Can't get my regexp to work to test if numerical

ruby-talk
1

alright, this seems easy enough.

Building a Bank class, deposits must be floating, so if it has any
letters, it will tell the user it needs numbers

         if amount == /^[0-9]$/
         deposit_to_acct(amount,current_account)
         puts 'You have deposited ' + amount.to_s

          else
          puts 'Must be a number, alphabet bank is next door to your
right'

        end

it goes straight to the else statement, never executes the
deposit_to_acct method.

What part am I doing wrong?

···

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2

Feng Tien wrote:

alright, this seems easy enough.

Building a Bank class, deposits must be floating, so if it has any
letters, it will tell the user it needs numbers

         if amount == /^[0-9]$/
         deposit_to_acct(amount,current_account)
         puts 'You have deposited ' + amount.to_s

          else
          puts 'Must be a number, alphabet bank is next door to your
right'

        end

1) The pattern /^[0-9]$/ matches one digit.

2) amount would have to be a regex object to == the regex on the right.

if 'abc' == /abc/
  puts 'yes'
else
  puts 'no'
end

regex_obj = /abc/

if regex_obj == /abc/
  puts 'yes'
else
  puts 'no'
end

--output:--
no
yes

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3

I would say that you need a better understanding of regular expressions and how they are matched to strings in Ruby. The expression

    amount == /^[0-9]$/

is an equality test and will always be false if 'amount' is a string. Consider the following examples:

<code>
# the following perform equality tests, not string to regular expression matching
123 == /^[0-9]$/ # => false
'123' == /^[0-9]$/ # => false
/^[0-9]$/ == /^[0-9]$/ # => true
/^[0-9]$/.equal?(/^[0-9]$/ )# => false
# the following perform regular expression matching
'123' =~ /^[0-9]$/ # => nil (match fails because RE only accepts one digit)
'3' =~ /^[0-9]$/ # => 0 (match succeeds)
'123' =~ /^[0-9]+$/ # => 0 (match succeeds)
'123X' =~ /^[0-9]+$/ # => nil (match fails)
</code>

Regards, Morton

···

On Nov 2, 2007, at 12:47 AM, Feng Tien wrote:

Building a Bank class, deposits must be floating, so if it has any
letters, it will tell the user it needs numbers

         if amount == /^[0-9]$/
         deposit_to_acct(amount,current_account)
         puts 'You have deposited ' + amount.to_s

          else
          puts 'Must be a number, alphabet bank is next door to your
right'

        end

it goes straight to the else statement, never executes the
deposit_to_acct method.

What part am I doing wrong?

4

7stud -- wrote:

Feng Tien wrote:

alright, this seems easy enough.

Building a Bank class, deposits must be floating, so if it has any
letters, it will tell the user it needs numbers

         if amount == /^[0-9]$/
         deposit_to_acct(amount,current_account)
         puts 'You have deposited ' + amount.to_s

          else
          puts 'Must be a number, alphabet bank is next door to your
right'

        end

1) The pattern /^[0-9]$/ matches one digit.

That's incorrect. The pattern matches: the start of the line, followed
by one digit, followed by the end of the line. So the regex won't
match a digit in a line containing two digits:

regex = /^[0-9]$/

line = '8'
match_obj = regex.match(line)
p match_obj.to_a

line = '12'
match_obj = regex.match(line)
p match_obj.to_a

--output:--
["8"]

You certainly don't have to use regex's to convert a string to a float
(or an int). Look at String#to_f and Kernel.Float.

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