account.rb：17：in`withdraw'：未定義的方法` - '爲零：NilClass（NoMethodErro r）

Question

我在執行窗體終端時出錯。

withdraw : undefined method '-' 

我不明白爲什麼。我曾嘗試用sublime和記事本++進行編輯。

class Account 
    def initialize(name, balance, phone_no) 
     @name = name 
     @balance = balance 
     @phone_no = phone_no 
    end 

    def deposit(amount) 
     @amount += amount 
    end 

    def withdraw(amount) 
     @amount -= amount 
    end 

    def display() 
     puts "Name: " + @name 
     puts "Phone number: " + @phone_no.to_s 
     puts "Balance: " + @balance.to_s 
    end 

    def transfer(amount, target_account) 
     @balance -= amount 
     target_account.deposit(amount) 
    end 

    def status 
     return @balance 
    end 
end 

Answer 1

這兩種方法不應該在@balance上運行嗎？

def deposit(amount) 
    @balance += amount 
end 

def withdraw(amount) 
    @balance -= amount 
end 

@amount是nil。你這樣做

@amount = nil - amount 

和nil沒有一個-方法

Answer 2

@amount是nil在deposit和withdraw方法。並且您不能在nil對象上調用-方法。可能你拼錯@balance爲@amount？

def deposit(amount) 
    @balance += amount 
end 

def withdraw(amount) 
    @balance -= amount 
end