How to solve ruby string [closed] - ruby

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I'm new to ruby, and I'm trying to make a simple calculator in which a user types in a simple problem (such as addition or subtraction) and the answer is returned. The problem is when the user types in a question, the question itself is being returned instead of the answer to that question.
puts "How many Questions?"
questions = gets.chomp.to_i
questions.times do |problem|
puts "question: "
problem = gets.chomp
puts "answer: #{problem}"
end

Answer 1

Inside your loop, instead of:
problem = gets.chomp
puts "answer: #{problem}"
Try this:
problem = gets.chomp
solved_problem = eval(problem)
puts "answer : #{solved_problem}"
eval will take care of interpreting your string as a Ruby instruction. But it's very messy, because anyone could write any Ruby program in your input and eval will make it run, so it's not safe at all.
If you only want to take care of simple operations, you can use a regex first to check if the input string looks like what you want:
problem_is_ok = (problem =~ /^\d+ *[+-] *\d+$/)
This will be true if the string starts with a number, followed by 0 to many spaces, followed by either a + or - sign, followed by 0 or more spaces, followed by another number and nothing else. Then you raise an error if this is not true.
Your loop now look like this:
questions.times do |problem|
puts "question: "
problem = gets.chomp
problem_is_ok = (problem =~ /^\d+ *[+-] *\d+$/)
if problem_is_ok
puts "answer: #{eval(problem)}"
else
#I raise an error, but you might aswell just print it instead for your simple program
raise ArgumentError("Can't compute this")
end
end

Answer 2

Add and subtract can be simple ruby definitions
We pass in 5 and 1
The lower portion of the code is the clear user interface implementation
when we loop we do it 3 times
It outputs 3 options for the user to select from
We read in with chomp, standard in, the keyboard, chooses 1, 2, or 3
If elsif statements conditionally select for each case
Using string interpolation we render the variables a and b into a new string,
and run their respective methods (add or subtract)
Converting that methods integer output to a string, and concatenate it.
Outputting that to the users screen
The 3rd option does no calculation,
instead it prints to users screen a simple string
our else condition catches the case when people don't enter one of the choices of 1, 2 or 3
It tells you to correct your choice to the options provided
Hope this helps
#!/usr/bin/env ruby
questions = 3
a, b = 5, 1
def add(a,b)
a + b
end
def subtract(a,b)
a - b
end
questions.times do |questions|
puts "Please choose:
1. add
2. subtract
3. exit"
questions = gets.chomp
if questions == '1'
puts "#{a} + #{b} = " + add(a,b).to_s
elsif questions == '2'
puts "#{a} - #{b} = " + subtract(a,b).to_s
elsif questions == '3'
puts 'exiting, goodbye.'
exit
else
p 'please choose again'
end
end