C# Conditional Statements

Conditional statements are fundamental constructs in C# that allow developers to control the flow of execution based on certain conditions. They enable programs to make decisions, execute different code blocks, and handle various scenarios dynamically. Understanding and effectively using conditional statements is essential for building robust and flexible applications.

1. Overview of Conditional Statements

2. The `if` Statement

if (condition)
{
    // Code to execute if condition is true
}

using System;

class Program
{
    static void Main()
    {
        int number = 10;

        if (number > 5)
        {
            Console.WriteLine("Number is greater than 5.");
        }
    }
}

Output:
Number is greater than 5.

3. The `if-else` Statement

if (condition)
{
    // Code to execute if condition is true
}
else
{
    // Code to execute if condition is false
}

using System;

class Program
{
    static void Main()
    {
        int number = 3;

        if (number % 2 == 0)
        {
            Console.WriteLine("Number is even.");
        }
        else
        {
            Console.WriteLine("Number is odd.");
        }
    }
}

Output:
Number is odd.

4. The `if-else if-else` Ladder

if (condition1)
{
    // Code to execute if condition1 is true
}
else if (condition2)
{
    // Code to execute if condition2 is true
}
else
{
    // Code to execute if all above conditions are false
}

using System;

class Program
{
    static void Main()
    {
        int score = 85;

        if (score >= 90)
        {
            Console.WriteLine("Grade: A");
        }
        else if (score >= 80)
        {
            Console.WriteLine("Grade: B");
        }
        else if (score >= 70)
        {
            Console.WriteLine("Grade: C");
        }
        else
        {
            Console.WriteLine("Grade: F");
        }
    }
}

Output:
Grade: B

5. The `switch` Statement

switch (expression)
{
    case value1:
        // Code to execute if expression == value1
        break;
    case value2:
        // Code to execute if expression == value2
        break;
    default:
        // Code to execute if expression doesn't match any case
        break;
}

using System;

class Program
{
    static void Main()
    {
        char grade = 'B';

        switch (grade)
        {
            case 'A':
                Console.WriteLine("Excellent!");
                break;
            case 'B':
                Console.WriteLine("Well done!");
                break;
            case 'C':
                Console.WriteLine("Good.");
                break;
            case 'D':
                Console.WriteLine("You passed.");
                break;
            case 'F':
                Console.WriteLine("Better try again.");
                break;
            default:
                Console.WriteLine("Invalid grade.");
                break;
        }
    }
}

Output:
Well done!

6. The Ternary Operator

condition ? expression_if_true : expression_if_false;

using System;

class Program
{
    static void Main()
    {
        int age = 20;
        string category = age >= 18 ? "Adult" : "Minor";
        Console.WriteLine($"Category: {category}");
    }
}

Output:
Category: Adult

7. The Null-Coalescing Operator

expression ?? default_value;

using System;

class Program
{
    static void Main()
    {
        string input = null;
        string result = input ?? "Default Value";
        Console.WriteLine($"Result: {result}");
    }
}

Output:
Result: Default Value

8. Pattern Matching with `switch`

using System;

class Program
{
    static void Main()
    {
        object obj = "Hello, World!";

        switch (obj)
        {
            case int i:
                Console.WriteLine($"Integer: {i}");
                break;
            case string s:
                Console.WriteLine($"String: {s}");
                break;
            case null:
                Console.WriteLine("Null value.");
                break;
            default:
                Console.WriteLine("Unknown type.");
                break;
        }
    }
}

Output:
String: Hello, World!

9. Switch Expressions

var result = expression switch
{
    pattern1 => value1,
    pattern2 => value2,
    _ => default_value
};

using System;

class Program
{
    static void Main()
    {
        char grade = 'A';
        string message = grade switch
        {
            'A' => "Excellent!",
            'B' => "Well done!",
            'C' => "Good.",
            'D' => "You passed.",
            'F' => "Better try again.",
            _ => "Invalid grade."
        };
        Console.WriteLine(message);
    }
}

Output:
Excellent!

10. Expression-Bodied Conditional Statements

using System;

class Program
{
    static void Main()
    {
        int number = 7;
        Console.WriteLine(GetParity(number)); // Output: Odd
    }

    static string GetParity(int num) => num % 2 == 0 ? "Even" : "Odd";
}

Output:
Odd

11. Best Practices for Using Conditional Statements

12. Common Mistakes and How to Avoid Them

using System;

class Program
{
  static void Main()
  {
      int day = 2;
      switch (day)
      {
          case 1:
              Console.WriteLine("Monday");
          case 2:
              Console.WriteLine("Tuesday");
          default:
              Console.WriteLine("Another day");
      }
  }
}

Output:
Tuesday
Another day

string result = condition1 ? (condition2 ? "A" : "B") : "C";

switch (value)
{
  case 1:
      // Do something
      break;
  case 2:
      // Do something
      break;
  // Missing default case
}

13. Advanced Topics

using System;

class Program
{
  static void Main()
  {
      bool a = false;
      bool result = a && MethodThatReturnsTrue();
      Console.WriteLine($"Result: {result}"); // Output: Result: False
  }

  static bool MethodThatReturnsTrue()
  {
      Console.WriteLine("Method executed.");
      return true;
  }
}

Output:
Result: False

using System;

class Program
{
  static void Main()
  {
      int number = 1;
      switch (number)
      {
          case 1:
              Console.WriteLine("One");
              goto case 2;
          case 2:
              Console.WriteLine("Two");
              break;
      }
  }
}

Output:
One
Two

using System;

class Program
{
  static void Main()
  {
      int number = 15;

      switch (number)
      {
          case int n when (n % 2 == 0):
              Console.WriteLine("Even number.");
              break;
          case int n when (n % 2 != 0):
              Console.WriteLine("Odd number.");
              break;
          default:
              Console.WriteLine("Unknown number.");
              break;
      }
  }
}

Output:
Odd number.

14. Real-World Example: User Authentication

using System;

class Program
{
    static void Main()
    {
        string role = "Admin";

        if (role == "Admin")
        {
            Console.WriteLine("Access granted to all resources.");
        }
        else if (role == "User")
        {
            Console.WriteLine("Access granted to limited resources.");
        }
        else
        {
            Console.WriteLine("Access denied.");
        }

        // Using switch statement
        switch (role)
        {
            case "Admin":
                Console.WriteLine("Admin Dashboard");
                break;
            case "User":
                Console.WriteLine("User Dashboard");
                break;
            default:
                Console.WriteLine("Guest Dashboard");
                break;
        }

        // Using ternary operator
        string access = role == "Admin" ? "Full Access" : "Restricted Access";
        Console.WriteLine($"Access Level: {access}");
    }
}

Output:
Access granted to all resources.
Admin Dashboard
Access Level: Full Access

15. Summary

Key points