Regex.Match("User name (sales)", @"(([^)]*))").Groups[1].Value

(             # Escaped parenthesis, means "starts with a '(' character"
    (          # Parentheses in a regex mean "put (capture) the stuff
               #     in between into the Groups array"
       [^)]    # Any character that is not a ')' character
       *       # Zero or more occurrences of the aforementioned "non ')' char"
    )          # Close the capturing group
)             # "Ends with a ')' character"

string input = "User name (sales)";
string output = input.Split('(', ')')[1];

string s = "User name (sales)";
int start = s.IndexOf("(") + 1;
int end = s.IndexOf(")", start);
string result = s.Substring(start, end - start);

public string GetSubstringByString(string a, string b, string c)
    {
        return c.Substring((c.IndexOf(a) + a.Length), (c.IndexOf(b) - c.IndexOf(a) - a.Length));
    }

GetSubstringByString("(", ")", "User name (sales)")

sales

(([a-z]+?))

Regex regex = new Regex("\((?<TextInsideBrackets>\w+)\)");
        string incomingValue = "Username (sales)";
        string insideBrackets = null;
        Match match = regex.Match(incomingValue);
        if(match.Success)
        {
            insideBrackets = match.Groups["TextInsideBrackets"].Value;
        }

string input = "User name (sales)";

string output = input.Substring(input.IndexOf('(') + 1, input.IndexOf(')') - input.IndexOf('(') - 1);

using System;
using System.Text.RegularExpressions;

private IEnumerable<string> GetSubStrings(string input, string start, string end)
{
    Regex r = new Regex(Regex.Escape(start) +`"(.*?)"`  + Regex.Escape(end));
    MatchCollection matches = r.Matches(input);
    foreach (Match match in matches)
    yield return match.Groups[1].Value;
}

string test = "(test)";
string word = Regex.Match(test, @"((w+))").Groups[1].Value;
Console.WriteLine(word);

input.Remove(input.IndexOf(')')).Substring(input.IndexOf('(') + 1);

string input= "my name is (Jayne C)";
int start = input.IndexOf("(");
int stop = input.IndexOf(")");
string output = input.Substring(start+1, stop - start - 1);

string input = "my name is (Jayne C)";
string output  = input.Substring(input.IndexOf("(") +1, input.IndexOf(")")- input.IndexOf("(")- 1);

// Returns the text between 'start' and 'end'.
string ExtractBetween(string text, string start, string end)
{
  int iStart = text.IndexOf(start);
  iStart = (iStart == -1) ? 0 : iStart + start.Length;
  int iEnd = text.LastIndexOf(end);
  if(iEnd == -1)
  {
    iEnd = text.Length;
  }
  int len = iEnd - iStart;

  return text.Substring(iStart, len);
}

string result = ExtractBetween("User name (sales)", "(", ")");

string separator = "n";     //line terminator

 string output;
 string input= "HowAreYou?nLets go there!";

 output = input.Substring(0, input.IndexOf(separator));

public static string GetNestedString(this string str, char start, char end)
{
    int s = -1;
    int i = -1;
    while (++i < str.Length)
        if (str[i] == start)
        {
            s = i;
            break;
        }
    int e = -1;
    while(++i < str.Length)
        if (str[i] == end)
        {
            e = i;
            break;
        }
    if (e > s)
        return str.Substring(s + 1, e - s - 1);
    return null;
}

public static string GetNestedString(this string str, char start, char end)
{
    int s = -1;
    int i = -1;
    while (++i < str.Length)
        if (str[i] == start)
        {
            s = i;
            break;
        }
    int e = -1;
    int depth = 0;
    while (++i < str.Length)
        if (str[i] == end)
        {
            e = i;
            if (depth == 0)
                break;
            else
                --depth;
        }
        else if (str[i] == start)
            ++depth;
    if (e > s)
        return str.Substring(s + 1, e - s - 1);
    return null;
}

public String getSubstring(String startChar, String endChar, String initString)
{
    return initString.substring((initString.indexOf(startChar) + 1), (initString.indexOf(endChar)));
}

int start = input.IndexOf("(") + 1;
int end = input.IndexOf(")") - start;
output = input.Substring(start, end);