Pattern matching in switch in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to match the integer 5 in the switch expression.

C Sharp (C#)

int number = 5;
switch (number)
{
    case [1]:
        Console.WriteLine("Number is five");
        break;
    default:
        Console.WriteLine("Number is not five");
        break;
}

Drag options to blanks, or click blank then click option'

Aint

B"5"

Cnumber

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "5" instead of the integer 5.

Using the variable name instead of a constant value.

The case label must be the integer 5 to match the value of number.

2fill in blank

medium

Complete the code to use pattern matching to check if the object is a string.

C Sharp (C#)

object obj = "hello";
switch (obj)
{
    case [1] s:
        Console.WriteLine($"String with length {s.Length}");
        break;
    default:
        Console.WriteLine("Not a string");
        break;
}

Drag options to blanks, or click blank then click option'

Astring

Bint

Cbool

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong type like int or bool.

Forgetting to include the variable name after the type.

The pattern string s matches if obj is a string and assigns it to s.

3fill in blank

hard

Fix the error in the switch expression to correctly match a nullable int with value 10.

C Sharp (C#)

int? number = 10;
switch (number)
{
    case [1]:
        Console.WriteLine("Number is ten");
        break;
    default:
        Console.WriteLine("Number is not ten");
        break;
}

Drag options to blanks, or click blank then click option'

Aint n when n == 10

B10

Cint? n when n == 10

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using just 10 without a pattern.

Using int? n which matches nullable but cannot use when condition properly.

The pattern int n when n == 10 matches a non-null int with value 10 inside the nullable.

4fill in blank

hard

Fill both blanks to create a switch expression that returns a description for the shape object.

C Sharp (C#)

object shape = new Circle();
string description = shape switch
{
    [1] => "It's a circle",
    [2] => "It's a square",
    _ => "Unknown shape"
};

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ACircle c

BSquare s

CTriangle t

DRectangle r

Attempts:

3 left

💡 Hint

Common Mistakes

Using types that don't match the shape object.

Omitting the variable name after the type.

The patterns Circle c and Square s match objects of those types.

5fill in blank

hard

Fill all three blanks to create a switch expression that returns a message based on the input object type and value.

C Sharp (C#)

object input = 42;
string message = input switch
{
    [1] when [2] > 40 => "Large integer",
    [3] => "Not a large integer",
    _ => "Unknown"
};

Drag options to blanks, or click blank then click option'

Aint n

Bn

Cstring s

Ddouble d

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name in the when condition that is not declared in the pattern.

Using the wrong type patterns.

The first pattern matches an int and uses n in the condition. The second pattern matches a string.

Practice

1. What does pattern matching in a switch statement primarily help you do in C#?

easy

A. Check an object's type and properties in a clear way

B. Loop through collections more efficiently

C. Declare variables with less code

D. Handle exceptions automatically

Solution

1. Step 1: Understand pattern matching purpose

   Pattern matching in switch lets you test an object's type and properties clearly.

2. Step 2: Compare with other options

   Looping, variable declaration, and exception handling are unrelated to pattern matching in switch.

3. Final Answer:

   Check an object's type and properties in a clear way -> Option A

4. Quick Check:

   Pattern matching = type and property checks [OK]

Hint: Pattern matching checks types and conditions clearly [OK]

Common Mistakes:

• Confusing pattern matching with loops
• Thinking it handles exceptions
• Believing it declares variables automatically

2. Which of the following is the correct syntax to match an integer variable num equal to 10 using pattern matching in a switch expression?

easy

A. case int n when n == 10:

B. case int n == 10:

C. case int n => 10:

D. case int n is 10:

Solution

1. Step 1: Recall correct pattern matching syntax

   To match a value with a condition, use case Type variable when condition:.

2. Step 2: Check each option

   case int n when n == 10: uses when n == 10, which is correct. Others use invalid syntax.

3. Final Answer:

   case int n when n == 10: -> Option A

4. Quick Check:

   Use 'when' for conditions in pattern matching [OK]

Hint: Use 'when' keyword for conditions in switch patterns [OK]

Common Mistakes:

• Using '==' directly after case without 'when'
• Using '=>' or 'is' incorrectly in case
• Omitting the variable name

3. What will be the output of this C# code?

object obj = 42;
switch (obj)
{
    case int n when n > 40:
        Console.WriteLine("Greater than 40");
        break;
    case int n:
        Console.WriteLine("Integer");
        break;
    default:
        Console.WriteLine("Other");
        break;
}

medium

A. Integer

B. Other

C. Greater than 40

D. No output (compile error)

Solution

1. Step 1: Identify the object type and value

   obj is an integer with value 42.

2. Step 2: Evaluate switch cases in order

   First case matches int n when n > 40, which is true for 42, so prints "Greater than 40" and breaks.

3. Final Answer:

   Greater than 40 -> Option C

4. Quick Check:

   Pattern with 'when' matched first [OK]

Hint: Check cases top to bottom; first match runs [OK]

Common Mistakes:

• Ignoring the 'when' condition
• Assuming second case runs first
• Thinking default runs for int

4. Identify the error in this switch statement using pattern matching:

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

medium

A. Cannot use 'when' with string type

B. Missing colon ':' after case pattern

C. Missing parentheses around condition

D. Incorrect variable name in case

Solution

1. Step 1: Check switch case syntax

   Each case pattern must end with a colon ':' before the statements.

2. Step 2: Locate missing colon

   The case line lacks ':' after when s.Length > 3, causing syntax error.

3. Final Answer:

   Missing colon ':' after case pattern -> Option B

4. Quick Check:

   Case patterns need ':' after condition [OK]

Hint: Always put ':' after case pattern line [OK]

Common Mistakes:

• Forgetting ':' after case pattern
• Adding parentheses around 'when' condition
• Thinking 'when' can't be used with strings

5. Given a list of objects items containing integers and strings, how would you use pattern matching in a switch expression to return a new list of strings where:
- Integers greater than 10 become "Big number"
- Strings longer than 5 characters become "Long text"
- All others become "Other"?

Which code snippet correctly implements this?

hard

A. items.Select(item => item switch {
int n when n > 10: "Big number",
string s when s.Length > 5: "Long text",
_ => "Other"
}).ToList();

B. items.Select(item => switch (item) {
case int n if n > 10: "Big number";
case string s if s.Length > 5: "Long text";
default: "Other";
}).ToList();

C. items.Select(item => item switch {
int n if n > 10: "Big number",
string s if s.Length > 5: "Long text",
_ => "Other"
}).ToList();

D. items.Select(item => item switch {
int n when n > 10 => "Big number",
string s when s.Length > 5 => "Long text",
_ => "Other"
}).ToList();

Solution

1. Step 1: Understand switch expression syntax

   Switch expressions use '=>' for cases, and 'when' for conditions.

2. Step 2: Check each option's syntax

   items.Select(item => item switch { int n when n > 10 => "Big number", string s when s.Length > 5 => "Long text", _ => "Other" }).ToList(); uses correct 'item switch { case => result }' with 'when' and '=>'. Other options use invalid syntax ('switch' inside lambda or 'if' instead of 'when'). items.Select(item => item switch { int n when n > 10: "Big number", string s when s.Length > 5: "Long text", _ => "Other" }).ToList(); uses ':' instead of '=>', which is invalid in switch expressions.

3. Final Answer:

   items.Select(item => item switch { int n when n > 10 => "Big number", string s when s.Length > 5 => "Long text", _ => "Other" }).ToList(); -> Option D

4. Quick Check:

   Switch expressions use '=>' and 'when' [OK]

Hint: Use '=>' and 'when' in switch expressions for conditions [OK]

Common Mistakes:

• Using ':' instead of '=>' in switch expressions
• Using 'if' instead of 'when' for conditions
• Trying to put 'switch' keyword inside lambda