Lambda expression syntax in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple lambda expression

What is the output of this C# code snippet?

C Sharp (C#)

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

A Compilation error

B 25

C 10

D 5

💡 Hint

The lambda takes an integer and returns its square.

The lambda expression x => x * x takes an integer x and returns x multiplied by itself. So square(5) returns 25.

❓ Predict Output

intermediate

Lambda with multiple parameters and statement body

What will this code print?

C Sharp (C#)

Func<int, int, int> addAndMultiply = (a, b) => {
    int sum = a + b;
    return sum * 2;
};
Console.WriteLine(addAndMultiply(3, 4));

A 14

B 7

C 12

D Compilation error

💡 Hint

The lambda sums two numbers and then doubles the result.

The lambda adds 3 and 4 to get 7, then multiplies by 2 to get 14.

❓ Predict Output

advanced

Lambda capturing outer variable

What is the output of this code?

C Sharp (C#)

int factor = 3;
Func<int, int> multiply = x => x * factor;
factor = 5;
Console.WriteLine(multiply(4));

A Compilation error

B 15

C 12

D 20

💡 Hint

Lambdas capture variables by reference, not by value.

The lambda captures 'factor' by reference. Since 'factor' is changed to 5 before calling multiply(4), the output is 4 * 5 = 20.

❓ Predict Output

advanced

Lambda with incorrect syntax

Which option will cause a compilation error?

C Sharp (C#)

Func<int, int> f = x => x * 2;

A Func<int, int> f = (x) => x * 2;

B Func<int, int> f = x => { return x * 2; };

C Func<int, int> f = x => { x * 2; };

D Func<int, int> f = (int x) => x * 2;

💡 Hint

Check if the lambda body returns a value properly.

Option C has a block body but no return statement, so it does not return a value, causing a compilation error.

🧠 Conceptual

expert

Understanding lambda expression type inference

Given the code below, what is the inferred delegate type of the lambda expression?

C Sharp (C#)

var list = new List<int> {1, 2, 3};
var result = list.Select(x => x.ToString());

A Func<int, string>

B Action<int>

C Predicate<int>

D Func<string, int>

💡 Hint

Select expects a function that takes an int and returns a string.

The Select method expects a Func. Here TSource is int and TResult is string, so the lambda is Func.