am learning ruby and i had come across this particular issue.
I have method which reads the user input data into an array and i have another method which displays the values in the same array to the user with some processing.
However this doesnt seem to be the correct way as the system always throws a
Arraypass.rb:23:in <main>': undefined local variable or methodnames' for main:Object (NameError)
Appreciate if someone can show a way forward in this,
for example:
class School
def askdetails
print "How many students are there"
n=(gets.chomp.to_i - 1)
print "Enter names one by one"
names=Array.new(n)
for i in (0..n)
names[i]=gets.chomp
end
return names,n
end
def showdetails(names,n)
for i in (0..n)
puts names[i]
end
end
end
stud=School.new
stud.askdetails
stud.showdetails(names,n)
Write the code as
#!/usr/bin/env ruby
class School
def askdetails
print "How many students are there"
n = gets.chomp.to_i - 1
print "Enter names one by one"
names = Array.new(n)
for i in (0..n)
names[i]=gets.chomp
end
return names,n
end
def showdetails(names,n)
for i in (0..n)
puts names[i]
end
end
end
stud = School.new
names, n = stud.askdetails
stud.showdetails(names,n)
The thing, you missed is #askdetails methods returning an Array, which you didn't assign any where before using those.
Read Array Decomposition, this is what I did here :
names, n = stud.askdetails
here is your answer:
names,n = stud.askdetails
stud.showdetails(names,n)
Related
So I've been messing around with Ruby for the first time after finishing the codecademy course up to "Object Oriented Programming, Part I" and I decided to start making a calculator. For some reason though, I get this error:
calc.rb:13:in `addition': undefined local variable or method `user_input' for main:Object (NameError)
from calc.rb:21:in `<main>'
I'm confused why it doesn't see my "user_input" array. Is it out of the scope of the method? Did I initialize it wrong?
Here's the code so you can see for yourself, it's obviously nothing sophisticated and it's not finished. I'm just trying to test for addition right now.
#!/usr/bin/env ruby
user_input = Array.new
puts "Would you like to [a]dd, [s]ubtract, [m]ultiply, or [d]ivide? "
type_of_math = gets.chomp
def addition
operator = :+
puts "Please enter the numbers you want to add (enter \"=\" to stop adding numbers): "
until gets.chomp == "="
user_input << gets.chomp.to_i
end
sum = user_input.inject(operator)
return sum
end
case type_of_math
when "a"
addition
when "s"
puts "Test for subtraction"
when "m"
puts "Test for multiplication"
when "d"
puts "Test for division"
else
puts "Wrong"
end
Consider this untested variation on your code. It's more idiomatic:
def addition
user_input = []
puts 'Please enter the numbers you want to add (enter "=" to stop adding numbers): '
loop do
input = gets.chomp
break if input == '='
user_input << input
end
user_input.map(&:to_i).inject(:+)
end
Notice that it puts user_input into the method. It also uses the normal [] direct assignment of an empty array to initialize it. Rather than chomp.to_i each value as it's entered it waits to do that until after the loop exits.
Instead of while loops, consider using loop do. They tend to be more easily seen when scanning code.
Also notice there's no return at the end of the method. Ruby automatically returns the last value seen.
The below combined programs should ask for a number remove the first digit (lets call this new number x) and then compute x % 7. Ex: (1121546 % 7) = 5
This all appears to be working except that the number entered in will always compute to 0. modulo_7.rb works by itself and will print the correct outcome when passed a parameter.
The question is am I not passing the variables/ parameters properly or is there something else that is getting in the way?
class Number_check_interface
def get_cert_number
print "You are about to check receive the check number for a policy/cert id."
#cert_id = nil
until #cert_id.is_a?(Fixnum) do
puts " Enter the policy/cert ID. "
begin
#cert_id = Integer(gets)
rescue ArgumentError
end
end
end
end
class Run_number_check_interface
def run
load 'modulo_7.rb'
n = Number_check_interface.new
n.get_cert_number
checking_policy_number = Get_policy_check_digit.new(#cert_id)
checking_policy_number.create_check_digit
end
end
run = Run_number_check_interface.new
run.run
modulo_7.rb
This program removes the first digit (index 0) of a 7 digit number and returns the difference 7%18 is 4 since 4 is remainder of how many times 7 can fit into 18.
class Get_policy_check_digit
def initialize(cert_id)
#instance variable
#cert = cert_id
end
def create_check_digit
cert_id_6 = #cert.to_s
cert_id_6.slice!(0)
puts cert_id_6
check_digit = cert_id_6.to_i % 7
puts "Your check digit is #{check_digit}"
end
end
# n = Get_policy_check_digit.new(1121546) When uncommented this will create a new instance
# of Get_policy_check_digit with the parameter 1121546
# n.create_check_digit This will run the method create_check_digit with the
# parameter 1121546
Instance variables are scoped to an individual instance of a class. So when you say #cert_id = Integer(gets) inside Number_check_interface, you are only setting #cert_id for that particular instance of Number_check_interface. Then, when you later write Get_policy_check_digit.new(#cert_id) inside Run_number_check_interface, you are referring to an entirely different #cert_id, one which is specific to that particular instance of Run_number_check_interface, and not to the Number_check_interface you stored in n earlier.
The simple solution is to return #cert_id from Number_check_interface#get_cert_number, and then pass the returned value to Get_policy_check_digit.new:
class Number_check_interface
def get_cert_number
print "You are about to check receive the check number for a policy/cert id."
#cert_id = nil # This is an instance variable. It's only accessible
# from inside this instance of `Number_check_interface`
until #cert_id.is_a?(Fixnum) do
puts " Enter the policy/cert ID. "
begin
#cert_id = Integer(gets)
rescue ArgumentError
end
end
return #cert_id # Return the contents of #cert_id
end
end
class Run_number_check_interface
def run
load 'modulo_7.rb'
n = Number_check_interface.new
cert_number = n.get_cert_number # Here we call `get_cert_number` and
# set `cert_number` to it's return
# value.
# Notice how we use `cert_number` here:
checking_policy_number = Get_policy_check_digit.new(cert_number)
checking_policy_number.create_check_digit
end
end
Other tips:
Convention in Ruby is to name classes with CamelCase.
Require dependencies at the top of your files, not in the middle of method calls.
Unless you have a very good reason not to, use require, not load
You might want to think a bit harder about what purpose these classes serve, and what behavior they are intending to encapsulate. The API seems a bit awkward to me right now. Remember, tell, don't ask.
Why are these separate classes? The design here seems strange, is this ported from another language? It's more complicated than it needs to be. Without changing your structure, here's what's wrong:
In Run_number_check_interface you are reading #cert_id, it doesn't have an instance variable named that, but Number_check_interface does. Just return it from get_cert_number:
class Number_check_interface
def get_cert_number
print "You are about to check receive the check number for a policy/cert id."
cert_id = nil
until cert_id.is_a?(Fixnum) do
puts " Enter the policy/cert ID. "
begin
cert_id = Integer(gets)
rescue ArgumentError
end
end
cert_id # <-- returing the value here
end
end
class Run_number_check_interface
def run
load 'modulo_7.rb'
n = Number_check_interface.new
cert_id = n.get_cert_number # <-- saving here
checking_policy_number = Get_policy_check_digit.new(cert_id) # <-- no longer an ivar
checking_policy_number.create_check_digit
end
end
run = Run_number_check_interface.new
run.run
I'm working on Chris Pine's Ruby tutorial. I have to write a cheat method that allows me to set which side of the die I want to show: https://pine.fm/LearnToProgram/?Chapter=09
I have two instance variables: #numberShowing and #numberCheat. #numberCheat receives an input from the user and I want to set #numberShowing to take the value of #numberCheat. However, #numberShowing always outputs some random number. Any tips?
Here's my code so far:
class Die
def initialize
roll
end
def roll
#numberShowing = 1 + rand(6)
end
def showing
#numberShowing
end
def cheat
puts "cheat by selecting your die number between 1 and 6"
#numberCheat = gets.chomp
end
#numberShowing = #numberCheat
end
puts Die.new.cheat
puts Die.new.showing
Thanks!
Move #numberShowing = #numberCheat into the cheat method. But your test is not going to prove it worked. Try something like:
die = Die.new
puts "Currently showing #{die.showing}"
puts "Cheating to change showing number to #{die.cheat}"
I've been sifting through the prior questions and answers on stackoverflow, and I have gotten most of my question figured out. I figured out that I can't place a function call within a hash, without placing it within a proc, or a similar container.
What I'm ultimately trying to do is have a menu displayed, grab user input, and then iterate through the hash, and run the specified function:
def Main()
menu_titles = {"Answer1" => Proc.new{Choice1()}}
Menu(menu_titles)
end
def Choice1()
puts "Response answer"
end
def Menu(menu_titles)
menu_titles.each_with_index do |(key, value),index|
puts "#{index+1}. #{key}"
end
user_input = 0
menu_titles.each_with_index do |(key, value), index|
if index.eql?(user_input)
menu_titles[value]
break
end
end
end
Main()
The issue I'm having right now is that I'm not entering the functions that my hash calls for. Whether I use a return or a "puts", I either get a blank line or nothing at all. If anyone has other recommendations about my code, I'm all ears also. To be honest, I don't like using procs, but that's mostly because I don't entirely know how they work and where to use them.
Right now for my menus I have:
user_input = 1
if user_input == 1
Choice1()
...
end
Here's how I would refactor this:
class Menu
attr_reader :titles
# initialize sets up a hard-coded titles instance variable,
# but it could easily take an argument.
def initialize
#titles = {
"Answer1" => Proc.new{ puts "choice 1" },
"Answer2" => Proc.new{ puts "choice 2" }
}
end
# This is the only public instance method in your class,
# which should give some idea about what the class is for
# to whoever reads your code
def choose
proc_for_index(display_for_choice)
end
private
# returns the index of the proc.
def display_for_choice
titles.each_with_index { |(key,value), index| puts "#{index + 1}. #{key}" }
gets.chomp.to_i - 1 # gets will return the string value of user input (try it in IRB)
end
# first finds the key for the selected index, then
# performs the hash lookup.
def proc_for_index(index)
titles[titles.keys[index]]
end
end
If you're serious about Ruby (or object-oriented programming in general), I would highly recommend learning about the advantages of packaging your code into behavior-specific classes. This example allows you to do this:
menu = Menu.new
proc = menu.choose
#=> 1. Answer1
#=> 2. Answer2
2 #(user input)
proc.call
#=> choice 2
And you could actually run it on one line:
Menu.new.choose.call
In Ruby:
for i in A do
# some code
end
is the same as:
A.each do |i|
# some code
end
for is not a kernel method:
What exactly is "for" in ruby
Is there a way to use other keywords to do similar things?
Something like:
total = sum i in I {x[i]}
mapping to:
total = I.sum {|i] x[i]}
It's almost syntax sugar. One difference is that, while for would use the scope of the code around it, each creates a separate scope within its block. Compare the following:
for i in (1..3)
x = i
end
p x # => 3
versus
(1..3).each do |i|
x = i
end
p x # => undefined local variable or method `x' for main:Object
for is just syntax sugar for the each method. This can be seen by running this code:
for i in 1 do
end
This results in the error:
NoMethodError: undefined method `each' for 1:Fixnum
For is just syntactic sugar.
From the pickaxe:
For ... In
Earlier we said that the only built-in Ruby looping primitives were while and until. What's this ``for'' thing, then? Well, for is almost a lump of syntactic sugar. When you write
for aSong in songList
aSong.play
end
Ruby translates it into something like:
songList.each do |aSong|
aSong.play
end
The only difference between the for loop and the each form is the scope of local variables that are defined in the body. This is discussed on page 87.
You can use for to iterate over any object that responds to the method each, such as an Array or a Range.
for i in ['fee', 'fi', 'fo', 'fum']
print i, " "
end
for i in 1..3
print i, " "
end
for i in File.open("ordinal").find_all { |l| l =~ /d$/}
print i.chomp, " "
end
produces:
fee fi fo fum 1 2 3 second third
As long as your class defines a sensible each method, you can use a for loop to traverse it.
class Periods
def each
yield "Classical"
yield "Jazz"
yield "Rock"
end
end
periods = Periods.new
for genre in periods
print genre, " "
end
produces:
Classical Jazz Rock
Ruby doesn't have other keywords for list comprehensions (like the sum example you made above). for isn't a terribly popular keyword, and the method syntax ( arr.each {} ) is generally preferred.