Expression-bodied methods in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an expression-bodied method in C#?

An expression-bodied method is a concise way to write methods using the => syntax to return a single expression instead of a full block with braces.

beginner

Rewrite this method using expression-bodied syntax:

int Square(int x) { return x * x; }

int Square(int x) => x * x;

beginner

Can expression-bodied methods have multiple statements inside?

No, expression-bodied methods can only have a single expression. For multiple statements, use the regular method body with braces.

intermediate

How do expression-bodied methods improve code readability?

They make simple methods shorter and clearer by removing unnecessary braces and return keywords, making the code easier to read and write.

intermediate

Which C# version introduced expression-bodied methods?

Expression-bodied methods were introduced in C# 6.0.

Which symbol is used to define an expression-bodied method in C#?

A ->

B =>=

C ::

D =>

Expression-bodied methods use the lambda arrow => to define the method body as a single expression.

Can an expression-bodied method contain multiple statements?

A Yes, with semicolons separating them

B No, only a single expression is allowed

C Yes, if enclosed in parentheses

D Only if marked async

Expression-bodied methods only allow a single expression, not multiple statements.

What is the benefit of using expression-bodied methods?

A They allow multiple return values

B They enable method overloading

C They make code shorter and more readable for simple methods

D They improve runtime performance

Expression-bodied methods simplify code by making simple methods shorter and easier to read.

Which C# version first introduced expression-bodied methods?

A C# 6.0

B C# 5.0

C C# 7.0

D C# 8.0

Expression-bodied methods were introduced in C# 6.0.

How would you convert this method to expression-bodied syntax?

string GetName() { return "Alice"; }

A string GetName() => "Alice";

B string GetName() => { return "Alice"; };

C string GetName() => return "Alice";

D string GetName() => { "Alice"; };

The correct expression-bodied syntax uses => followed by the expression without braces or return keyword.

Explain what expression-bodied methods are and when you would use them.

Think about how to write short methods more clearly.

Show how to convert a normal method with a return statement into an expression-bodied method.

Focus on replacing the method body with a single expression.

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