Complex Boolean Logic

Part of the Logic & Flow section of Coddy's C# journey — lesson 9 of 66.

Boolean logic can become complex when combining multiple conditions. Understanding operator precedence and using parentheses helps write clear, correct expressions.

The order of precedence for boolean operators in C# is:

NOT (!)
AND (&&)
OR (||)

Here's an example of a complex boolean expression:

bool isValid = age >= 18 && (score > 70 || hasPriorExperience) && !isBlacklisted;

Use De Morgan's Laws to simplify complex negations:

// Instead of:
if (!(age >= 18 && score > 70))
{
    // This is equivalent to:
    if (age < 18 || score <= 70)
    {
        Console.WriteLine("Not eligible");
    }
}

Short-circuit evaluation: With && and ||, C# evaluates only what's necessary:

// If user is null, C# won't evaluate the second condition
if (user != null && user.IsActive)
{
    Console.WriteLine("Active user");
}

Use explicit parentheses for clarity, even when not strictly required:

bool result = (isWeekend || isHoliday) && (hour > 10 && hour < 20);

Challenge

Medium

Create a method called determineAccess that determines if a user has access to a system based on these rules:

Takes five parameters:
- isAdmin (bool): Whether the user is an administrator
- isLoggedIn (bool): Whether the user is currently logged in
- timeOfDay (int): The current hour (0-23)
- isMaintenanceMode (bool): Whether the system is in maintenance mode
- hasEmergencyAccess (bool): Whether the user has emergency access
Returns true when ANY of these conditions are true:
- The user is an admin AND is logged in
- The time is between business hours (9-17 inclusive) AND the user is logged in AND the system is NOT in maintenance mode
- The user has emergency access

Cheat sheet

Boolean operator precedence in C# (highest to lowest):

NOT (!)
AND (&&)
OR (||)

Complex boolean expressions:

bool isValid = age >= 18 && (score > 70 || hasPriorExperience) && !isBlacklisted;

De Morgan's Laws for simplifying negations:

// Instead of:
if (!(age >= 18 && score > 70))
{
    // This is equivalent to:
    if (age < 18 || score <= 70)
    {
        Console.WriteLine("Not eligible");
    }
}

Short-circuit evaluation prevents errors by evaluating only what's necessary:

// If user is null, C# won't evaluate the second condition
if (user != null && user.IsActive)
{
    Console.WriteLine("Active user");
}

Use explicit parentheses for clarity:

bool result = (isWeekend || isHoliday) && (hour > 10 && hour < 20);

Try it yourself

public class DetermineAccess
{
    // Implement the determineAccess method
    public static bool determineAccess(bool isAdmin, bool isLoggedIn, int timeOfDay, bool isMaintenanceMode, bool hasEmergencyAccess)
    {
        // Write your code here
        
    }
}