Regular expression to match number formats - ruby

Question

I'm trying to write a small program that asks a user to input a number and the program will determine if it's a valid number. The user can enter any kind of number (integer, float, scientific notation, etc.).
My question is what regular expression should be used to keep something like "7w" from being matched as a valid number? Also I would like the number 0 to exit the loop and end the program, but as it's written now 0 is matching valid like any other number. Any insight please?
x = 1
while x != 0
puts "Enter a string"
num = gets
if num.match(/\d+/)
puts "Valid"
else
puts "invalid"
end
if num == 0
puts "End of program"
x = num
end
end

Answer 1

You need to execute this script from the command line, not a text editor, as you will be prompt to enter a number.
This is the ultra compact version
def validate(n)
if (Float(n) != nil rescue return :invalid)
return :zero if n.to_f == 0
return :valid
end
end
print "Please enter a number: "
puts "#{num = gets.strip} is #{validate(num)}"
Output:
Please enter a number: 00
00 is zero
Here is a longer version that problably you can extend it to tweak it to your needs.
class String
def numeric?
Float(self) != nil rescue false
end
end
def validate(n)
if n.numeric?
return :zero if n.to_f == 0
return :valid
else
return :invalid
end
end
print "Please enter a number: "
puts "#{num = gets.strip} is #{validate(num)}"
And here is a test for all the possible cases
test_cases = [
"33", #int pos
"+33", #int pos
"-33", #int neg
"1.22", #float pos
"-1.22", #float neg
"10e5", #scientific notation
"X", #STRING not numeric
"", #empty string
"0", #zero
"+0", #zero
"-0", #zero
"0.00000", #zero
"+0.00000", #zero
"-0.00000", #zero
"-999999999999999999999995444444444444444444444444444444444444434567890.99", #big num
"-1.2.3", #version number
" 9 ", #trailing spaces
]
puts "\n** Test cases **"
test_cases.each do |n|
puts "#{n} is #{validate(n)}"
end
Which outputs:
Please enter a number: 12.34
12.34 is valid
** Test cases ** 33 is valid
+33 is valid
-33 is valid
1.22 is valid
-1.22 is valid
10e5 is valid
X is invalid
is invalid
0 is zero
+0 is zero
-0 is zero
0.00000 is zero
+0.00000 is zero
-0.00000 is zero
-999999999999999999999995444444444444444444444444444444444444434567890.99 is valid
-1.2.3 is invalid
9 is valid
Source for the idea of checking if its numeric:
How can I see if the string is numeric?
http://mentalized.net/journal/2011/04/14/ruby_how_to_check_if_a_string_is_numeric/

Answer 2

To start with, you are overcomplicating the loop, secondly, your regular expression needs to be a bit more explicit. Try something like this:
x = 1
while x != 0
puts "Enter a string"
num = gets.chomp
if num == "0"
puts "exiting with 0"
exit 0
elsif num.match(/^[0-9](\.[0-9])?$+/)
puts "Valid"
else
puts "invalid"
end
end
This expression will match any number that contains a digit or a decimal, and will fail to match anything containing letters. If the string entered is exactly 0, the script will exit with status 0.