Is there a way to 'cd ..' up a nested "if" statement tree? - ruby

I'm curious if there's a way to have the program go back up the if statement stack?
Ideally, the program would return to line 2 and prompt the user for the input variable, then continue to evaluate like it did the first time. Think of it like a cursor in a text editor, I just want to move it from either of those two comments back up to line 2. The two places of interest are commented out below:
while true
input = gets.chomp
if input != input.upcase
puts "HUH?! SPEAK UP, SONNY!"
elsif input == 'BYE'
puts "HUH?! SPEAK UP, SONNY!"
input = gets.chomp
if input == 'BYE'
puts "HUH?! SPEAK UP, SONNY!"
input = gets.chomp
if input == 'BYE'
puts "GOOD BYE!";
break
else
# return to top-level if statement
end
else
# return to top-level if statement
end
else
random_year = rand(1930..1950)
puts "NO, NOT SINCE #{random_year}!"
end
end

In the code you show, you don't need to do anything to make the flow of execution go back to line 2. Just omit the else clauses in the two places you marked. The flow of execution will drop down to the bottom of the while loop, then loop back to the top, then go back to line 2.

You need to use a while statement to set a condition flag and check it, which will loop back to the while statement if you don't change the flag:
flag = 0
while flag1 == 0
if var = "string"
then ...statements...
flag1 = 1 ; this allows us to break out of this while loop
else ...statements...
end
end
If flag1 is not 0 at the end of the while statement, the while statement will loop back. For two such conditions, you need to nest the while loops. You might have to re-order your statements to make multiple while loops work this way.

You can avoid this level of neasted ifs with:
byecount = 0
while byecount < 3
input = gets.chomp
if input == "BYE"
byecount += 1
next
else
byecount = 0
end
if input != input.upcase
puts "HUH?! SPEAK UP, SONNY!"
else
puts "NO, NOT SINCE #{rand(1930..1950)}!"
end
end
puts "GOOD BYE!"
Or you can write a catch..throw flow structure. (Really.. if you need to use it, something is wrong with your design)
catch :exitloop do
while ...
if ...
if ...
if ...
throw :exitloop
end
end
end
end
end

Here's how I'd write a similar exercise:
BYE = 'BYE'
HUH = "HUH?! SPEAK UP, SONNY!"
loop do
input = gets.chomp
if input != input.upcase
puts HUH
next
end
if input != BYE
random_year = rand(1930..1950)
puts "NO, NOT SINCE #{random_year}!"
next
end
puts HUH
input = gets.chomp
if input == BYE
puts HUH
input = gets.chomp
if input == BYE
puts "GOOD BYE!";
break
end
end
end
I used loop instead of while. Matz, the main man for Ruby, recommends loop. See "Is there a “do … while” loop in Ruby?" for further discussion about it.

Related

Ruby Endless Loop

I am new to Ruby. I have written the code below, its working about 90% except the else statement. The else statement triggers endless loop. I just want it to ask user to try again. Here is my code
puts "Do you want to print something? (Y / N)"
user = gets.chomp.downcase
answer = true
while answer
if user == "y"
puts "Something"
answer = false
elsif user == "n"
puts " "
answer = false
else
puts "Invalid input! Please enter Y or N"
end
end
Somewhat shorter (note user has gone, the answer is now referred to as answer).
answer = ""
until (answer == "y") or (answer == "n")
puts 'Do you want to print something? (Y/N)'
answer = gets.chomp.downcase
end
Once you exit the else, answer is still true. If you want to re-prompt, you can move your puts and user statement into the loop.
Something like this should work.
while true # (alternately) loop do
puts 'Do you want to print something? (Y/N)'
case gets.chomp.downcase
when 'y'
puts 'foo'
break
when 'n'
puts 'bar'
break
else
puts 'Invalid input! Please enter Y or N'
end
end
You can use break to exit out of your loop instead of setting up another variable. Also, this looks like a good use-case for a case statement to have some explicit cases listed.

How to jump to a line in ruby

I'm doing a pwd generator in ruby and when I get to a certain point of the code I need to return back if the user says that he want to retry to generate the pwd.
print "do you want to retry to generate the password? [y/n]"
retrypwd = gets.chomp
if retrypwd == y
(code to jump to some lines ago)
elsif retrypwd == n
print "Ok, It'll be for the next time"
end
The trick is to use a loop and break it or repeat it according to your expectations:
def try_again?
loop do
print "Would you like to try again? Y/N"
again = gets.chomp.capitalize
case (again)
when 'N'
return false
when 'Y'
return true
else
puts "Huh? I don't know what that means."
end
end
end
Then you can incorporate this into your main program:
begin
try_password
end while try_again?
You will keep trying passwords until try_again? returns false, which happens if you type "N".

How do I return an error message when the user inputs wrong info?

I have a program that displays a numbered list and asks the user to input either a number or name from the list, and loops a block until the user enters "exit", after which it ends.
I want to add a line or two that puts an error message like, "Sorry, I don't seem to understand your request" if the user inputs something that is not on the list (name/number) and is not the word "exit".
I can't seem to figure it out. Any advice? My current code is below.
def start
display_books
input = nil
while input != "exit"
puts ""
puts "What book would you more information on, by name or number?"
puts ""
puts "Enter list to see the books again."
puts "Enter exit to end the program."
puts ""
input = gets.strip
if input == "list"
display_books
elsif input.to_i == 0
if book = Book.find_by_name(input)
book_info(book)
end
elsif input.to_i > 0
if book = Book.find(input.to_i)
book_info(book)
end
end
end
puts "Goodbye!!!"
end
Seems that you should add an elsif statement in this if:
if book = Book.find_by_name(input)
book_info(book)
elsif input != 'exit'
puts "Sorry, I don't seem to understand your request"
end
A good template for an interpreter is to build around Ruby's very capable case statement:
loop do
case (gets.chomp.downcase)
when 'list'
display_books
when /\Afind\s+(\d+)/
if book = Book.find($1.to_i)
book_info(book)
end
when /\Afind\s+(.*)/
if book = Book.find_by_name($1)
book_info(book)
end
when 'exit'
break
else
puts "Not sure what you're saying."
end
end
Although this involves regular expressions, which can be a bit scary, it does give you a lot of flexibility. \A represents "beginning of string" as an anchor, and \s+ means "one or more spaces". This means you can type in find 99 and it will still work.
You can create a whole command-line interface with it if you take the time to specify the commands clearly. Things like show book 17 and delete book 17 are all possible with a bit of tinkering.

Begin rescue retry error

If this code executes the else statement, I want it to retry either from rescue or from begin.
Running the code asks me for an input and, when I input it, the code doesn't work.
1- What can I do to make this code work with the else statement running the retry?
2- Why does removing rescue create a retry Syntax Error?
# Creates input method
def input
x = gets.to_i
end
#Begins the first choice
begin
puts "What will you do?
1- Get a closer look
2- Go in the opposite direction
Write your input an press enter:"
rescue
#Calls input method
choice = input
if choice == 1
puts "You get a closer look and..."
elsif choice == 2
puts "You go in the opposite direction, out of trouble"
else
puts "Incorrect input, enter a number between the one's avaliables:"
end
#Retries if the choice is error
retry if choice != 1||2
end
Using a rescue block is for handling exceptions, I really don't think it's needed here. A loop will do the job.
puts "What will you do?",
"1- Get a closer look",
"2- Go in the opposite direction",
"Write your input and press enter:"
loop do
choice = gets.to_i
if choice == 1
puts "You get a closer look and..."
break
elsif choice == 2
puts "You go in the opposite direction, out of trouble"
break
else
puts "Incorrect input, enter a number between the ones available:"
end
end

gets.chomp three times in a row to exit

The task is taken from "Learn to Program" by Chrise Pine. The program is called 'Deaf Grandma'. Here's the task: "whatever you type, grandma (the program) should respond with this:
`HUH?! SPEAK UP, SONNY!`
unless you shout it (type in all capitals). In this case she responds with:
`NO, NOT SINCE 1938!`
Have Grandma shout a different year each time, maybe any year at random between 1930 and 1950. You have to shout BYE three times in a row. Make sure to test your program: if you shout
BYE three times but not in a row, you should still be talking to
Grandma."
Now, everything looks fine to me, except I didn't get where to put gets.chomp 3 times to exit a program. Eventually, I came up with this:
speak = gets.chomp
while speak != 'BYE'
puts 'HUH?! SPEAK UP, SONNY!'
if speak == speak.upcase
puts 'NO, NOT SINCE ' + (1930 + rand(20)).to_s + '!'
else repeat = gets.chomp
end
end
But in this case if I type BYE grandma still asks me:
`HUH?! SPEAK UP, SONNY!`
My question is: how can I properly make the program exit after I type BYE three times in a row?
Have a look at this, I've made some changes though. But should give you the expected output.
bye_count = 0
while true
speak = gets.chomp
if speak == 'BYE'
bye_count +=1
bye_count == 3 ? break : next
end
bye_count = 0 # Resets count
if speak == speak.upcase
puts 'NO, NOT SINCE ' + (1930 + rand(20)).to_s + '!'
else
puts 'HUH?! SPEAK UP, SONNY!'
end
end
You've not added anywhere in your code that using 'bye' 3 times will exit the program.
while bye < 3
Try looking at your code again and implementing the changes to exit after 3 byes.
Here's another way:
responses = ["", "", ""]
loop do
speak = gets.chomp
responses.shift
responses << speak
break if responses.all? { |r| r == "BYE" }
if speak == speak.upcase
puts 'NO, NOT SINCE ' + (1930 + rand(20)).to_s + '!'
else
puts 'HUH?! SPEAK UP, SONNY!'
end
end
Alternatively,
break if responses.uniq == ["BYE"]
puts "what can i do for your son?"
a=0
while a != 3
n= gets.chomp
if n.include? 'BYE'
puts "NO NOT SINCE #{rand(1897..1930)}".chomp
a = (a + 1)
end
if n != n.upcase
puts 'HUH?! SPEAK UP, SONNY!'.chomp
a=0
end
if n == n.upcase and n != 'BYE'
puts "NO NOT SINCE #{rand(1897..1930)}".chomp
a=0
end
end

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