How to Determine if a given User input is a Float, String, or a Integer in Ruby - rubymine

Question

The is_a? method doesn't work; I have tried it and it apparently it checks if the value is derived from an object or something.
I tried something like this:
printf "What is the Regular Price of the book that you are purchasing?"
regular_price=gets.chomp
if regular_price.to_i.to_s == regular_price
print "Thank You #{regular_price}"
break
else
print "Please enter your price as a number"
end
Can someone explain to me more what .to_i and .to_s do? I just thought they convert the user input to a string, or a Numerical Value. I actually don't know how to check input to see if what he put in was a float, a String, or a decimal.
I just keep getting Syntax errors. I just want to know how to check for any of the 3 values and handle them accordingly.

Answer 1

There's a lot to your question so I recommend that you read How do I ask a good question? to help you get answers in the future. I'll go through each of your questions and try to provide answers to point you in the right direction.
The is_a? method works by accepting a class as a parameter and returning boolean. For example:
'foo'.is_a?(String)
=> true
1234.is_a?(Integer)
=> true
'foo'.is_a?(Integer)
=> false
1234.is_a?(String)
=> false
1.234.is_a?(Float)
=> true
The .to_i method is defined on the String class and will convert a string to an Integer. If there is no valid integer at the start of the string then it will return 0. For example:
"12345".to_i #=> 12345
"99 red balloons".to_i #=> 99
"0a".to_i #=> 0
"hello".to_i #=> 0
The .to_s method on the Integer class will return the string representation of the Integer. For example:
1234.to_s
=> '1234'
The same is true of Float:
1.234.to_s
=> '1.234'
Now let's take a look at your code. When I run it I get SyntaxError: (eval):4: Can't escape from eval with break which is happening because break has nothing to break out of; it isn't used to break out of an if statement but is instead used to break out of a block. For example:
if true
break
end
raises an error. But this does not:
loop do
if true
break
end
end
The reason is that calling break says "break out of the enclosing block," which in this case is the loop do ... end block. In the previous example there was no block enclosing the if statement. You can find more detailed explanations of the behavior of break elsewhere on stackoverflow.
Your final question was "I just want to know how to check for any of the 3 values and handle them accordingly." This answer explains how to do that but the code example is written in a way that's hard to decipher, so I've rewritten it below in an expanded form to make it clear what's happening:
regular_price = gets.chomp
begin
puts Integer(regular_price)
rescue
begin
puts Float(regular_price)
rescue
puts 'please enter your price as an Integer or Float'
end
end
What this code does is first it attempts to convert the string regular_price to an Integer. This raises an exception if it can't be converted. For example:
Integer('1234')
=> 1234
Integer('1.234')
ArgumentError: invalid value for Integer(): "1.234"
Integer('foo')
ArgumentError: invalid value for Integer(): "foo"
If an exception is raised then the rescue line stops the exception from being raised and instead continues executing on the next line. In this case, we're saying "if you can't convert to Integer then rescue and try to convert to Float." This works the same way as converting to Integer:
Float('1.234')
=> 1.234
Float('foo')
ArgumentError: invalid value for Float(): "foo"
Finally, we say "if you can't convert to Float then rescue and show an error message."
I hope this helps and answers your questions.