tiny little script to calculate a gpa in ruby

calculate_gpa.rb

# a Hash of mappings between letter grade and GPA value
@grades = {                                               
    'a' => 4.0,                                           
    'b' => 3.0,                                           
    'c' => 2.0,                                           
    'd' => 1.0,                                           
    'f' => 0.0                                            
}                                                         

# a method for calculating a student's GPA                                                          
def calculate_gpa(student)                                
  total = 0                                               
  student.each do |grade|                                 
    total += @grades[grade]                               
  end                                                     
  total / student.size                                    
end