C# Boolean Logic and Conditions

Until now, every statement ran in order. Useful programs must sometimes choose: accept or reject an input, apply one shipping rate, show a warning, or stop. The rule behind that choice becomes a Boolean expression—an expression whose only possible results are true and false.

Comparison operators create Boolean results. == asks whether values are equal, != asks whether they differ, and <, <=, >, and >= compare ordered values. A single = assigns; a double == compares. Reading the expression as a question helps: is orderTotal greater than or equal to 100?

int availableSeats = 4;
int requestedSeats = 3;

bool enoughSeats = requestedSeats <= availableSeats;
Console.WriteLine(enoughSeats);

True

The && operator means both sides must be true. The || operator means at least one side must be true. The ! operator reverses a Boolean. Prefer combining named facts when a rule would otherwise become a dense line of punctuation.

C# short-circuits && and || from left to right. If the left side of && is false, the whole expression is already false, so the right side does not run. That behavior lets a program check text.Length only after confirming text is not null, and it can avoid unnecessary work.

int age = 21;
bool hasTicket = true;
bool isBanned = false;

bool canEnter = age >= 18 && hasTicket && !isBanned;
Console.WriteLine(canEnter);

True

In an if/else-if/else chain, C# tests from the top and runs the first matching block. Later branches are skipped even if their conditions would also be true. Order specific or higher-priority rules before broad rules.

A grade of 95 is also at least 80. Testing >= 80 first would label it B and never reach >= 90. This is not a compiler error; it is a logic error, which means the program runs but applies the wrong rule.

using System;

class Program
{
  static void Main()
  {
      int score = 86;

      if (score >= 90)
          Console.WriteLine("A");
      else if (score >= 80)
          Console.WriteLine("B");
      else if (score >= 70)
          Console.WriteLine("C");
      else
          Console.WriteLine("Needs review");
  }
}

B

switch is useful when one value is compared with a set of discrete cases, such as a menu command, status, or day category. It keeps the subject visible and makes the fallback explicit with default. if is usually clearer for ranges, unrelated conditions, or rules that combine several variables.

Every case in a traditional switch must end its path, commonly with break or return. Modern switch expressions can return a value more compactly, but the statement form below makes execution flow visible and works in the course compiler.

using System;

class Program
{
  static void Main()
  {
      string command = "save";

      switch (command)
      {
          case "open":
              Console.WriteLine("Opening file");
              break;
          case "save":
              Console.WriteLine("Saving file");
              break;
          case "quit":
              Console.WriteLine("Closing program");
              break;
          default:
              Console.WriteLine("Unknown command");
              break;
      }
  }
}

Saving file