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

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Predicate delegate example?

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

C Sharp (C#)

using System;

class Program {
    static void Main() {
        Predicate<int> isEven = x => x % 2 == 0;
        Console.WriteLine(isEven(10));
        Console.WriteLine(isEven(7));
    }
}

A True\nFalse

B False\nTrue

C 10\n7

D Compilation error

💡 Hint

Predicate returns a boolean indicating if the condition is met.

The Predicate delegate checks if the number is even. 10 is even, so True; 7 is odd, so False.

❓ Predict Output

intermediate

What does this Predicate delegate filter produce?

Given the following code, what is the output of the filtered list printed?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> numbers = new() {1, 2, 3, 4, 5};
        Predicate<int> isGreaterThanThree = n => n > 3;
        List<int> filtered = numbers.FindAll(isGreaterThanThree);
        foreach (var num in filtered) {
            Console.Write(num + " ");
        }
    }
}

A 3 4 5

B 1 2 3

C 4 5

D Compilation error

💡 Hint

Predicate filters elements where the condition is true.

Only numbers greater than 3 are included: 4 and 5.

❓ Predict Output

advanced

What is the output of this Predicate delegate with method group?

Analyze the code below. What will be printed when running this program?

C Sharp (C#)

using System;

class Program {
    static bool IsPositive(int x) => x > 0;

    static void Main() {
        Predicate<int> check = IsPositive;
        Console.WriteLine(check(-1));
        Console.WriteLine(check(0));
        Console.WriteLine(check(5));
    }
}

A True\nFalse\nTrue

B False\nFalse\nTrue

C False\nTrue\nTrue

D Compilation error

💡 Hint

The method returns true only if the number is greater than zero.

Negative and zero are not positive, so False; 5 is positive, so True.

❓ Predict Output

advanced

What error does this Predicate delegate code produce?

What error will occur when compiling or running this code?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        Predicate<string> isLong = s => s.Length > 5;
        Console.WriteLine(isLong(null));
    }
}

A System.NullReferenceException at runtime

B Compilation error: cannot convert lambda

C Output: False

D Output: True

💡 Hint

Calling Length on null causes an error.

The lambda tries to access Length of null, causing a NullReferenceException at runtime.

🧠 Conceptual

expert

How many items are in the resulting list after applying this Predicate?

Given the code below, how many integers remain in the list after filtering with the Predicate?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> nums = new() { -2, -1, 0, 1, 2, 3 };
        Predicate<int> pred = x => x * x > 1;
        List<int> result = nums.FindAll(pred);
        Console.WriteLine(result.Count);
    }
}

A 6

B 4

C 5

D 3

💡 Hint

Check which numbers squared are greater than 1.

Numbers with squares > 1 are -2(4), -1(1), 0(0), 1(1), 2(4), 3(9). Only -2, 2, 3 satisfy x*x > 1, but -1 and 1 do not (1 is not > 1). So count is 3.