Switch expressions with patterns in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the correct string for the number using a switch expression.

C Sharp (C#)

string result = number switch [1];

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

A< 1 => "One", 2 => "Two", _ => "Other" >

B( 1 => "One", 2 => "Two", _ => "Other" )

C[ 1 => "One", 2 => "Two", _ => "Other" ]

D{ 1 => "One", 2 => "Two", _ => "Other" }

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or brackets instead of curly braces for switch expression.

Forgetting the underscore (_) as the default case.

The switch expression in C# uses curly braces with pattern cases inside.

2fill in blank

medium

Complete the switch expression to return "Positive" for numbers greater than zero.

C Sharp (C#)

string result = number switch {
    > 0 => "Positive",
    0 => "Zero",
    [1] => "Negative"
};

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

A< 0

B> 0

C== 0

D>= 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>= 0' which overlaps with zero and positive cases.

Using '== 0' which duplicates the zero case.

The pattern '< 0' matches negative numbers in the switch expression.

3fill in blank

hard

Fix the error in the switch expression to correctly handle strings starting with 'A'.

C Sharp (C#)

string result = input switch {
    [1] => "Starts with A",
    _ => "Other"
};

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

Astring s => s.StartsWith("A")

Bstring s when s.StartsWith("A")

Cstring s if s.StartsWith("A")

Dstring s where s.StartsWith("A")

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=>' instead of 'when' for conditions.

Using 'if' or 'where' which are invalid in this context.

The correct syntax for pattern matching with a condition is 'type variable when condition'.

4fill in blank

hard

Fill both blanks to return the correct description for the shape using switch expression with type patterns.

C Sharp (C#)

string description = shape switch {
    [1] => "Circle with radius " + c.Radius,
    [2] => "Rectangle with width " + r.Width + " and height " + r.Height,
    _ => "Unknown shape"
};

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

ACircle c

BRectangle c

CRectangle r

DCircle r

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing variable names and types incorrectly.

Using the wrong variable name for the shape type.

Use type patterns with variable names matching the properties used in the expressions.

5fill in blank

hard

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

C Sharp (C#)

string message = obj switch {
    [1] when i > 0 => "Positive integer",
    [2] when s.Length == 0 => "Empty string",
    [3] => "Other"
};

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

Aint i

Bstring s

C_

Ddouble d

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or types in patterns.

Not using '_' for the default case.

Use type patterns with variable names for conditions and '_' as the default case.

Practice

1. What does a switch expression with patterns in C# primarily help you do?

easy

A. Create loops that run a fixed number of times

B. Declare variables with dynamic types

C. Match values and types cleanly without long if-else chains

D. Handle exceptions in asynchronous code

Solution

1. Step 1: Understand switch expressions

   Switch expressions allow matching on values or types in a concise way.

2. Step 2: Compare with if-else chains

   They replace long if-else chains with clearer, more readable code.

3. Final Answer:

   Match values and types cleanly without long if-else chains -> Option C

4. Quick Check:

   Switch expressions = clean matching [OK]

Hint: Switch expressions simplify matching values and types [OK]

Common Mistakes:

• Confusing switch expressions with loops
• Thinking switch expressions handle exceptions
• Believing switch expressions declare variables

2. Which of the following is the correct syntax for a switch expression with a type pattern in C#?

easy

A. var result = obj switch { int i => i * 2, string s => s.Length, _ => 0 };

B. var result = switch obj { int i => i * 2, string s => s.Length, _ => 0 };

C. var result = obj { int i => i * 2, string s => s.Length, _ => 0 } switch;

D. var result = obj switch (int i => i * 2, string s => s.Length, _ => 0);

Solution

1. Step 1: Identify correct switch expression syntax

   The switch expression syntax is: variable switch { pattern => result, ... }.

2. Step 2: Match options to syntax

   var result = obj switch { int i => i * 2, string s => s.Length, _ => 0 }; matches this syntax exactly with type patterns and a discard pattern.

3. Final Answer:

   var result = obj switch { int i => i * 2, string s => s.Length, _ => 0 }; -> Option A

4. Quick Check:

   Correct switch expression syntax = var result = obj switch { int i => i * 2, string s => s.Length, _ => 0 }; [OK]

Hint: Remember: variable switch { patterns } is correct syntax [OK]

Common Mistakes:

• Placing switch before the variable
• Using parentheses instead of braces
• Misplacing the switch keyword

3. What is the output of the following C# code?

object value = 5;
string result = value switch
{
  int i when i > 0 => "Positive integer",
  int i when i < 0 => "Negative integer",
  string s => "String",
  _ => "Unknown"
};
Console.WriteLine(result);

medium

A. Negative integer

B. Positive integer

C. String

D. Unknown

Solution

1. Step 1: Analyze the switch expression input

   The variable 'value' is an object holding the integer 5.

2. Step 2: Match patterns in order

   First pattern matches int i when i > 0, which is true for 5, so result is "Positive integer".

3. Final Answer:

   Positive integer -> Option B

4. Quick Check:

   5 > 0 matches first pattern [OK]

Hint: Check pattern order and conditions carefully [OK]

Common Mistakes:

• Ignoring the 'when' condition
• Assuming string pattern matches first
• Choosing default case incorrectly

4. Identify the error in this switch expression code snippet:

object obj = "hello";
var output = obj switch
{
  int i => i.ToString(),
  string s => s.ToUpper(),
  default => "none"
};

medium

A. Patterns must be in parentheses

B. Missing semicolon after switch expression

C. Cannot switch on object type

D. Using 'default' instead of '_' for discard pattern

Solution

1. Step 1: Check switch expression patterns

   In C# switch expressions, the discard pattern uses '_' not 'default'.

2. Step 2: Identify the incorrect pattern usage

   The code uses 'default' which causes a syntax error; it should be '_'.

3. Final Answer:

   Using 'default' instead of '_' for discard pattern -> Option D

4. Quick Check:

   Discard pattern = '_' not 'default' [OK]

Hint: Use '_' for default case in switch expressions [OK]

Common Mistakes:

• Using 'default' keyword in switch expressions
• Confusing switch statements with switch expressions
• Forgetting to end statements with semicolon

5. Given a list of objects, write a switch expression that returns:
- "Number" if the object is an int or double
- "Text" if the object is a non-empty string
- "Empty" if the object is an empty string
- "Other" for anything else

Which of the following switch expressions correctly implements this logic?

hard

A. obj switch { int _ or double _ => "Number", string s when s.Length == 0 => "Empty", string s when s.Length > 0 => "Text", _ => "Other" }

B. obj switch { int or double => "Number", string s when s == "" => "Empty", string s when s != "" => "Text", _ => "Other" }

C. obj switch { int or double => "Number", string s when s.Length > 0 => "Text", string s when s.Length == 0 => "Empty", _ => "Other" }

D. obj switch { int or double => "Number", string s when s != "" => "Text", string s when s == "" => "Empty", _ => "Other" }

Solution

1. Step 1: Understand type patterns and conditions

   We must match int or double first, then string with length checks for empty/non-empty.

2. Step 2: Check order and conditions

   obj switch { int _ or double _ => "Number", string s when s.Length == 0 => "Empty", string s when s.Length > 0 => "Text", _ => "Other" } correctly checks int or double, then string with Length == 0 for "Empty", then Length > 0 for "Text", then default.

3. Final Answer:

   obj switch { int _ or double _ => "Number", string s when s.Length == 0 => "Empty", string s when s.Length > 0 => "Text", _ => "Other" } -> Option A

4. Quick Check:

   Order and conditions matter in switch patterns [OK]

Hint: Order patterns from specific to general, check string length for empty [OK]

Common Mistakes:

• Using 'or' incorrectly without parentheses
• Checking string emptiness with == "" instead of Length
• Placing empty string check after non-empty