Expression-bodied methods in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of expression-bodied method with arithmetic

What is the output of this C# code using an expression-bodied method?

C Sharp (C#)

class Calculator {
    public int Double(int x) => x * 2;
}

var calc = new Calculator();
System.Console.WriteLine(calc.Double(5));

A 25

B 5

C 10

D Compilation error

💡 Hint

Look at how the method returns the value directly using the expression-bodied syntax.

The method Double returns x multiplied by 2. For input 5, output is 10.

❓ Predict Output

intermediate

Expression-bodied property output

What will be printed by this C# program using an expression-bodied property?

C Sharp (C#)

class Person {
    public string Name { get; }
    public Person(string name) => Name = name;
    public string Greeting => $"Hello, {Name}!";
}

var p = new Person("Anna");
System.Console.WriteLine(p.Greeting);

A Hello, Anna!

B Hello, !

C Anna

D Compilation error

💡 Hint

The Greeting property uses expression-bodied syntax to return a formatted string.

The Greeting property returns "Hello, " plus the Name property value, which is "Anna".

❓ Predict Output

advanced

Expression-bodied method with conditional expression

What is the output of this C# code using an expression-bodied method with a conditional operator?

C Sharp (C#)

class NumberCheck {
    public string Check(int n) => n % 2 == 0 ? "Even" : "Odd";
}

var checker = new NumberCheck();
System.Console.WriteLine(checker.Check(7));

A 7

B Odd

C Even

D Compilation error

💡 Hint

The method returns "Even" if the number is divisible by 2, otherwise "Odd".

7 is not divisible by 2, so the method returns "Odd".

❓ Predict Output

advanced

Expression-bodied method with tuple return

What is the output of this C# code that uses an expression-bodied method returning a tuple?

C Sharp (C#)

class Point {
    public int X { get; }
    public int Y { get; }
    public Point(int x, int y) => (X, Y) = (x, y);
    public (int, int) GetCoordinates() => (X, Y);
}

var pt = new Point(3, 4);
var coords = pt.GetCoordinates();
System.Console.WriteLine($"({coords.Item1}, {coords.Item2})");

A Compilation error

B (4, 3)

C (0, 0)

D (3, 4)

💡 Hint

The method returns the tuple of X and Y properties directly.

The GetCoordinates method returns (3, 4), so the output is (3, 4).

❓ Predict Output

expert

Expression-bodied method with pattern matching and switch expression

What is the output of this C# code using an expression-bodied method with a switch expression and pattern matching?

C Sharp (C#)

class Shape {
    public string Type { get; }
    public double Size { get; }
    public Shape(string type, double size) => (Type, Size) = (type, size);
    public string Describe() => Type switch {
        "Circle" when Size > 0 => $"Circle with radius {Size}",
        "Square" when Size > 0 => $"Square with side {Size}",
        _ => "Unknown shape"
    };
}

var shape = new Shape("Circle", 5);
System.Console.WriteLine(shape.Describe());

A Circle with radius 5

B Square with side 5

C Unknown shape

D Compilation error

💡 Hint

The switch expression matches the Type and checks the Size condition.

The Type is "Circle" and Size is 5 > 0, so it returns "Circle with radius 5".

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