Expression-bodied lambdas in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an expression-bodied lambda that adds two numbers.

C Sharp (C#)

Func<int, int, int> add = (x, y) => x [1] y;

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' will subtract the numbers.

Using '*' or '/' will multiply or divide instead of adding.

The expression-bodied lambda uses the '+' operator to add x and y.

2fill in blank

medium

Complete the code to create an expression-bodied lambda that returns the square of a number.

C Sharp (C#)

Func<int, int> square = x => x [1] x;

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' will add the number to itself, not square it.

Using '-' or '/' will not produce the square.

The expression-bodied lambda uses the '*' operator to multiply x by itself, returning the square.

3fill in blank

hard

Fix the error in the expression-bodied lambda that returns true if a number is even.

C Sharp (C#)

Func<int, bool> isEven = x => x [1] 2 == 0;

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

A+

B%

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' or '-' will not check for evenness.

Using '/' will give the quotient, not the remainder.

The '%' operator gives the remainder. If x % 2 equals 0, x is even.

4fill in blank

hard

Fill both blanks to create an expression-bodied lambda that returns true if a string is longer than 5 characters.

C Sharp (C#)

Func<string, bool> isLong = s => s.[1] > [2];

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

ALength

B5

CCount

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using Count instead of Length for strings.

Comparing to 10 instead of 5.

The lambda uses the Length property to get the string length and compares it to 5.

5fill in blank

hard

Fill all three blanks to create an expression-bodied lambda that returns a dictionary with keys as uppercase strings and values as their lengths.

C Sharp (C#)

var result = [1].ToDictionary([2] => [2].ToUpper(), [3] => [3].Length);

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

Awords

Bword

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Using 'list' instead of the actual collection name.

The lambda uses the list 'words' and the parameter 'word' to create a dictionary with uppercase keys and length values.

Practice

1. What is the main purpose of using an expression-bodied lambda in C#?

easy

A. To write a short function with a single expression without braces or return keyword

B. To declare a variable with a complex type

C. To create a class with multiple methods

D. To handle exceptions in a concise way

Solution

1. Step 1: Understand expression-bodied lambda syntax

   Expression-bodied lambdas use the => operator followed by a single expression, simplifying function syntax.

2. Step 2: Identify the purpose

   This syntax is used to write short functions without braces or explicit return statements.

3. Final Answer:

   To write a short function with a single expression without braces or return keyword -> Option A

4. Quick Check:

   Expression-bodied lambda = short single-expression function [OK]

Hint: Remember: expression-bodied lambdas simplify single-expression functions [OK]

Common Mistakes:

• Confusing with variable declarations
• Thinking it creates classes or handles exceptions
• Assuming it requires braces and return keyword

2. Which of the following is the correct syntax for an expression-bodied lambda that adds two integers a and b?

easy

A. (a, b) => a + b

B. (a, b) => a + b;

C. (a, b) => { return a + b; }

D. (a, b) => { a + b }

Solution

1. Step 1: Identify expression-bodied lambda syntax

   Expression-bodied lambdas use => followed by a single expression without braces or return keyword.

2. Step 2: Check each option

   (a, b) => a + b correctly uses (a, b) => a + b without braces or return. (a, b) => { return a + b; } uses braces and return (not expression-bodied). (a, b) => a + b; has a semicolon after expression (not needed). (a, b) => { a + b } uses braces without return (invalid).

3. Final Answer:

   (a, b) => a + b -> Option A

4. Quick Check:

   Expression-bodied lambda syntax = (params) => expression [OK]

Hint: No braces or return keyword in expression-bodied lambdas [OK]

Common Mistakes:

• Adding braces and return keyword
• Including semicolon after expression
• Using braces without return keyword

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

Func<int, int> square = x => x * x;
Console.WriteLine(square(4));

medium

A. 8

B. 4

C. 16

D. Compilation error

Solution

1. Step 1: Understand the lambda function

   The lambda expression x => x * x defines a function that returns the square of x.

2. Step 2: Evaluate the function call

   Calling square(4) computes 4 * 4 = 16.

3. Final Answer:

   16 -> Option C

4. Quick Check:

   4 squared = 16 [OK]

Hint: Multiply input by itself to get square [OK]

Common Mistakes:

• Confusing output with input
• Expecting compilation error
• Misreading the lambda expression

4. Identify the error in the following expression-bodied lambda:

Func<int, int> increment = x => { x + 1; };

medium

A. Semicolon after expression is invalid

B. Braces are not allowed in expression-bodied lambdas

C. Lambda must have two parameters

D. Missing return keyword inside braces

Solution

1. Step 1: Analyze the lambda syntax

   The lambda uses braces, so it must have an explicit return statement to return a value.

2. Step 2: Identify the missing return

   Inside braces, the expression x + 1 is evaluated but not returned, causing a compile error.

3. Final Answer:

   Missing return keyword inside braces -> Option D

4. Quick Check:

   Braces require return keyword [OK]

Hint: Use return inside braces or remove braces for expression-bodied lambda [OK]

Common Mistakes:

• Assuming braces are disallowed
• Thinking semicolon after expression is invalid
• Expecting multiple parameters

5. Given a list of integers, which expression-bodied lambda correctly filters out even numbers and returns their squares?

var numbers = new List<int> {1, 2, 3, 4, 5};
var result = numbers.Where( /* lambda here */ ).Select(x => x * x).ToList();

hard

A. x => x % 2 == 0

B. x => x % 2 != 0

C. x => { return x % 2 != 0; }

D. x => { x % 2 != 0; }

Solution

1. Step 1: Understand filtering condition

   We want to keep odd numbers, so the condition is x % 2 != 0.

2. Step 2: Choose correct lambda syntax

   x => x % 2 != 0 uses expression-bodied lambda without braces, correctly returning the condition. x => x % 2 == 0 keeps even numbers (wrong). x => { return x % 2 != 0; } uses braces with return (valid but not expression-bodied). x => { x % 2 != 0; } uses braces without return (invalid).

3. Final Answer:

   x => x % 2 != 0 -> Option B

4. Quick Check:

   Filter odds with expression-bodied lambda [OK]

Hint: No braces and return for expression-bodied lambdas [OK]

Common Mistakes:

• Using braces without return
• Choosing wrong condition for filtering
• Mixing expression-bodied with block-bodied syntax