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Regex to match 7 same digits in a number regardless of position

I want to match an 8 digit number. Currently, I have the following regex but It is failing in some cases.
(\d+)\1{6}
It matches only when a number is different at the end such as 44444445 or 54444444. However, I am looking to match cases where at least 7 digits are the same regardless of their position.
It is failing in cases like
44454444
44544444
44444544
What modification is needed here?

It's probably a bad idea to use this in a performance-sensitive location, but you can use a capture reference to achieve this.
The Regex you need is as follows:
(\d)(?:.*?\1){6}
Breaking it down:
(\d) Capture group of any single digit
.*? means match any character, zero or more times, lazily
\1 means match the first capture group
We enclose that in a non-capturing group {?:
And add a quantifier {6} to match six times

You can sort the digits before matching
string input = "44444445 54444444 44454444 44544444 44444544";
string[] numbers = input.Split(' ');
foreach (var number in numbers)
{
number = String.Concat(str.OrderBy(c => c));
if (Regex.IsMatch(number, #"(\d+)\1{6}"))
// do something
}
Still not a good idea to use regex for this though

The pattern that you tried (\d+)\1{6} matches 6 of the same digits in a row. If you want to stretch the match over multiple same digits, you have to match optional digits in between.
Note that in .NET \d matches more digits than 0-9 only.
If you want to match only digits 0-9 using C# without matching other characters in between the digits:
([0-9])(?:[0-9]*?\1){6}
The pattern matches:
([0-9]) Capture group 1
(?: Non capture group
[0-9]*?\1 Match optional digits 0-9 and a backreference to group 1
){6} Close non capture group and repeat 6 times
See a .NET Regex demo
If you want to match only 8 digits, you can use a positive lookahead (?= to assert 8 digits and word boundaries \b
\b(?=\d{8}\b)[0-9]*([0-9])(?:[0-9]*?\1){6}\d*\b
See another .NET Regex demo

Regex to find invalid characters in integer with whitespaces

I want to use regular expression (regex) to find invalid characters in a string. The string is a user input and when the regex finds invalid characters I want to give the user feedback which characters where invalid. Example warning message: "Only 0-9 and whitespace allowed. Found invalid characters: ab" when input was "- 10 a 0 b".
A valid string is:
integer
negative or positive
is allowed to have any amount of whitespace at any position.
So for example those VALID strings should NOT match the regex:
"-100"
"- 1 00"
" - 1 00"
"100"
" 1 0 0 "
"1 00"
While the regex should find matches in these INVALID strings:
"- 1 a 0 0 b" should match "a" and "b"
"- 1 a 0 0 -" should match "a" and "-"
I had a working regex for positive integers, until i found out that I forgot to include negative integers:
var regex = new Regex(#"[^0-9\s]")
var invalidCharacters = regex.Matches(text)
I have only very basic knowledge of regex. I tried out negating the regex to include negative integers, but it is not working:
new Regex(#"(?!-?[0-9\s])")
I hope someone can help me with this. If this can be solved easier by removing the whitespace requirement. Then please feel free to ignore the whitespace part.

I would approach this by thinking about the positive case first - which strings are valid? And then negate that with a negative lookaround.
I think this meets your requirements:
(?!\s*-?[\d\s]).
\s* will match any whitespace at the start
-? will optionally match a hyphen
[\d\s] will match numbers and whitespace
(?!expression) is a negative lookaround to negate the whole expression
The . at the end is a way to generate matches. The negative lookaround is just an assertion - it doesn't return any results.
It produces the desired results for the test cases in your question.

You may use
var invalidCharacters = Regex.Matches(text, #"[^0-9\s-]|(?<!^\s*)-");
See the regex demo (modified a bit as the demo is a test against a single multiline string.)
The regex matches:
[^0-9\s-] - a char other than an ASCII digit, any Unicode whitespace char or a - char
| - or
(?<!^\s*)- - a - char that is not preceded with the start of string any any 0+ whitespace chars.

Regular Expression: Section names with unknown length?

I have a text block that is formatted like this:
1.2.3.4.5 or 1.2222.3.4.5 or 1 or 1.2 etc
An unknow number of numbers and dots (sections of a legal document)
How can I capture the full section (1.2.3.4.5) into a group?
I use C# but any regex is fine, aI can translate it.

UPDATED
Use this Regex:
Regex.Matches(inputString, #"\d[\.\d]*(?<!\.)");
explain:
\d digits (0-9)
[.\d]* any character of: '.', digits (0-9)
(0 or more times, matching the most amount possible))
(?<! subexpression) Zero-width negative lookbehind assertion.

string s = "1.2.3.4.5 or 1.2222.3.4.5 or 1 or 1.2 or 2222.3333.111.5 etc";
var matches = Regex.Matches(s, #"\d+(\.\d+)*").Cast<Match>()
.Select(m => m.Value)
.ToArray();

well, if you know you can't go beyond 5, then you can do
#"1+((.2+)((.3+)((.4+)(.5+)?)?)?)?"
and you can expand on that pattern for every symbol, up to a finite number of symbols
the + means any number of occurrences of the symbol, but at least 1. IF 0 is valid, you can use * instead
put ?: after an opening parenthesies if you don't want the pattern to be captured
like example: (?:abc)
I ommitted them to make the regex more readable.
the ? after the parenthesies, means 1 or 0 of the preceding symbol.
Now if you don't know how far you string can go, for instance
"1.2.3.4......252525.262626.272727.......n.n.n" than my intuition tells me that you can't do that with regex.

How to make this regex allow spaces c#

I have a phone number field with the following regex:
[RegularExpression(#"^[0-9]{10,10}$")]
This checks input is exactly 10 numeric characters, how should I change this regex to allow spaces to make all the following examples validate
1234567890
12 34567890
123 456 7890
cheers!

This works:
^(?:\s*\d\s*){10,10}$
Explanation:
^ - start line
(?: - start noncapturing group
\s* - any spaces
\d - a digit
\s* - any spaces
) - end noncapturing group
{10,10} - repeat exactly 10 times
$ - end line
This way of constructing this regex is also fairly extensible in case you will have to ignore any other characters.

Use this:
^([\s]*\d){10}\s*$
I cheated :) I just modified this regex here:
Regular expression to count number of commas in a string
I tested. It works fine for me.

Use this simple regex
var matches = Regex.Matches(inputString, #"([\s\d]{10})");
EDIT
var matches = Regex.Matches(inputString, #"^((?:\s*\d){10})$");
explain:
^ the beginning of the string
(?: ){10} group, but do not capture (10 times):
\s* whitespace (0 or more times, matching the most amount possible)
\d digits (0-9)
$ before an optional \n, and the end of the string

Depending on your problem, you might consider using a Match Evaluator delegate, as described in http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.matchevaluator.aspx
That would make short work of the issue of counting digits and/or spaces

Something like this i think ^\d{2}\s?\d\s?\d{3}\s?\d{4}$
There are variants : 10 digits or 2 digits space 8 digits or 3 digits space 3 digits space 4 digits.
But if you want only this 3 variants use something like this
^(?:\d{10})|(?:\d{2}\s\d{8})|(?:\d{3}\s\d{3}\s\d{4})$

RegEx for limited decimal

New to regex syntax here. Trying to write a regex to provide some input validation.
What I need is a regex to match a whole number, or a decimal with exactly one digit past the decimal.
Good Match
1
12
100
1.1
100.1
1.0
No Match
1.22
1.
0
012
Here is what I came up with but it doesn't work:
Regex.IsMatch(paidHours, "\\d+[.]?[0-9]?")

You can try with:
Regex.IsMatch(paidHours, "^\\d+(\\.\\d)?$")

Regex.IsMatch(paidHours, #"^\d+(\.\d)?$")

Edited answer after OP question edit.
Regex.IsMatch(paidHours, #"^[1-9][0-9]*(\.[0-9])?$");
Explanation:
^ : Start of the String
[1-9] : A single number between 1 and 9
[0-9]* : Zero or more number(s) between 0 and 9
([0-9]? would match zero or one number and the String "100" would not match the regex)
( : Start of a group
\. : A point
[0-9] : A single number between 0 and 9
)? : End of the group. The group must be repeated zero or one time
$ : End of the String
Please note that \d is not exactly equivalent to [0-9]: \d matches any unicode digit. For instance, this character ௮ will be matched if you use \d but won't be if you use [0-9].

Try to specify beggining/end of the line:
#"^\d+[.]?[0-9]?$"
You regex won't work since ie 1.234 was a match wit 1.2, if you don't specify you want the string ends with the '$' sign.