Tools: 16. C# (Switch Statement)

0. The Real Goal of This Lesson ## 1. Why Do We Need switch? ## ❌ Using if / else ## When switch Is the Right Tool ## 2. The Basic Structure of switch ## Key Concept: What Is an Expression? ## 3. TODO App Example — Full Runnable Code ## 4. Why Is break Required? ## Try This ## The Rule ## 5. The Exact Meaning of default ## 6. Handling Case Sensitivity ## Cleaner Approach (Recommended) ## 7. Grade Conversion Exercise ## 8. When to Use switch vs if ## 9. The Sensory Model You Must Develop ## One-Line Summary This is not about learning syntax. The real goal is to understand one idea physically: “How to split execution flow into multiple exact branches based on a single value.” If this is not clear: Everything turns into memorized structure instead of intentional logic. Let’s start with a problem. Logically, there is nothing wrong here. The structure says “conditional logic.” But the intent is actually “exact value matching.” One single value Must be matched against multiple exact possibilities. This is not range logic. This is exact matching logic. That is what switch models. Any code that evaluates to a value. Here, choice is the expression. It is evaluated once. Its result is compared against each case label. Run this directly in Rider. Notice the structure: Evaluate once → Match exactly → Execute → Exit By default, switch behaves like this: Once a matching case is found, execution continues downward unless explicitly stopped. That means without break, execution “falls through” to the next case. Remove break from one case: You will see additional cases executing. This is how switch works. Each case must end with: Otherwise, control continues to the next case. break exits the switch block. return exits the entire method. These are not interchangeable concepts. Execute this block if none of the cases match. It is equivalent to else in an if/else structure. It guarantees that unmatched input is handled. Without default, unmatched input is silently ignored. That is rarely desirable. Multiple case labels can share one block. If either value matches, execute the same logic. You only need one case. This reduces duplication. Important observation: When using return, break is unnecessary. return terminates the entire method immediately. Control does not return to the switch. Use the tool that matches the logical structure of the problem. Not the tool you feel more comfortable with. A structure for routing execution based on one evaluated value. A structure for evaluating logical conditions. They are not interchangeable. They represent different mental models. A switch statement evaluates one expression and dispatches execution to exactly matching branches with explicit control over termination. Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse CODE_BLOCK: if (choice == "A") { Console.WriteLine("Add"); } else if (choice == "S") { Console.WriteLine("Subtract"); } else if (choice == "M") { Console.WriteLine("Multiply"); } else { Console.WriteLine("Invalid choice"); } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: if (choice == "A") { Console.WriteLine("Add"); } else if (choice == "S") { Console.WriteLine("Subtract"); } else if (choice == "M") { Console.WriteLine("Multiply"); } else { Console.WriteLine("Invalid choice"); } CODE_BLOCK: if (choice == "A") { Console.WriteLine("Add"); } else if (choice == "S") { Console.WriteLine("Subtract"); } else if (choice == "M") { Console.WriteLine("Multiply"); } else { Console.WriteLine("Invalid choice"); } CODE_BLOCK: switch (expression) { case value1: // code break; case value2: // code break; default: // fallback break; } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: switch (expression) { case value1: // code break; case value2: // code break; default: // fallback break; } CODE_BLOCK: switch (expression) { case value1: // code break; case value2: // code break; default: // fallback break; } CODE_BLOCK: switch (choice) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: switch (choice) CODE_BLOCK: switch (choice) CODE_BLOCK: using System; class Program { static void Main() { Console.WriteLine("Choose option: A, S, M"); string choice = Console.ReadLine(); switch (choice) { case "A": Console.WriteLine("Addition selected"); break; case "S": Console.WriteLine("Subtraction selected"); break; case "M": Console.WriteLine("Multiplication selected"); break; default: Console.WriteLine("Invalid choice"); break; } Console.ReadKey(); } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: using System; class Program { static void Main() { Console.WriteLine("Choose option: A, S, M"); string choice = Console.ReadLine(); switch (choice) { case "A": Console.WriteLine("Addition selected"); break; case "S": Console.WriteLine("Subtraction selected"); break; case "M": Console.WriteLine("Multiplication selected"); break; default: Console.WriteLine("Invalid choice"); break; } Console.ReadKey(); } } CODE_BLOCK: using System; class Program { static void Main() { Console.WriteLine("Choose option: A, S, M"); string choice = Console.ReadLine(); switch (choice) { case "A": Console.WriteLine("Addition selected"); break; case "S": Console.WriteLine("Subtraction selected"); break; case "M": Console.WriteLine("Multiplication selected"); break; default: Console.WriteLine("Invalid choice"); break; } Console.ReadKey(); } } CODE_BLOCK: case "A": Console.WriteLine("Addition selected"); Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: case "A": Console.WriteLine("Addition selected"); CODE_BLOCK: case "A": Console.WriteLine("Addition selected"); CODE_BLOCK: case "A": case "a": Console.WriteLine("Addition selected"); break; Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: case "A": case "a": Console.WriteLine("Addition selected"); break; CODE_BLOCK: case "A": case "a": Console.WriteLine("Addition selected"); break; CODE_BLOCK: switch (choice.ToUpper()) Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: switch (choice.ToUpper()) CODE_BLOCK: switch (choice.ToUpper()) CODE_BLOCK: using System; class Program { static void Main() { Console.WriteLine("Enter score (0-10):"); int points = int.Parse(Console.ReadLine()); string grade = ConvertPointsToGrade(points); Console.WriteLine($"Grade: {grade}"); Console.ReadKey(); } static string ConvertPointsToGrade(int points) { switch (points) { case 9: case 10: return "A"; case 7: case 8: return "B"; case 5: case 6: return "C"; case 3: case 4: return "D"; case 0: case 1: case 2: return "F"; default: return "!"; } } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: using System; class Program { static void Main() { Console.WriteLine("Enter score (0-10):"); int points = int.Parse(Console.ReadLine()); string grade = ConvertPointsToGrade(points); Console.WriteLine($"Grade: {grade}"); Console.ReadKey(); } static string ConvertPointsToGrade(int points) { switch (points) { case 9: case 10: return "A"; case 7: case 8: return "B"; case 5: case 6: return "C"; case 3: case 4: return "D"; case 0: case 1: case 2: return "F"; default: return "!"; } } } CODE_BLOCK: using System; class Program { static void Main() { Console.WriteLine("Enter score (0-10):"); int points = int.Parse(Console.ReadLine()); string grade = ConvertPointsToGrade(points); Console.WriteLine($"Grade: {grade}"); Console.ReadKey(); } static string ConvertPointsToGrade(int points) { switch (points) { case 9: case 10: return "A"; case 7: case 8: return "B"; case 5: case 6: return "C"; case 3: case 4: return "D"; case 0: case 1: case 2: return "F"; default: return "!"; } } } - switch becomes just another keyword - break feels arbitrary - Control flow design remains shallow - The same variable is compared repeatedly - The pattern must be mentally reconstructed by the reader - The intent is not immediately visible - Is choice equal to "A"? - Is it equal to "S"? - Is it equal to "M"? - Or none of them? - A method call - A calculation - "a" becomes "A" - "A" remains "A"