Removing all non letter characters from a string in C#

Question

I want to remove all non letter characters from a string. When I say all letters I mean anything that isn't in the alphabet, or an apostrophe. This is the code I have.

public static string RemoveBadChars(string word)
{
    char[] chars = new char[word.Length];
    for (int i = 0; i < word.Length; i++)
    {
        char c = word[i];

        if ((int)c >= 65 && (int)c <= 90)
        {
            chars[i] = c;
        }
        else if ((int)c >= 97 && (int)c <= 122)
        {
            chars[i] = c;
        }
        else if ((int)c == 44)
        {
            chars[i] = c;
        }
    }

    word = new string(chars);

    return word;
}

It's close, but doesn't quite work. The problem is this:

[in]: "(the"
[out]: " the"

It gives me a space there instead of the "(". I want to remove the character entirely.

Answer 1

The Char class has a method that could help out. Use Char.IsLetter() to detect valid letters (and an additional check for the apostrophe), then pass the result to the string constructor:

var input = "(the;':";

var result = new string(input.Where(c => Char.IsLetter(c) || c == '\'').ToArray());

Output:

the'

Answer 2

You should use Regular Expression (Regex) instead.

public static string RemoveBadChars(string word)
{
    Regex reg = new Regex("[^a-zA-Z']");
    return reg.Replace(word, string.Empty);
}

If you don't want to replace spaces:

Regex reg = new Regex("[^a-zA-Z' ]");

Answer 3

A regular expression would be better as this is pretty inefficient, but to answer your question, the problem with your code is that you should use a different variable other than i inside your for loop. So, something like this:

public static string RemoveBadChars(string word)
{
    char[] chars = new char[word.Length];
    int myindex=0;
    for (int i = 0; i < word.Length; i++)
    {
        char c = word[i];

        if ((int)c >= 65 && (int)c <= 90)
        {
            chars[myindex] = c;
            myindex++;
        }
        else if ((int)c >= 97 && (int)c <= 122)
        {
            chars[myindex] = c;
            myindex++;
        }
        else if ((int)c == 44)
        {
            chars[myindex] = c;
            myindex++;
        }
    }

    word = new string(chars);

    return word;
}