0.5
#         play :A3
#
#   2) Last two lines: change each - to +, and
#      change the second term in each so that the
#      result is the same as:
#
#         sleep 2
#         play :F4



# Blocks. A block of code is simply a group of \
# lines of code framed by ____ do ...end commands.
# Blocks are useful for organizing code into
# efficient chunks that are easier to follow and
# understand, and they often make it possible to
# less code (more efficient) than code without
# blocks. For example, using a "comment do" +
# "end" or "uncomment do" + "end" block to prevent
# or allow lines of code within the block to
# execute is simpler and more efficient than
# adding or removing "#" symbols for every
# line of code.

# Example 2: The comment block:
comment do
  play :C
  sleep 1
  play :D
  sleep 1
end

# Exercise B:
#     1) Add a # symbol to the beginning of the
#       "comment do" and the "end" lines in
#       Example 2, then Run.
#     2) Add "#" symbols to the beginning of each
#       line of code within the comment do ... end
#       block of Example 2, then Run.

# Notice how much more work this is than using
# the comment / uncomment toggles for the block.


# Iteration. An interesting and common way to use
# blocks is to repeat lines of code a certain
# number of times to achieve a result (iteration).
# You can use a repeating block of code to create
# a musical loop. In later lessons we will learn
# how to create variations within a repeating
# block.

# Example 3 - Block Iteration (repeating code)

comment do
  use_bpm 120
  4.times do
    play :C
    sleep 1
    play :C
    sleep 1
    play :G
    sleep 1
    play :G
    sleep 1
    play :A
    sleep 1
    play :A
    sleep 1
    play :G
    sleep 2
  end
end

# Exercise B - modify Example 3 so that the
# block of code is repeated 3 times instead
# of 4. For this exercise, copy and paste
# or re-type the code below. Leave the
# original Example 3 code unchanged so that
# you can use it again in Exercise C.




# Example 4 - Nested repeating code blocks.
# You can repeat code blocks within other
# code blocks:

comment do
  4.times do
    play :G
    sleep 1
    2.times do
      play :C
      sleep 1
    end
  end
end

# Exercise C - Example 3 contains repetitions
# of lines of code:
#   play :C sleep 1 (twice)
#   play :G sleep 1 (twice)
#   play :A sleep 1 (twice)
#
# Using repeating blocks, rewrite these lines
# so that they are repeated the correct number
# of times within the larger block, but are
# only written once in the code. Change the
# outer block so that it repeats twice rather
# than four times.