Converts a string to snake case.

Use Regex.Matches() with an appropriate regular expression to break the string into words.
Use string.Join() and string.ToLower() to convert the words to lowercase and combine them adding _ as a separator.


using System.Text.RegularExpressions;

public static partial class _30s 
  public static string ToSnakeCase(string str) 
    Regex pattern = new Regex(@"[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+");
    return string.Join("_", pattern.Matches(str)).ToLower();


_30s.ToSnakeCase("camelCase"); // "camel_case"
_30s.ToSnakeCase("some text"); // "some_text"
_30s.ToSnakeCase("some-mixed_string With spaces_underscores-and-hyphens"); // "some_mixed_string_with_spaces_underscores_and_hyphens"
_30s.ToSnakeCase("AllThe-small Things"); // "all_the_small_things"