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

Using Expression-Bodied Methods in C#

📖 Scenario: You are building a simple calculator class to perform basic math operations. You want to write clean and short methods using expression-bodied syntax.

🎯 Goal: Create a Calculator class with expression-bodied methods for addition, subtraction, multiplication, and division. Then use the class to calculate and display results.

📋 What You'll Learn

Create a class called Calculator

Add expression-bodied methods Add, Subtract, Multiply, and Divide

Each method takes two int parameters and returns an int

Use the methods to calculate results for given numbers

Print the results exactly as shown

💡 Why This Matters

🌍 Real World

Expression-bodied methods are used in real-world C# projects to write concise and readable code, especially for simple methods and properties.

💼 Career

Knowing expression-bodied methods helps you write clean code, which is valued in software development jobs and improves maintainability.

1

Create the Calculator class

Create a class called Calculator with no methods yet.

C Sharp (C#)

class Calculator
{
    // Your code here
}

Hint

Use the class keyword followed by the class name Calculator.

2

Add expression-bodied Add and Subtract methods

Inside the Calculator class, add two expression-bodied methods: int Add(int a, int b) => a + b; and int Subtract(int a, int b) => a - b;.

C Sharp (C#)

class Calculator
{
    // Add expression-bodied Add and Subtract methods here
}

Hint

Use the arrow => syntax to write short methods that return the result directly.

3

Add expression-bodied Multiply and Divide methods

Add two more expression-bodied methods inside Calculator: int Multiply(int a, int b) => a * b; and int Divide(int a, int b) => a / b;.

C Sharp (C#)

class Calculator
{
    public int Add(int a, int b) => a + b;
    public int Subtract(int a, int b) => a - b;
    // Add Multiply and Divide methods here
}

Hint

Remember to use the arrow => syntax for these methods as well.

4

Use Calculator methods and print results

Create a Calculator object called calc. Use it to calculate calc.Add(10, 5), calc.Subtract(10, 5), calc.Multiply(10, 5), and calc.Divide(10, 5). Print each result on its own line exactly as: Add: 15, Subtract: 5, Multiply: 50, Divide: 2.

C Sharp (C#)

class Calculator
{
    public int Add(int a, int b) => a + b;
    public int Subtract(int a, int b) => a - b;
    public int Multiply(int a, int b) => a * b;
    public int Divide(int a, int b) => a / b;
}

// Create Calculator object and print results here

Hint

Create an instance of Calculator and use Console.WriteLine with string interpolation to print results.

Practice

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

easy

A. To handle exceptions more efficiently

B. To declare variables with less code

C. To create classes without constructors

D. To write simple methods in a shorter and clearer way using the => syntax

Solution

1. Step 1: Understand expression-bodied methods

   Expression-bodied methods use the => symbol to return a single expression directly, making code shorter.

2. Step 2: Identify the purpose

   The main purpose is to simplify simple methods by writing them in one line with clear syntax.

3. Final Answer:

   To write simple methods in a shorter and clearer way using the => syntax -> Option D

4. Quick Check:

   Expression-bodied methods = shorter, clearer methods [OK]

Hint: Expression-bodied methods use => for short, single-expression methods [OK]

Common Mistakes:

• Confusing expression-bodied methods with variable declarations
• Thinking they handle exceptions
• Believing they create classes

2. Which of the following is the correct syntax for an expression-bodied method that returns the square of an integer n?

easy

A. public int Square(int n) => n * n;

B. public int Square(int n) { return n * n; }

C. public int Square(int n) => { return n * n; };

D. public int Square(int n) => return n * n;

Solution

1. Step 1: Recall expression-bodied method syntax

   Expression-bodied methods use => followed directly by the expression without braces or return keyword.

2. Step 2: Check each option

   public int Square(int n) => n * n; correctly uses => n * n; without braces or return. public int Square(int n) { return n * n; } uses normal method syntax. Options C and D have syntax errors.

3. Final Answer:

   public int Square(int n) => n * n; -> Option A

4. Quick Check:

   Correct syntax = public int Square(int n) => n * n; [OK]

Hint: Use => expression; without braces or return for expression-bodied methods [OK]

Common Mistakes:

• Adding braces {} around the expression
• Using return keyword with =>
• Missing semicolon at the end

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

class Program {
    static int Double(int x) => x * 2;
    static void Main() {
        Console.WriteLine(Double(5));
    }
}

medium

A. 5

B. 10

C. Syntax error

D. 0

Solution

1. Step 1: Understand the method Double

   The method Double takes an integer x and returns x multiplied by 2 using expression-bodied syntax.

2. Step 2: Calculate the output for Double(5)

   Double(5) returns 5 * 2 = 10, which is printed by Console.WriteLine.

3. Final Answer:

   10 -> Option B

4. Quick Check:

   Double(5) = 10 [OK]

Hint: Multiply input by 2 in expression-bodied method to get output [OK]

Common Mistakes:

• Confusing output with input value
• Expecting syntax error due to unfamiliar syntax
• Ignoring return value

4. Identify the error in the following expression-bodied method and choose the correct fix:

public int Add(int a, int b) => { return a + b; };

medium

A. Change => to =>> : public int Add(int a, int b) =>> a + b;

B. Add semicolon after return: public int Add(int a, int b) => { return a + b; };

C. Remove braces and return keyword: public int Add(int a, int b) => a + b;

D. No error, code is correct

Solution

1. Step 1: Analyze expression-bodied method syntax

   Expression-bodied methods must have a single expression after => without braces or return keyword.

2. Step 2: Identify the fix

   Remove braces and return keyword to fix syntax: public int Add(int a, int b) => a + b;

3. Final Answer:

   Remove braces and return keyword: public int Add(int a, int b) => a + b; -> Option C

4. Quick Check:

   Expression-bodied method = single expression after => [OK]

Hint: No braces or return with =>; just expression [OK]

Common Mistakes:

• Using braces {} with expression-bodied methods
• Including return keyword after =>
• Thinking =>> is valid syntax

5. You want to create an expression-bodied method IsEven that returns true if an integer is even, and false otherwise. Which of the following implementations is correct?

hard

A. public bool IsEven(int n) => n % 2 == 0;

B. public bool IsEven(int n) => { if (n % 2 == 0) return true; else return false; };

C. public bool IsEven(int n) => return n % 2 == 0;

D. public bool IsEven(int n) => n / 2 == 0;

Solution

1. Step 1: Understand the method goal

   The method should return true if n is even (n % 2 == 0), false otherwise.

2. Step 2: Check each option

   public bool IsEven(int n) => n % 2 == 0; correctly uses expression-bodied syntax with the expression n % 2 == 0. public bool IsEven(int n) => { if (n % 2 == 0) return true; else return false; }; uses braces and return, which is invalid for expression-bodied methods. public bool IsEven(int n) => return n % 2 == 0; incorrectly uses return keyword after =>. public bool IsEven(int n) => n / 2 == 0; incorrectly checks n / 2 == 0, which is wrong logic.

3. Final Answer:

   public bool IsEven(int n) => n % 2 == 0; -> Option A

4. Quick Check:

   IsEven uses n % 2 == 0 with => [OK]

Hint: Use expression n % 2 == 0 directly after => for boolean return [OK]

Common Mistakes:

• Using braces and return in expression-bodied methods
• Adding return keyword after =>
• Incorrect logic like n / 2 == 0