given a string enclosed in round bracckets code example

Example 1: c# regex to find number between parenthesis

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

Example 2: c# get string in parentheses

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