C# Remove special characters

Question

I want to remove all special characters from a string. Allowed characters are A-Z (uppercase or lowercase), numbers (0-9), underscore (_), white space ( ), pecentage(%) or the d

Answer 1

StringBuilder sb = new StringBuilder();
foreach (char c in input)
{
    if (char.IsLetterOrDigit(c) || "_ %.".Contains(c.ToString()))
        sb.Append(c);
}
return sb.ToString();