grade_calc_ported_from_java.rb

class GradeCalc
  def initialize
    @@total_grade ||= 0.0
    @@total_percent_given ||= 0
    @assingment_num = nil
    @percent_of_total = nil
    @sum = 0
    @avg = 0
  end

  def add_assignments(percent_of_total, assignment_num)
    @percent_of_total     = percent_of_total
    @assignment_num       = assignment_num
    @@total_percent_given += @percent_of_total
  end

  def calc_grade_section(grades_input)
    @sum += grades_input.reduce(:+)
    @avg = @sum / @assignment_num

    @@total_grade += (@avg * @percent_of_total)
  end

  def calc_needed_grade
    grades_return = []

    if @@total_percent_given < 100
      {"A+" => 100, "A" => 90, "B" => 80, "C" => 70}.each do |k,v|
        needed = needed_grade(v)
        grades_return << k << (needed <= 0 ? "You don't need to finish this last section to make an #{k}" : needed.to_s)
      end
    else
      grades_return << "You have completed 100% of the class"
    end

    grades_return
  end

  def get_final_grade
    (@@total_grade * 100.0).round / 100.0
  end

  def get_avg
    @avg
  end

  def get_percent_of_total
    @percent_of_total
  end

  def get_sum
    @sum
  end

  def get_total_percent_given
    @@total_percent_given
  end

  private

  def needed_grade(grade_minimum)
    (((grade_minimum - @@total_grade) / grade_percent_needed) * 100).round / 100.0
  end

  def grade_percent_needed
    1 - @@total_percent_given
  end

end

sample.rb

require './grade_calc_ported_from_java'

hw = GradeCalc.new
hw.add_assignments(0.2, 10)
puts hw.calc_grade_section([100.0, 100.0, 80.0, 90.0, 100.0, 85.0, 100.0, 95.0, 70.0, 93.0])

labs = GradeCalc.new
labs.add_assignments(0.4, 8)
puts labs.calc_grade_section([100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 94.0])

tests = GradeCalc.new
tests.add_assignments(0.2, 3)
puts tests.calc_grade_section([107.0, 108.5, 106.0])

puts tests.get_final_grade

tests.calc_needed_grade.each do |grade|
  puts grade
end

slightly_ more_idiomatic_grade_calc.rb

class GradeCalc

  def initialize
    @total_grade = 0.0
    @total_percent_given = 0
  end

  def add_assignments(percent_of_total, grades)
    avg = grades.reduce(:+) / grades.length

    @total_grade += (avg * percent_of_total)
    @total_percent_given += percent_of_total
  end

  def calc_needed_grade
    grades_return = []

    if @total_percent_given < 100
      {"A+" => 100, "A" => 90, "B" => 80, "C" => 70}.each do |k,v|
        needed = needed_grade(v)
        grades_return << k << (needed <= 0 ? "You don't need to finish this last section to make an #{k}" : needed.to_s)
      end
    else
      grades_return << "You have completed 100% of the class"
    end

    grades_return
  end

  def get_final_grade
    (@total_grade * 100.0).round / 100.0
  end

  private

  def needed_grade(grade_minimum)
    (((grade_minimum - @total_grade) / grade_percent_needed) * 100).round / 100.0
  end

  def grade_percent_needed
    1 - @total_percent_given
  end

end

gc = GradeCalc.new
gc.add_assignments(0.2, [100.0, 100.0, 80.0, 90.0, 100.0, 85.0, 100.0, 95.0, 70.0, 93.0])

gc.add_assignments(0.4, [100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 94.0])

gc.add_assignments(0.2, [107.0, 108.5, 106.0])

puts gc.get_final_grade

gc.calc_needed_grade.each do |g|
  puts g
end