How many ways to represent True and False

[This was originally posted at http://timstall.dotnetdevelopersjournal.com/how_many_ways_to_represent_true_and_false.htm]

I was recently serializing data from both the database and user input, and it made me reflect on how many ways you can represent a boolean value as a literal string. For an English-language app (no globalization), here are several ways to represent a boolean:

• TRUE / FALSE - converting from a literal string.
• T / F - users who only want to enter the first character.
• Yes / No - non-technical users who want "friendly" terms.
• Y / N - again, users who want to only enter the first character.
• 1/0 - A bit, such as how SQL Server stores booleans.

And of course, the first three options can be case insensitive and trimmed white space (i.e. "tRUe" becomes "TRUE").

I had talked about using Convert.ToString to convert different objects to string, so I'd initially look at it's related method: Convert.ToBoolean. But one quickly sees that that won't handle all the cases (and with good reason). The only literal string it takes from this group is "true"/"false". For example, it would handle converting the integer 1, but not the literal string "1". Having a single function that just converts these different inputs to a boolean is a nice convenience. Here's a sample:

public static bool ConvertToBoolean(string strVal)
{
  if (string.IsNullOrEmpty(strVal))
    return false;

  strVal = strVal.ToUpper().Trim();

  if (strVal == "TRUE" || strVal == "T" || strVal == "1" 
    || strVal == "YES" || strVal == "Y")
    return true;
  else if (strVal == "FALSE" || strVal == "F" || strVal == "0" 
    || strVal == "NO" || strVal == "N")
    return false;
  else
    throw new ArgumentException("Cannot convert '" 
    + strVal + "' to Boolean.");
}