Extract number at end of string in C#

Question

Probably over analysing this a little bit but how would stackoverflow suggest is the best way to return an integer that is contained at the end of a string.

Thus far

Answer 1

Without using RegEx that can be hard to understand, or Linq and array manipulation that can be slow, a simple loop in an extension method can be used.

It can be used for long or int or ulong or uint or other while adapting the + and - check.

It can be adapted to parse float and double or decimal too.

This method can also be written as a Parse to have exceptions.

Implementation

static public class StringHelper
{
  static public bool TryParseEndAsLong(this string str, out long result)
  {
    result = 0;
    if ( string.IsNullOrEmpty(str) )
      return false;
    int index = str.Length - 1;
    for ( ; index >= 0; index-- )
    {
      char c = str[index];
      bool stop = c == '+' || c == '-';
      if ( !stop && !char.IsDigit(c) )
      {
        index++;
        break;
      }
      if ( stop )
        break;
    }
    return index <= 0 ? long.TryParse(str, out result)
                      : long.TryParse(str.Substring(index), out result);
  }
} 

Test

test(null);
test("");
test("Test");
test("100");
test("-100");
test("100-200");
test("100 - 200");
test("Test 100");
test("Test100");
test("Test+100");
test("Test-100");
test("11111111111111111111");

Action test = str =>
{
  if ( str.TryParseEndAsLong(out var value) )
    Console.WriteLine($"\"{str}\" => {value}");
  else
    Console.WriteLine($"\"{str}\" has not a long at the end");
};

Output

"" has not a long at the end
"" has not a long at the end
"Test" has not a long at the end
"100" => 100
"-100" => -100
"100-200" => -200
"100 - 200" => 200
"Test 100" => 100
"Test100" => 100
"Test+100" => 100
"Test-100" => -100
"11111111111111111111" has not a long at the end