How can I filter out the characters from a user inputed string in C#?

Question

How can I filter out the specific characters from an inputted string?

Please see below for how I have tried.

using System;

namespace PlainTest
{
    class arrayTest
    {
        static void Main(string[] args)
        {
            bool doAlways = true;
            int i = 1;
            do
            {
                Console.WriteLine("Test Number : {0}", i++);
                Console.Write("Key in the string: ");
                char[] alpha = { 'a', 'b', 'c' };
                string text = Console.ReadLine();
                string filterAlphabet = text.Trim(alpha);
                Console.WriteLine("The input is : {0}", text);
                Console.WriteLine("After trimmed the alpha a,b,c : {0}", filterAlphabet);
            } while (doAlways == true);
        }
    }
}

But when I tried with the character to be trimmed in between the numbers, the filter didn't work. Please see below for outputs for different inputs.

Test Number : 1
Key in the string: 123abc
The input is : 123abc
After trimmed the alpha a,b,c : 123

Test Number : 2
Key in the string: abc123
The input is : abc123
After trimmed the alpha a,b,c : 123

**Test Number : 3
Key in the string: aa1bb2cc3
The input is : aa1bb2cc3
After trimmed the alpha a,b,c : 1bb2cc3**

Test Number : 4
Key in the string: aaabbbccc123
The input is : aaabbbccc123
After trimmed the alpha a,b,c : 123

Test Number : 5
Key in the string: a12bc
The input is : a12bc
After trimmed the alpha a,b,c : 12

Test Number : 6
Key in the string:

Did you read the [documentation](https://msdn.microsoft.com/en-us/library/d4tt83f9(v=vs.110).aspx) for `String.Trim`? *Removes all **leading and trailing** occurrences of a set of characters specified in an array from the current String object.* A cursory Google search would show this documentation and additional references regarding this problem. Please make more research effort before asking your next question. [How much research effort is expected of Stack Overflow users?](https://meta.stackoverflow.com/questions/261592/how-much-research-effort-is-expected-of-stack-overflow-users) — tnw, Jul 25 '17 at 15:12

score 2 · Answer 1 · answered Jul 25 '17 at 15:14

Instead of using trim, you can loop through the string to look for the characters you want to remove and replace them with an empty string:

var alpha = new string[] { "a", "b", "c" };
foreach (var c in alpha)
{
    text = text.Replace(c, string.Empty);
}

score 0 · Answer 2 · edited Jul 12 '21 at 02:12

0

Trim(char[]) only removes leading or trailing characters, in the same way that Trim() removes leading/trailing white space. As soon as Trim hits a character that is not in the array, it stops (working both from the front and from the back). To get rid of your desired characters from anywhere, you need to use either Replace or a regular expression.

edited Jul 12 '21 at 02:12

Peter Mortensen

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answered Jul 25 '17 at 15:15

Jonathan Willcock

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nobody · Answer 3 · 2017-07-25T15:26:12.610

0

You can use Regex.

Instead of

string filterAlphabet = text.Trim(alpha);

Use regex to replace a,b,c

string filterAlphabet = Regex.Replace(text,"[abc]",string.Empty);

edited Jul 25 '17 at 15:26

answered Jul 25 '17 at 15:17

nobody

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1

@DaveBecker You are correct.I've updated it. – nobody Jul 25 '17 at 15:26

How can I filter out the characters from a user inputed string in C#?

3 Answers3