No Method Error - Ruby Calculator

问题

Based on the Ruby Monk Calculator exercise, I was trying to build a simple calculator that can add and subtract:

class Calculator  
 def add(a,b)
   a + b 
 end

 def subtract(a,b)
   a - b 
 end
end

puts "input first integer"
a = gets.chomp.to_i

puts "input second integer"
b = gets.chomp.to_i

puts "add or subtract?"
response = gets.chomp.downcase

if response == "add" 
  Calculator.add(a,b)
else response == "subtract"
  Calculator.subtract(a,b)
end

When I run the code, I keep getting the 'NoMethodError' - the methods 'add' and 'subtract' are undefined. I don't understand why I'm getting this error, and wondering if I'm calling the method wrong.

回答1:

You defined your methods at the instance level, rather than the class level. Either use

def self.add(a,b)
  a + b 
end

or create an instance of Calculator

calc = Calculator.new
calc.add(a,b)

来源：https://stackoverflow.com/questions/31331287/no-method-error-ruby-calculator