Expression-bodied lambdas in C Sharp (C#) - Mini Project: Build & Apply

Expression-bodied Lambdas in C#

📖 Scenario: You are working on a small program that processes a list of numbers. You want to use simple functions to perform calculations on these numbers.

🎯 Goal: Learn how to write expression-bodied lambda functions in C# to make your code shorter and easier to read.

📋 What You'll Learn

Create a list of integers

Create an expression-bodied lambda to double a number

Use the lambda to create a new list with doubled values

Print the new list

💡 Why This Matters

🌍 Real World

Expression-bodied lambdas are used to write short, clear functions for data processing, event handling, and callbacks in many C# applications.

💼 Career

Knowing how to write concise lambdas helps you write cleaner code and work efficiently in C# development jobs.

1

Create a list of integers

Create a list of integers called numbers with these exact values: 1, 2, 3, 4, 5

C Sharp (C#)

# Create the list called numbers with values 1, 2, 3, 4, 5
// Your code here

Hint

Use List<int> and initialize it with the values inside curly braces.

2

Create an expression-bodied lambda to double a number

Create an expression-bodied lambda called doubleNumber that takes an int parameter n and returns n * 2

C Sharp (C#)

using System.Collections.Generic;

List numbers = new List { 1, 2, 3, 4, 5 };

// Create the expression-bodied lambda doubleNumber here
// Your code here

Hint

Use Func<int, int> and the lambda arrow => with a single expression.

3

Use the lambda to create a new list with doubled values

Create a new list of integers called doubledNumbers by using numbers.ConvertAll with the doubleNumber lambda

C Sharp (C#)

using System;
using System.Collections.Generic;

List numbers = new List { 1, 2, 3, 4, 5 };

Func doubleNumber = n => n * 2;

// Create doubledNumbers list using numbers.ConvertAll and doubleNumber
// Your code here

Hint

Use ConvertAll method on the numbers list and pass doubleNumber as the converter.

4

Print the new list

Use a foreach loop to print each number in doubledNumbers on its own line

C Sharp (C#)

using System;
using System.Collections.Generic;

List numbers = new List { 1, 2, 3, 4, 5 };

Func doubleNumber = n => n * 2;

List doubledNumbers = numbers.ConvertAll(doubleNumber);

// Print each number in doubledNumbers using foreach
// Your code here

Hint

Use foreach (int num in doubledNumbers) and inside the loop use Console.WriteLine(num);.

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