Pattern matching in switch in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Pattern matching in switch

Input value

↓

Switch statement

↓

Check case patterns one by one

↓

Match found?

No→Default case or exit

Yes↓

Execute matched case block

↓

End switch

The switch statement takes an input and checks it against multiple patterns. When a pattern matches, it runs the corresponding code block and then exits.

Execution Sample

C Sharp (C#)

object obj = 42;
switch (obj)
{
    case int i:
        Console.WriteLine($"Integer: {i}");
        break;
    case string s:
        Console.WriteLine($"String: {s}");
        break;
    default:
        Console.WriteLine("Unknown type");
        break;
}

This code checks the type of obj and prints a message depending on whether it is an int, a string, or something else.

Execution Table

Step	Input Value	Pattern Checked	Match Result	Action Taken	Output
1	42 (int)	case int i	Match	Print Integer: 42	Integer: 42
2	42 (int)	case string s	Not checked (already matched)	No action
3	42 (int)	default	Not checked (already matched)	No action
4	End	Switch ends	Exit	Switch ends

💡 Pattern matched at step 1, switch exits after executing matched case.

Variable Tracker

Variable	Start	After Step 1	After Step 4
obj	42 (int)	42 (int)	42 (int)
i (int)	undefined	42	42
s (string)	undefined	undefined	undefined

Key Moments - 3 Insights

Why does the switch stop checking other cases after a match?

Once a pattern matches (see execution_table step 1), the switch executes that case and exits to avoid running multiple cases.

What happens if no pattern matches the input?

If no pattern matches, the default case runs (if present). In the example, default is not reached because int matches first.

How does pattern matching extract variables like 'i'?

When a pattern matches, the matched value is assigned to the variable (e.g., 'i' gets 42 at step 1), so you can use it inside the case block.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'i' after step 1?

A undefined

B 42

C null

D string value

💡 Hint

Check variable_tracker row for 'i' after step 1.

At which step does the switch stop checking further patterns?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

See execution_table where match is found and switch exits.

If obj was a string "hello", which pattern would match?

A default

B case int i

C case string s

D No match

💡 Hint

Look at the patterns and their types in the code sample.

Concept Snapshot

switch (value) {
  case Type varName: // matches type and assigns
    // code block
    break;
  default:
    // fallback code
    break;
}
Pattern matching checks each case pattern in order and runs the first matching block.

Full Transcript

Pattern matching in switch lets you check the type or shape of a value and run code based on that. The switch statement tests each pattern one by one. When a pattern matches, it assigns the matched value to a variable and runs the case block. Then it stops checking further cases. If no pattern matches, the default case runs if present. This helps write clear and concise code that reacts to different data types or conditions.