Immediate execution methods in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Count() on a filtered list

What is the output of this C# code using LINQ's immediate execution method Count()?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        int[] numbers = {1, 2, 3, 4, 5};
        int count = numbers.Where(n => n > 3).Count();
        Console.WriteLine(count);
    }
}

A 0

B 2

C 3

D 5

💡 Hint

Count() returns how many items match the condition immediately.

The Where clause filters numbers greater than 3: 4 and 5. Count() returns 2 immediately.

❓ Predict Output

intermediate

Result of ToList() on a query

What will be printed by this C# program using ToList() for immediate execution?

C Sharp (C#)

using System;
using System.Linq;
using System.Collections.Generic;

class Program {
    static void Main() {
        var words = new List<string> {"apple", "banana", "cherry"};
        var filtered = words.Where(w => w.Contains('a')).ToList();
        Console.WriteLine(filtered.Count);
    }
}

A 2

B 3

C 1

D 0

💡 Hint

ToList() creates a list immediately with all matching items.

Words containing 'a' are "apple" and "banana", so filtered list has 2 items.

❓ Predict Output

advanced

Output of First() with condition

What does this C# code print when using First() as an immediate execution method?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        int[] nums = {10, 20, 30, 40};
        int first = nums.Where(n => n > 15).First();
        Console.WriteLine(first);
    }
}

A 20

B 10

C 30

D Throws InvalidOperationException

💡 Hint

First() returns the first element that matches the condition immediately.

Numbers greater than 15 are 20, 30, 40. First() returns 20.

❓ Predict Output

advanced

Output of Single() with one matching element

What will this C# program print using Single() as an immediate execution method?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        int[] values = {5, 10, 15};
        int single = values.Single(v => v == 10);
        Console.WriteLine(single);
    }
}

A 15

B 5

C Throws InvalidOperationException

D 10

💡 Hint

Single() returns the only element matching the condition or throws if none or multiple.

Only 10 matches v == 10, so Single() returns 10.

❓ Predict Output

expert

Output of Count() after modifying source collection

What is the output of this C# program that uses Count() immediate execution after modifying the source array?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        int[] data = {1, 2, 3, 4};
        var query = data.Where(x => x > 2);
        data[2] = 10; // change 3 to 10
        int count = query.Count();
        Console.WriteLine(count);
    }
}

A 3

B 1

C 2

D 0

💡 Hint

Count() evaluates the query immediately using the current state of the data.

After changing data[2] to 10, elements > 2 are 10 and 4, so count is 2.