Ruby字符串不能被强制转换为Fixnum

Question

我正在尝试创建一个用于从学生记录中计算GPA的程序。输入学生的姓氏和名字后，我得到这些错误：

Please provide the last name of the desired student: 
Cirello 
Please provide the first name of the desired student: 
Brian 
proj3.rb:55:in `+': String can't be coerced into Fixnum (TypeError) 
     from proj3.rb:55:in `block in <main>' 
     from proj3.rb:53:in `each' 
     from proj3.rb:53:in `<main>' 

请帮我解决这个问题。这里是我的代码：

stud_id = [] 
last_name = [] 
first_name = [] 
course_number = [] 
course_name = [] 
prof_name = [] 
credit_hours = [] 
grade = [] 

grade_values = {       
    "A" => 4,      
    "B" => 3, 
    "C" => 2, 
    "D" => 1, 
    "F" => 0 } 

fin = File.open("student-records.txt", "r") 

while line = fin.gets 
    fields = line.chomp.split(',') 
    stud_id << fields[0] 
    last_name << fields[1] 
    first_name << fields[2] 
    course_number << fields[3] 
    course_name << fields[4] 
    prof_name << fields[5] 
    credit_hours << fields[6] 
    grade << fields[7] 
end 

fin.close 

puts "Please provide the last name of the desired student:" 
    desired_last_name = gets.chomp 
puts "Please provide the first name of the desired student:" 
    desired_first_name = gets.chomp 

desired_student_credit_hours = 0 
desired_student_grades = 0 
desired_student_indexes = [7] 
if last_name.include?(desired_last_name) && first_name.include?(desired_first_name) 
    last_name.each do |student_last_name, i| 
     if student_last_name == desired_last_name 
      desired_student_indexes << i 
     end 
    end 
end 
desired_student_indexes.each do |desired_student_index| 
    desired_student_grades += grade_values[grade[desired_student_index]] 
    desired_student_credit_hours += credit_hours[desired_student_index] 
end 
final_gpa = desired_student_grades/desired_student_credit_hours 
puts "This student's final GPA is: #{final_gpa}" 

Answer 1

请检查to_i方法将字符串转换为整数。你需要把它添加到两个grade_values[grade[desired_student_index]]和credit_hours[desired_student_index]像这样：

desired_student_grades += grade_values[grade[desired_student_index]].to_i 
desired_student_credit_hours += credit_hours[desired_student_index].to_i