Func delegate type in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Func delegate example?

Consider the following C# code using a Func delegate. What will be printed to the console?

C Sharp (C#)

Func<int, int, int> multiply = (x, y) => x * y;
Console.WriteLine(multiply(3, 4));

A 12

B Error at compile time

C 34

D 7

💡 Hint

Func delegates can take parameters and return a value. Here it multiplies two integers.

The Func delegate takes two integers and returns their product. multiply(3,4) returns 12.

❓ Predict Output

intermediate

What is the output of this Func with no parameters?

Look at this C# code using a Func delegate with no parameters. What will it print?

C Sharp (C#)

Func<string> greet = () => "Hello World!";
Console.WriteLine(greet());

A Error: Func must have parameters

B greet

C Hello World!

D null

💡 Hint

Func can have zero parameters and return a value.

The Func delegate here takes no parameters and returns the string "Hello World!". Calling greet() prints that string.

🔧 Debug

advanced

What error does this Func delegate code produce?

Examine this C# code snippet. What error will it cause when compiled?

C Sharp (C#)

Func<int, int> square = x => x * x;
int result = square();

A Output: 1

B Runtime error: NullReferenceException

C Output: 0

D Compile-time error: No overload for 'square' takes 0 arguments

💡 Hint

Check how many arguments the Func delegate expects.

The Func delegate expects one integer argument. Calling square() with no arguments causes a compile-time error.

🧠 Conceptual

advanced

How many parameters can a Func delegate have at most?

In C#, what is the maximum number of input parameters a Func delegate can have?

A 16

B 8

C 4

D No limit

💡 Hint

Check the official Microsoft documentation for Func delegates.

Func delegates can have up to 16 input parameters, with the last type parameter being the return type.

❓ Predict Output

expert

What is the output of this nested Func delegate example?

Analyze this C# code using nested Func delegates. What will be printed?

C Sharp (C#)

Func<int, Func<int, int>> add = x => y => x + y;
var addFive = add(5);
Console.WriteLine(addFive(10));

A 510

B 15

C 5

D Compile-time error

💡 Hint

The outer Func returns another Func that adds two numbers.

The outer Func takes x and returns a Func that takes y and returns x + y. add(5) returns a Func adding 5 to its input. addFive(10) returns 15.

Practice

1. What is the main purpose of the Func delegate type in C#?

easy

A. To store methods that return a value

B. To store methods that do not return a value

C. To create variables of any data type

D. To define classes

Solution

1. Step 1: Understand what Func represents

   Func is a delegate type designed to hold references to methods that return a value.

2. Step 2: Differentiate from other delegates

   Unlike Action, which stores methods without return values, Func always returns a value.

3. Final Answer:

   To store methods that return a value -> Option A

4. Quick Check:

   Func stores methods with return values = C [OK]

Hint: Remember: Func always returns a value, Action does not [OK]

Common Mistakes:

• Confusing Func with Action delegate
• Thinking Func can store void methods
• Assuming Func defines classes

2. Which of the following is the correct syntax to declare a Func delegate that takes two integers and returns an integer?

easy

A. Func add = (x, y) => x + y;

B. Func add = (x, y) => x + y;

C. Func<int> add = (x, y) => x + y;

D. Func add = (x, y) => x + y;

Solution

1. Step 1: Understand Func generic parameters

   The last type parameter is the return type; previous ones are input types. For two integers input and one integer output, use Func.

2. Step 2: Check lambda expression matches parameters

   The lambda (x, y) => x + y takes two inputs and returns their sum, matching the delegate.

3. Final Answer:

   Func<int, int, int> add = (x, y) => x + y; -> Option B

4. Quick Check:

   Two inputs + one output = Func<int, int, int> [OK]

Hint: Count inputs, last type is output in Func<> [OK]

Common Mistakes:

• Using wrong number of generic parameters
• Mixing input and output types order
• Incorrect lambda parameter count

3. What is the output of the following code?

Func<int, int, int> multiply = (a, b) => a * b;
int result = multiply(3, 4);
Console.WriteLine(result);

medium

A. 12

B. 7

C. 34

D. Error

Solution

1. Step 1: Understand the Func delegate and lambda

   The delegate multiply takes two integers and returns their product.

2. Step 2: Calculate the result of multiply(3, 4)

   3 multiplied by 4 equals 12.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   3 * 4 = 12 [OK]

Hint: Multiply inputs as lambda defines [OK]

Common Mistakes:

• Adding instead of multiplying
• Concatenating numbers as strings
• Expecting syntax error

4. Identify the error in this code snippet:

Func<int, int> square = x => x * x;
int result = square(5, 2);
Console.WriteLine(result);

medium

A. Syntax error in lambda expression

B. Missing return statement in lambda

C. Incorrect delegate type for lambda

D. Too many arguments passed to the Func delegate

Solution

1. Step 1: Check Func delegate signature

   Func<int, int> expects one integer input and returns an integer.

2. Step 2: Check method call arguments

   The call square(5, 2) passes two arguments, but the delegate expects only one.

3. Final Answer:

   Too many arguments passed to the Func delegate -> Option D

4. Quick Check:

   One input expected, two given = error [OK]

Hint: Match argument count to Func input count [OK]

Common Mistakes:

• Passing wrong number of arguments
• Confusing input and output types
• Assuming lambda needs explicit return

5. You want to create a Func delegate that takes a string and returns its length only if the string is not null or empty; otherwise, it returns zero. Which of the following implementations correctly achieves this?

hard

A. Func lengthFunc = s => { if (s == null) return 0; else return s.Length; };

B. Func lengthFunc = s => s.Length;

C. Func lengthFunc = s => string.IsNullOrEmpty(s) ? 0 : s.Length;

D. Func lengthFunc = s => s == "" ? s.Length : 0;

Solution

1. Step 1: Understand the requirement

   The function must return 0 if the string is null or empty, else return its length.

2. Step 2: Analyze each option

   Func lengthFunc = s => string.IsNullOrEmpty(s) ? 0 : s.Length; uses string.IsNullOrEmpty to check both conditions and returns 0 or length accordingly, which is correct. Func lengthFunc = s => s.Length; does not check for null or empty and may throw an error. Func lengthFunc = s => { if (s == null) return 0; else return s.Length; }; checks only for null, not empty. Func lengthFunc = s => s == "" ? s.Length : 0; returns length only if string is empty, which is opposite.

3. Final Answer:

   Func<string, int> lengthFunc = s => string.IsNullOrEmpty(s) ? 0 : s.Length; -> Option C

4. Quick Check:

   Check null or empty with IsNullOrEmpty = Func lengthFunc = s => string.IsNullOrEmpty(s) ? 0 : s.Length; [OK]

Hint: Use string.IsNullOrEmpty to check safely [OK]

Common Mistakes:

• Not checking empty string
• Only checking null but not empty
• Returning wrong value for empty string