Bool.Parse. In C# we can convert a string to a bool. This is done with bool.Parse or bool.TryParse—or by using a custom method with relaxed parsing rules.

Custom method. In the custom method, the strings TRUE and T should both evaluate to a true value. Further logic can be added—any truth value can be parsed.

Example. Consider the bool.Parse and bool.TryParse methods built into .NET. These are the easiest to use in programs—you don't need to add custom code.

using System;

string value = "true";
bool b = bool.Parse(value);
Console.WriteLine(b); // [1]

value = "False";
b = bool.Parse(value);
Console.WriteLine(b); // [2]

value = "Perls";
if (bool.TryParse(value, out b))
{
    Console.WriteLine("Not reached");
}
True
False

BoolParser. This method parses a string to see if it matches an equivalent of yes. It tests for strings that should evaluate to true, and if none matches, it considers the default false.

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine(BoolParser.GetValue("true"));  // True
        Console.WriteLine(BoolParser.GetValue("okay"));  // False
        Console.WriteLine(BoolParser.GetValue("T"));     // True
        Console.WriteLine(BoolParser.GetValue("False")); // False
        Console.WriteLine(BoolParser.GetValue("No"));    // False
        Console.WriteLine(BoolParser.GetValue("maybe")); // False
        Console.WriteLine(BoolParser.GetValue("YES"));   // True
        Console.WriteLine(BoolParser.GetValue("TRUE ")); // True
        Console.WriteLine(BoolParser.GetValue("f"));     // False
        Console.WriteLine(BoolParser.GetValue("1"));     // True
        Console.WriteLine(BoolParser.GetValue("0"));     // False

        Console.WriteLine(BoolParser.GetValue(bool.TrueString));  // True
        Console.WriteLine(BoolParser.GetValue(bool.FalseString)); // False
    }
}

/// <summary>
/// Parse strings into true or false bools using relaxed parsing rules
/// </summary>
public static class BoolParser
{
    /// <summary>
    /// Get the boolean value for this string
    /// </summary>
    public static bool GetValue(string value)
    {
        return IsTrue(value);
    }

    /// <summary>
    /// Determine whether the string is not True
    /// </summary>
    public static bool IsFalse(string value)
    {
        return !IsTrue(value);
    }

    /// <summary>
    /// Determine whether the string is equal to True
    /// </summary>
    public static bool IsTrue(string value)
    {
        try
        {
            // 1
            // Avoid exceptions
            if (value == null)
            {
                return false;
            }

            // 2
            // Remove whitespace from string
            value = value.Trim();

            // 3
            // Lowercase the string
            value = value.ToLower();

            // 4
            // Check for word true
            if (value == "true")
            {
                return true;
            }

            // 5
            // Check for letter true
            if (value == "t")
            {
                return true;
            }

            // 6
            // Check for one
            if (value == "1")
            {
                return true;
            }

            // 7
            // Check for word yes
            if (value == "yes")
            {
                return true;
            }

            // 8
            // Check for letter yes
            if (value == "y")
            {
                return true;
            }

            // 9
            // It is false
            return false;
        }
        catch
        {
            return false;
        }
    }
}
True
False
True
False
False
False
True
True
False
True
False
True
False
String input: true
Bool result:  True

String input: false
Bool result:  False

String input: t
Bool result:  True

String input: f
Bool result:  False

String input: yes
Bool result:  True

String input: no
Bool result:  False

String input: 1
Bool result:  True

String input: 0
Bool result:  False

String input: Is invalid
Bool result:  False

Note, usage. I needed this code when developing a configuration utility. I felt it would cause less worry for the users if the program was more accepting of slightly wrong values.

Summary. We looked at the bool.Parse and bool.TryParse methods. We saw an easy way to implement bool parsing with many input variants. Finally we implemented a custom parser.