Why pattern matching matters in C Sharp (C#) - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pattern matching with 'is' and 'switch'

What is the output of this C# code using pattern matching with is and switch?

C Sharp (C#)

object obj = 42;
string result = obj switch
{
    int i when i > 40 => "Greater than 40",
    int i => "Integer",
    string s => "String",
    _ => "Other"
};
Console.WriteLine(result);

A Other

B Integer

C String

D Greater than 40

💡 Hint

Look at the when condition in the switch expression.

The object obj is an integer 42, which matches the first pattern int i when i > 40. Since 42 > 40, it returns "Greater than 40".

🧠 Conceptual

intermediate

Why use pattern matching instead of if-else?

Which reason best explains why pattern matching is preferred over multiple if-else statements in C#?

A Pattern matching automatically fixes bugs in the code.

B Pattern matching runs faster than any <code>if-else</code> statement in all cases.

C Pattern matching allows clearer, more readable code by combining type checks and conditions in one expression.

D Pattern matching can only be used with strings, making it simpler.

💡 Hint

Think about code readability and combining checks.

Pattern matching combines type checks and conditions in a concise way, making code easier to read and maintain compared to many nested if-else statements.

🔧 Debug

advanced

Identify the error in pattern matching syntax

What error does this C# code produce?

C Sharp (C#)

object value = "hello";
switch (value)
{
    case string s && s.Length > 3:
        Console.WriteLine("Long string");
        break;
    default:
        Console.WriteLine("Other");
        break;
}

A SyntaxError: '&&' cannot be used in case patterns

B RuntimeException: NullReferenceException

C No error, prints 'Long string'

D CompileError: Missing colon after case

💡 Hint

Check the syntax for combining conditions in case patterns.

The code uses '&&' in a case pattern, which is invalid syntax in C#. The correct way is to use a when clause.

❓ Predict Output

advanced

Output of nested pattern matching with tuples

What is the output of this C# code using nested pattern matching with tuples?

C Sharp (C#)

var point = (X: 0, Y: 5);
string quadrant = point switch
{
    (0, 0) => "Origin",
    (0, var y) when y > 0 => "On positive Y axis",
    (var x, 0) when x > 0 => "On positive X axis",
    (var x, var y) when x > 0 && y > 0 => "Quadrant 1",
    _ => "Other"
};
Console.WriteLine(quadrant);

A On positive Y axis

B On positive X axis

C Quadrant 1

D Origin

💡 Hint

Look at the tuple values and the matching patterns carefully.

The tuple is (0, 5). It matches the pattern (0, var y) with y=5, and since 5 > 0, it returns "On positive Y axis".

🚀 Application

expert

Determine the number of matched cases in a pattern matching method

Given this method, how many times will the Console.WriteLine print "Matched" when called with the array new object[] { 5, "test", null, 10 }?

C Sharp (C#)

void CheckObjects(object[] items)
{
    foreach (var item in items)
    {
        if (item is int i && i > 5)
            Console.WriteLine("Matched");
    }
}

CheckObjects(new object[] { 5, "test", null, 10 });

A 2

B 1

C 3

D 0

💡 Hint

Count how many integers in the array are greater than 5.

Only the integer 10 is greater than 5, so "Matched" prints once.