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
···
On Sunday 11 July 2010, Adam Bourg wrote:
>I wrote a basic script that asks for your age then converts it into
>months, days and weeks old. I wanted to add some sort of control so that
>it would return an error if you didn't enter a number but rather a word
>or a letter or something.
>
>Can you please give me pointers? I've done quite a bit of Googling and
>am not sure how to do this. When I enter a number or a letter it
>returns the else statement. Please help! See attached for example of it
>being run.
>
>Here's my script below:
>
># Basic Program to ask for a persons age and out put that in months
># Writen by Adam Bourg on 2010-07-11
>
># Define verables
>months = 12
>
># Question that asks for your age
>puts "Hello, in the field below please enter your age:"
>
># Get's is the ruby method that asks for your age, it gets the
>information from # the terminal when you type
>age = gets
>
># This checks to see if you input a number, if you do it outputs the
>results
># if you don't it asks you for it in a numerical format eg 21
>if ( age.to_f.to_s == true )
> monthsold = age.to_i * months.to_i
> puts 'You are ' + monthsold.to_s + ' months old'
>else
> puts 'Error, please enter a number!'
> end
>
