On Sunday 11 July 2010, Adam B. wrote:
|Here’s my script below:
|# Get’s is the ruby method that asks for your age, it gets the
| puts ‘Error, please enter a number!’
| end
|
There are a couple of errors in your code. First of all, in ruby you
never
compare something with true (or false) in an if. That’s because the only
value
which is == to true is… true (and the only value which is == to false
is
false). This explains why you keep getting the error message: you’re
comparing
the string returned by the to_s method with true. These are different,
so the
== operator returns false, which leads to executing the “else” branch of
the
if.
The if statement in ruby works in the following way: it checks what
value the
condition evaluates to. If it’s the false object or the nil object,
then
the “else” branch is executed. All other values cause the “if” branch to
be
executed. So, to test whether a condition is true, you simply write:
if some_expression
…
else
…
end
where some_expression is any piece of ruby code which doesn’t evaluate
to
false or nil.
The first step to fix your code, then, is to remove everything left to
the
to_s inside the condition. You can also remove the brackets, as they’re
not
needed around the condition in an if statement.
This leaves us with:
if age.to_f.to_s
Now, the to_s method of any object will return a string which ruby will
always
consider a true value. This means that now we have the opposite problem
we had
before: the error message is never shown. Removing the to_s would help
if
String#to_f didn’t return 0.0 (which is also considered a true value) in
case
the string doesn’t represent a number.
The simplest way to tell whether a string represents a number is to use
the
Kernel#Float method, or Kernel#Integer if you want an integer number.
Unlike
String#to_f and String#to_i, which always return a number, these methods
raise
an exception if the string can’t be translated to a number. So you can
write:
#gets returns the string with a trailing newline, so you have to remove
it
age = gets.strip
age_numeric = begin Integer(age)
rescue ArgumentError
puts “Enter a valid number”
exit
end
#months is already an integer, so there’s no need to call to_i on it
monthsold = age_numeric * months
I hope this helps
Stefano
