16. C# (Switch Statement)

0. The Real Goal of This Lesson

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:

• switch becomes just another keyword
• break feels arbitrary
• Control flow design remains shallow

Everything turns into memorized structure instead of intentional logic.

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1. Why Do We Need switch?

Let’s start with a problem.

❌ Using if / else

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");
}

Logically, there is nothing wrong here.

The program works.

But structurally:

• The same variable is compared repeatedly
• The pattern must be mentally reconstructed by the reader
• The intent is not immediately visible

The structure says “conditional logic.”

But the intent is actually “exact value matching.”

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When switch Is the Right Tool

switch is used when:

One single value
Must be matched against multiple exact possibilities.

For example:

• Is choice equal to "A"?
• Is it equal to "S"?
• Is it equal to "M"?
• Or none of them?

This is not range logic.

This is exact matching logic.

That is what switch models.

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2. The Basic Structure of switch

switch (expression)
{
    case value1:
        // code
        break;

    case value2:
        // code
        break;

    default:
        // fallback
        break;
}

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Key Concept: What Is an Expression?

An expression is:

Any code that evaluates to a value.

Examples:

• A variable
• A method call
• A calculation

For example:

switch (choice)

Here, choice is the expression.

It is evaluated once.

Its result is compared against each case label.

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3. TODO App Example — Full Runnable Code

Run this directly in Rider.

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();
    }
}

Notice the structure:

Evaluate once → Match exactly → Execute → Exit

That is the model.

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4. Why Is break Required?

This is critical.

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.

---

Try This

Remove break from one case:

case "A":
    Console.WriteLine("Addition selected");

Run the program.

You will see additional cases executing.

This is not a bug.

This is how switch works.

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The Rule

Each case must end with:

• break
• or return

Otherwise, control continues to the next case.

break exits the switch block.

return exits the entire method.

These are not interchangeable concepts.

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5. The Exact Meaning of default

default means:

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.

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6. Handling Case Sensitivity

This works:

case "A":
case "a":
    Console.WriteLine("Addition selected");
    break;

Multiple case labels can share one block.

This means:

If either value matches, execute the same logic.

---

Cleaner Approach (Recommended)

switch (choice.ToUpper())

Now:

• "a" becomes "A"
• "A" remains "A"

You only need one case.

This reduces duplication.

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7. Grade Conversion Exercise

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 "!";
        }
    }
}

Important observation:

When using return, break is unnecessary.

Because:

return terminates the entire method immediately.

Control does not return to the switch.

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8. When to Use switch vs if

Situation	Recommended
Single value exact match	switch
Range comparison (>, <, >=)	if
Complex logical expressions	if

Use the tool that matches the logical structure of the problem.

Not the tool you feel more comfortable with.

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9. The Sensory Model You Must Develop

switch is:

A structure for routing execution based on one evaluated value.

if is:

A structure for evaluating logical conditions.

They are not interchangeable.

They represent different mental models.

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One-Line Summary

A switch statement evaluates one expression
and dispatches execution to exactly matching branches
with explicit control over termination.