create a regex that accepts only numbers but skips the first 10 characters unless they start with an x in csharp

To create a regex in C#, you can use the Regex class. Here's a regex pattern that matches only numbers with the exception of the first 10 characters, which will be skipped unless they start with an "x":

main.cs
string input = "xxxxxxxxxx123456";

if (Regex.IsMatch(input, @"^(x|.{0,10})\d+$"))
{
    Console.WriteLine("Valid input");
}
else
{
    Console.WriteLine("Invalid input");
}
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Explanation of the regex pattern:

• ^: Matches the start of the string
• (x|.{0,10}): Matches either an "x" or any character (represented by the dot), up to 10 times. This is enclosed in parentheses to allow the | (or) operator to work.
• \d+: Matches one or more digits
• $: Matches the end of the string

As a result, this pattern matches strings that start with an "x" followed by any number of digits, or strings that start with up to 10 characters followed by one or more digits. Any other characters in the input will result in an invalid match.