using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"1[5-9]\d{2,}|[2-9]\d{3,}|1\d{4,}";
string input = @"800
0800
1234
1511
1555
1789
2111
2345
3456
56756
123123
123123123
159999999999";
foreach (Match m in Regex.Matches(input, pattern))
{
Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
}
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx