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How to validate Regex

Im having a hard time with grouping parts of a Regex. I want to validate a few things in a string that follows this format: I-XXXXXX.XX.XX.XX
Validate that the first set of 6 X's (I-xxxxxx.XX.XX.XX) does not contain characters and its length is no more than 6.
Validate that the third set of X's (I-XXXXXX.XX.xx.XX) does not contain characters and is only 1 or 2.
Now, I have already validation on the last set of XX's to make sure the numbers are 1-8 using
string pattern1 = #"^.+\.(0?[1-8])$";
Match match = Regex.Match(TxtWBS.Text, pattern1);
if (match.Success)
;
else
{ errMessage += "WBS invalid"; errMessage +=
Environment.NewLine; }
I just cant figure out how to target specific parts of the string. Any help would be greatly appreciated and thank you in advance!

You're having some trouble adding new validation to this string because it's very generic. Let's take a look at what you're doing:
^.+\.(0?[1-8])$
This finds the following:
^ the start of the string
.+ everything it can, other than a newline, basically jumping the engine's cursor to the end of your line
\. the last period in the string, because of the greedy quantifier in the .+ that comes before it
0? a zero, if it can
[1-8] a number between 1 and 8
()$ stores the two previous things in a group, and if the end of the string doesn't come after this, it may even backtrace and try the same thing from the second to last period instead, which we know isn't a great strategy.
This ends up matching a lot of weird stuff, like for example the string The number 0.1
Let's try patterning something more specific, if we can:
^I-(\d{6})\.(\d{2})\.(\d{1,2})\.([1-8]{2})$
This will match:
^I- an I and a hyphen at the start of the string
(\d{6}) six digits, which it stores in a capture group
\. a period. By now, if there was any other number of digits than six, the match fails instead of trying to backtrace all over the place.
(\d{2})\. Same thing, but two digits instead of six.
(\d{1,2})\. Same thing, the comma here meaning it can match between one and two digits.
([1-8]{2}) Two digits that are each between 1 and 8.
$ The end of the string.
I hope I understood what exactly you're trying to match here. Let me know if this isn't what you had in mind.

This regex:
^.-[0-9]{6}(\.[1-8]{1,2}){3}$
will validate the following:
The first character can be any character, but is of length 1
It is followed by a dash
The dash is followed by exactly 6 numbers 0 - 9. (If this could be less than 6 characters - for example, between 3 and 6 characters - just replace {6} with {3,6}).
This is followed by 3 groups of characters. Each of this groups are proceeded by a period, are of length 1 or 2, and can be any number 1 - 8.
An example of a valid string is:
I-587954.12.34.56
This is also valid:
I-587954.1.3.5
But this isn't:
I-587954.12.80.356
because the second-to-last group contains a 0, and because the last group is of length 3.
Pleas let me know if I have misunderstood any of the rules.

^I-([0-9]{1,6})\.(.{1,2})\.(0[1-2])\.(.{1,2})$
groups delimited by . (\.) :
([0-9]{1,6}) - 1-6 digits
(.{1,2}) - 1-2 any single character
(0[1-2]) - 01 or 02
(.{1,2}) - 1-2 any single character
you can write and easy test regex on your input data, just google "regex online"

Converting a String of input into Inches

What I would like to do is to take input string, in architectural format and convert it to a double in inches.
For example:
Input: (String) Output: (Double)
1'-2" 14
1'-2 1/2" 14.5
1'2 3/16" 14.1875
1' 12
12 12
12" 12
1'0.5 12.5
1'0.5" 12.5
1'-0.5 12.5
1'-0.5" 12.5
I know I would need to iterate through every character in the string and test a bunch of cases but I did not know if there was some built in function within c# or within some other resource that could do this for me and not make me re-invent the wheel.

Regex for the win!
Okay, if you're new to Regex, it's basically a way of parsing strings. So, realistically, what does your input consist of?
At a high level, you've got one of these three possibilities:
Composite: Number, followed by ', followed by either a - or space,
followed by a number, and optionally ending with a "
Feet Only: Number, followed by a '
Inches Only: Number, optionally followed by a "
And those 'Number's?
Possibilities:
1+ digits (aka, "23")
1+ digits, a '.', and 1+ digits (aka, "32.43")
1+ digits, a space, 1+ digits, a slash, and 1+ digits (aka, "32
13/16")
1+ digits, a slash, and 1+ digits (aka, "13/16")
Okay, so first up, we need a regex for one of your "numbers":
\d+|\d+.\d+|\d+ \d+\/\d+|\d+\/\d+
(Looks complicated, but see these two pages for reference: http://www.rexegg.com/regex-quickstart.html and https://regex101.com/)
Now, just so our regex'es don't get too complicated, you could do something like this:
string regexSnippetForNumber = #"\d+|\d+.\d+|\d+ \d+\/\d+|\d+\/\d+";
string regexForComposite =
"^(" + regexSnippetForNumber + ")'[ -]" +
"(" + regexSnippetForNumber + ")\"?$"
... and then, if the input matches regexForComposite, you use the two capturing groups to get the two numbers. (Which you'd have to parse to get the numerical value.)
Hopefully that makes sense and can get you close enough to the finish line. If you've never used Regexes before, I highly suggest you read up on them. They're incredibly handy when you need to do string parsing that can otherwise be really annoying (like this exact problem!)

Regular expression in C# for Number with Decimal Point & Commas

I need to enter amount in a textbox which allows numbers with decimal point and commas.
What is the regular expression for this?
I used the below
txtInitialAmountGuarDetails.ValidationSettings.RegularExpression.ValidationExpression
= #"^[-+]?\d*[0-9](|.\d*[0-9])(|,\d*[0-9])?$";
But it not working for large numbers like 300,000,000,000,000.

Build it up piecemeal. Given a US locale, a number with these rules has in order:
The string beginning: ^
An optional sign: [+-]?
Up to 3 digits: \d{1,3}
A comma followed by 3 digits, repeated any number of times: (?:,\d{3})*
An optional decimal point and decimal part: (?:[.]\d+)?
The string end: $
Do you have restrictions on the number of digits after the decimal point? Then change the last plus sign to {2} for 2 digits.
So, the regex is:
#"^[+-]?\d{1,3}(?:,\d{3})*(?:[.]\d+)?$"
Or, if you want to explain your work, use the x option and:
#"(?x) # Extended format.
^[+-]? # Optional sign.
\d{1,3} # Initial 1-3 digits.
(?:,\d{3})* # Any number of commas followed by 3 digits.
(?:[.]\d+)?$" # An optional decimal point followed by any number of digits.
But does C# have a locale-dependent validator already?

I have not run it, but you can try it out.
var regexp =/^\s*?([\d\,]+(\.\d{1,2})?|\.\d{1,2})\s*$/;

This works: \d{1,3}(,\d{3})*\.{0,1}(\d{3},)*\d{0,3}
As for the after the comma issue, any choice should be fine. If you go with commas, my regex works. If you do 5 digits then a space just replace the end with (\d{5}\s{1})*\d{0,5}. And ofcourse if you just dont use any deliminator after the decimal you just put \d*

You can try this regex too:
^([+-]?\d{1,3}(?:,\d{1,3})*(?:\.\d+)*)$
Keep in mind . has a specific meaning in regex engine so it is necessary to escape it.
I would also suggest you to not use regex for this task instead look at masked textbox.

try this one:
^([0-9]{3}[,.]|)+[0-9]{0,3}$
let me know if it needs any enhancements...

Regular Expression for float and percentage

I need regex patterns for floating point numbers with optional % sign at the end like
12.32
12.32%
0.32
.32
.32%
arbitrary length of numbers on left and right of floating point numbers. I need this to validate input in asp.net mvc app
UPDATE:
forgot following combinations
12%
35
45%

This regex should do it for you...
\d*\.\d+%?
Which means... zero or more digits (\d*) followed by a period (escaped \.) followed by one or more digits (\d+) followed by an optional % (%?)
Update: match whole numbers
\d*\.?\d+%?

\d*\.\d{1,}%?
This matches all your cases.
ADD:
I answered the question in the comment about the {1,}: since I wasn't sure if single digit after the decimal point would be a valid input for you (all your examples have at least 2 digits after the point) I didn't use the plus-notation but rather indicated the number of digits explicitly. Here the first number indicates the minimal and the second number (omitted here) the maximal number of the digits after the point. If you want that all your input values have at least 2 digits after the point, use {2,} instead of {1,}.

need a regex for a positive max 2 digits after . floating number

Hi
I need a C# regex for a positive floatin no with maximum 2 digits for decimals. Also the regex should check for letters and alphanumerical chars (not allow them) and not allow also the input value to be empty (0 characters).
Thanks

^[+]?[0-9]+([.][0-9]{1,2})?$
This will force it to have either a + or nothing at the start, followed by at least 1 number, then optional (decimal followed by 1 or 2 numbers)
For others, yes, I know of \d, :digit:, using \., etc. I just prefer using [0-9] and [.], it makes them stand out easier for me.