In this lesson, we'll continue building our hotel cost application from our previous lesson. We'll explore two new C# operators along the way: || and !

Currently, our two else if statements result in the same response to the user:

using System;

class HotelCost
{
  static void Main()
  {
    Console.WriteLine("In what season are you booking a stay?");
    string season = Console.ReadLine();

    Console.WriteLine("On the weekend or a weeknight?");
    string dayOfWeek = Console.ReadLine();

    bool summer = season == "summer";
    bool weekend = dayOfWeek == "weekend";

    if (summer && weekend)
    {
      Console.WriteLine("Your stay is probably going to be pretty expensive. It's both peak travel season AND the weekend.");
    }
    else if (summer)
    {
      Console.WriteLine("Your stay might be more expensive than normal!");
    }
    else if (weekend)
    {
      Console.WriteLine("Your stay might be more expensive than normal!");
    }
    else
    {
      Console.WriteLine("Your stay might be expensive, but it could be worse!");
    }
  }
}

Maintaining DRY Branching with ||

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We can DRY up our code by using the || operator. || means or. Check it out:

using System;

class HotelCost
{
  static void Main()
  {
    Console.WriteLine("In what season are you booking a stay?");
    string season = Console.ReadLine();

    Console.WriteLine("On the weekend or a weeknight?");
    string dayOfWeek = Console.ReadLine();

    bool summer = season == "summer";
    bool weekend = dayOfWeek == "weekend";

    if (summer && weekend)
    {
      Console.WriteLine("Your stay is probably going to be pretty expensive. It's both peak travel season AND the weekend.");
    }
    else if (summer || weekend)
    {
      Console.WriteLine("Your stay might be more expensive than normal!");
    }
    else
    {
      Console.WriteLine("Your stay might be expensive, but it could be worse!");
    }
  }
}

Both || and && evaluate two separate booleans. While && only evaluates to true if both booleans are true, || will evaluate to true if either boolean is true. For || to evaluate to false, both booleans must be false.

• In the code above, the first conditional still uses the && operator. If both summer and weekend are true, the program prints "Your stay is probably going to be pretty expensive. It's both peak travel season AND the weekend."

• Otherwise, the program moves to the next conditional. This conditional now states else if ( summer || weekend ). If either weekend or summer are true, this conditional will print "Your stay might be more expensive than normal!".

• If neither conditional is true, we can assume both are false. The program moves to the else statement, printing "Your stay might be expensive, but it could be worse!".

The ! Operator

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Finally, there is the bang operator !. This operator means "not". We can prepend this to any boolean and it will reverse the value of that boolean. For example:

using System;

class HotelCost
{
  static void Main()
  {
    Console.WriteLine("In what season are you booking a stay?");
    string season = Console.ReadLine();

    Console.WriteLine("On the weekend or a weeknight?");
    string dayOfWeek = Console.ReadLine();

    bool summer = season == "summer";
    bool weekend = dayOfWeek == "weekend";

    if (summer && weekend)
    {
      Console.WriteLine("Your stay is probably going to be pretty expensive. It's both peak travel season AND the weekend.");
    }
    else if (!(summer || weekend))
    {
      Console.WriteLine("Your stay will likely be the cheapest possible!");
    }
    else
    {
      Console.WriteLine("Your stay might be more expensive than normal!");
    }
  }
}

By adding the bang operator like this (!(summer || weekend)), we're looking for the opposite of (summer || weekend). In other words, neither boolean can be true for this condition to be met. Here, the else statement would run if one or the other is true, but not both.