Ruby If Else syntax evaluation

Question

I don't understand why my If else statement doesn't work properly, if I the input 'y' then it evaluates the last part of the if else statement.

puts('give 1: ')
nr1= Integer(gets)
puts('give 2: ')
nr2= Integer(gets)

selection = gets.to_s

if (selection == "y".upcase)
  puts "Result is #{nr1+nr2}"
elsif (selection =="v".upcase)
  puts "Result is #{nr1-nr2}"
else (selection == "k".upcase)
  puts "Result is #{nr1*nr2}"
end

else (selection == "k".upcase) will be treated as plain else. Probably you want elsif in place. — Radix
– Radix, Commented Jul 17, 2017 at 20:24
I did try switching it but it does not have any effect, it does not print the result if i input 'y' ,'v' or 'k'. — Orack Babama
– Orack Babama, Commented Jul 17, 2017 at 20:27
You want if selection.chomp.downcase == "y" (or if selection.chomp.upcase == "Y"). gets.to_s is the same as gets. gets always returns a string that ends with a newline ("\n"). You need gets.chomp to remove that newline. — Cary Swoveland
– Cary Swoveland, Commented Jul 17, 2017 at 20:32

tadman · Accepted Answer · 2017-07-17 20:37:03Z

4

A good habit to get into is breaking this out into a proper case statement:

case (selection.upcase)
when 'Y'
  puts "Result is #{nr1+nr2}"
when 'V'
  puts "Result is #{nr1-nr2}"
when 'K'
  puts "Result is #{nr1*nr2}"
else
  puts "I don't know what you mean."
end

Now it's important to note that selection == "y".upcase compares selection to "Y", it doesn't upcase your selection. I've adjusted that here do to a case-insensitive match on selection by using that as the thing the case is operating on.

answered Jul 17, 2017 at 20:37

tadman

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5 Comments

Orack Babama Over a year ago

Thank you, my problem was that I was inputting 'y' and the if statement was waiting for uppercase 'Y' which is why it did not execute.

tadman Over a year ago

Yeah, you almost had it, but things were a bit jumbled up. Hope this helped clarify.

tadman Over a year ago

@CarySwoveland A look-up table mapping string to operation and using send would be a better solution here, absolutely.

Cary Swoveland Over a year ago

Another option is to use a hash.

h = { 'Y'=>:+, 'V'=>:-, 'K'=>:* }; selection = gets.chomp.upcase; puts "Result is #{nr1.send(h[selection], nr2)}" if h.key?(selection)

.

tadman Over a year ago

@CarySwoveland You should probably add that as an alternate answer just for educational purposes.

Radix · Accepted Answer · 2018-07-24 20:53:22Z

1

You're missing #chomp method. As \n is appended to the STDIN which you can remove using #chomp.

2.2.2 :032 > selection = gets
y
 => "y\n"
2.2.2 :033 > selection.chomp
 => "y"

You can update your code as follows:

selection = gets.to_s.chomp.upcase

if selection == 'Y'
  puts "Result is #{nr1+nr2}"
elsif selection == 'V'
  puts "Result is #{nr1-nr2}"
elsif selection == 'K'
  puts "Result is #{nr1*nr2}"
else
  puts 'Invalid input'
end

Although, ruby case will suit best here. Something like:

case selection.upcase
when 'Y'
  puts "Result is #{nr1 + nr2}"
when 'V'
  puts "Result is #{nr1 - nr2}"
when 'K'
  puts "Result is #{nr1 * nr2}"
else
  puts "Invalid input. Please provide a valid input [Y/V/K]"
end

edited Jul 24, 2018 at 20:53

answered Jul 17, 2017 at 20:28

Radix

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3 Comments

Cary Swoveland Over a year ago

Can "y".upcase be simplified? Is that really what you want? Any why to_s in gets.to_s.chomp?

Radix Over a year ago

@CarySwoveland Yes, there's no need for #to_s. Updated the answer.

Mark Thomas Over a year ago

I'm pretty sure if selection.upcase == "Y" is what is intended here.

Cary Swoveland · Accepted Answer · 2017-07-18 00:10:23Z

0

One option is to use a hash.

h = { 'Y'=>:+, 'V'=>:-, 'K'=>:* }
selection = gets.chomp.upcase
puts "Result is #{nr1.public_send(h[selection], nr2)}" if h.key?(selection)

answered Jul 18, 2017 at 0:10

Cary Swoveland

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