extract strings matching a regular expression vb.net

i have a text like following

1.
2.
3.
4. Test data 1
Please identify the ID number:
# 1016108
Please check if the number above matches the number below. The comparison result
should be "True or False". You should only compare the 7 digits:
a. #1016108
Please try to compare the results from Google OCR Engine and Microsoft OCR Engine.
And choose the one that suits for this task better.
Here is a third number # 123456, please DO NOT use this number for this task


i need to extract the numbers which are followed by # alone but not the third number as there is a text "third number" infront of it. also it is mentioned that i should not take this number for matching. so i need to extract first 2 numbers(only numbers) and match and say the result .

Code from Comment

Dim mc As MatchCollection
Dim i As Int32
mc = Regex.Matches(txt, "[#]([0-9]+)")
Dim results(mc.Count - 1) As String
For i = 0 To results.Length - 1
results(i) = mc(i).Value
Next
MessageBox.Show(results.ElementAt(0).ToString)


3 Answers
3

What you might do is match what you do not want and capture in a group what you do want using alternation. Your value will be in captured group 1.

bthird numbers*#s*d+b|#s*(d+)b

bthird numbers*#s*d+b|#s*(d+)b

Demo

Explanation

bthird numbers*#s*d+b

third number

b

#

s*

|

#s*(d+)b

#

d+

Or you might use a positive and a negative lookbehind to assert that what is on the left side is not third number:

(?<!bthird numbers*#s*)(?<=#s*)d+b

(?<!bthird numbers*#s*)(?<=#s*)d+b

Demo

Explanation

(?<!bthird numbers*#s*)

third number

b

#

s*

(?<=#s*)

#

d+b

Instead of matching third only, you might use S+ number instead of bthird number to match one or more times a non-whitespace character.

third

S+ number

bthird number

Dim mc As system.Text.RegularExpressions.MatchCollection


dim i as Int32
mc = system.Text.RegularExpressions.Regex.Matches(txt,"^#s?")

Dim results(mc.Count - 1) As String
For i = 0 To results.Length - 1
results(i) = mc(i).Value

Next
enter code here


Following your pattern and if I understand you correctly, you only want the numbers following # only if 'third number' is not written before the #

In that case this simple regex should do, check this out

Here is the regex for those who do not want to follow the link: #(.n| s.n)

This assumes that the # you want will have a new line at the end as seen from the example text you've posted.

This will also take care of the inconsistency where there can be a space after #

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