CODEWITHSUNDEEP
c#string
DomMa
DomMa

Reputation: 151

How to count everything but letters at end of a string

I have a random string and need to know the number of non-letter / non-number characters at the end of it.

For example:

"Some text." should result in 1

"More text 123 !.?" should result in 4 (blanks included)

"Even more text 123" should result in 0

How can I do that?

Upvotes: 2

Views: 175

Answers (4)

Matthew Watson
Matthew Watson

Reputation: 109537

The problem with using Linq is that Enumerable.Reverse() makes a copy of the string as a char array and iterates backwards through it, which is not efficient. That might not matter at all to you, but a much more efficient approach is to just loop backwards over the string's characters like so:

string test = "the string to test !*&*& ";

int i;

for (i = test.Length - 1; i >= 0 && !char.IsLetterOrDigit(test[i]); --i)
    ;

int n = test.Length - i - 1; // n is the count of non-letter/non-digit chars

If you wanted it as a method to call:

public static int CountNonLetterDigitCharsAtEnd(string input)
{
    int i;

    for (i = input.Length - 1; i >= 0 && !char.IsLetterOrDigit(input[i]); --i)
        ;

    return input.Length - i - 1;
}

Upvotes: 1

codeteq
codeteq

Reputation: 1532

It's easy with LINQ:

using System.Linq;

This function also handles null strings and returns -1 for them.

    public static int CountNonLettersAtEnd(string input)
        => input?.Reverse().TakeWhile(c => !char.IsLetterOrDigit(c)).Count() ?? -1;

Upvotes: 0

Dmitrii Bychenko
Dmitrii Bychenko

Reputation: 186668

You can try Linq:

  string source = "More text 123 !.?";

  int result = source
    .Reverse()
    .TakeWhile(c => !char.IsLetterOrDigit(c))
    .Count();

Demo:

string[] tests = new string[] {
  "Some text.",
  "More text 123 !.?",
  "Even more text 123"
};

string demo = string.Join(Environment.NewLine, tests
  .Select(s => $"{s,-30} : {s.Reverse().TakeWhile(c => !char.IsLetterOrDigit(c)).Count()}"));

Console.Write(demo);

Outcome:

Some text.                     : 1
More text 123 !.?              : 4
Even more text 123             : 0

Upvotes: 6

Owen Pauling
Owen Pauling

Reputation: 11841

You could iterate backwards through the string and use Char.IsLetterOrDigit to determine if it's non-alphanumeric. When you find a letter or digit then stop and return the count.

Upvotes: 0

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