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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an expression-bodied method that returns the square of a number.

C Sharp (C#)

public int Square(int 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 '+' instead of '*' will add the number to x instead of squaring.

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

The expression-bodied method uses the multiplication operator '*' to return the square of x.

2fill in blank

medium

Complete the expression-bodied method to return the length of a string parameter.

C Sharp (C#)

public int GetLength(string s) => s.[1];

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

ALength

BLength()

CCount

DSize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Length()' causes a syntax error because Length is a property, not a method.

Using 'Count' or 'Size' are not valid string properties in C#.

The Length property returns the number of characters in the string.

3fill in blank

hard

Fix the error in the expression-bodied method that returns the uppercase version of a string.

C Sharp (C#)

public string ToUpperCase(string s) => s.[1]();

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

AToUpper

Btoupper

Ctouppercase

DUpperCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'toupper' causes a compile error.

Using 'touppercase' or 'UpperCase' are not valid method names.

The correct method name is 'ToUpper' with capital T and U.

4fill in blank

hard

Fill both blanks to create an expression-bodied method that returns true if a number is even.

C Sharp (C#)

public bool IsEven(int num) => num [1] 2 [2] 0;

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

A%

B==

C!=

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '/' instead of '%' will not give the remainder.

Using '!=' instead of '==' will return true for odd numbers.

The method uses the modulus operator '%' to get the remainder and checks if it equals zero with '=='.

5fill in blank

hard

Fill all three blanks to create an expression-bodied method that returns a dictionary with words as keys and their lengths as values for words longer than 3 characters.

C Sharp (C#)

public Dictionary<string, int> WordLengths(List<string> words) => words.Where(w => w.[1] > [2]).ToDictionary(w => w, w => w.[3]);

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

ALength

B3

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Count' instead of 'Length' for strings causes errors.

Using a number other than 3 changes the filter condition.

The method filters words with Length > 3 and creates a dictionary with word lengths using the Length property.

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