Task and Task of T types in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple Task returning a string

What is the output of this C# program when run?

C Sharp (C#)

using System;
using System.Threading.Tasks;

class Program {
    static async Task Main() {
        Task<string> task = Task.FromResult("Hello World");
        string result = await task;
        Console.WriteLine(result);
    }
}

A Hello World

B Task`1

C System.Threading.Tasks.Task

D Compilation error

💡 Hint

Remember that Task.FromResult creates a completed Task with the given result.

The Task.FromResult method returns a completed Task with the specified result. Awaiting it returns the string "Hello World", which is printed.

❓ Predict Output

intermediate

Value of Task after delay

What will be the output of this program?

C Sharp (C#)

using System;
using System.Threading.Tasks;

class Program {
    static async Task Main() {
        Task<int> task = GetNumberAsync();
        int value = await task;
        Console.WriteLine(value);
    }

    static async Task<int> GetNumberAsync() {
        await Task.Delay(100);
        return 42;
    }
}

A Task`1

B 0

C 42

D Runtime exception

💡 Hint

The method returns 42 after a short delay.

The async method GetNumberAsync returns 42 after awaiting a delay. Awaiting the Task returns 42, which is printed.

❓ Predict Output

advanced

What happens when awaiting a non-generic Task?

Consider this code snippet. What is printed when it runs?

C Sharp (C#)

using System;
using System.Threading.Tasks;

class Program {
    static async Task Main() {
        Task task = Task.Delay(50);
        await task;
        Console.WriteLine("Done");
    }
}

A Done

B Task

C Compilation error

D Runtime exception

💡 Hint

Awaiting a Task waits for its completion but returns no value.

Awaiting a non-generic Task waits for it to complete. After the delay, "Done" is printed.

🧠 Conceptual

advanced

Difference between Task and Task

Which statement correctly describes the difference between Task and Task in C#?

A Task<T> is used only for synchronous operations, Task only for asynchronous.

B Task represents an operation that returns no value, while Task<T> represents an operation that returns a value of type T.

C Task<T> can only be awaited, Task cannot be awaited.

D Task and Task<T> are identical and interchangeable.

💡 Hint

Think about whether the operation returns a result or not.

Task is for operations that do not return a value. Task returns a value of type T when awaited.

🔧 Debug

expert

Identify the runtime error in this Task usage

What error will this code produce when run?

C Sharp (C#)

using System;
using System.Threading.Tasks;

class Program {
    static void Main() {
        Task<int> task = Task.Run(() => 10 / 0);
        Console.WriteLine(task.Result);
    }
}

A No error, prints 0

B System.DivideByZeroException

C Compilation error

D System.AggregateException

💡 Hint

Exceptions inside Tasks are wrapped when accessing Result.

The division by zero inside the Task causes a DivideByZeroException, but accessing task.Result throws an AggregateException wrapping it.

Practice

1. What is the main difference between Task and Task<T> in C#?

easy

A. Task does not return a value, Task<T> returns a value of type T.

B. Task runs synchronously, Task<T> runs asynchronously.

C. Task is used only for UI threads, Task<T> for background threads.

D. Task can return multiple values, Task<T> returns only one.

Solution

1. Step 1: Understand Task behavior

   Task represents an asynchronous operation that does not return a result.

2. Step 2: Understand Task<T> behavior

   Task<T> represents an asynchronous operation that returns a value of type T when it completes.

3. Final Answer:

   Task does not return a value, Task<T> returns a value of type T. -> Option A

4. Quick Check:

   Return value presence = Task does not return a value, Task<T> returns a value of type T. [OK]

Hint: Remember: Task = no result, Task<T> = returns result [OK]

Common Mistakes:

• Thinking Task runs synchronously
• Confusing Task<T> with multiple return values
• Assuming Task is only for UI threads

2. Which of the following is the correct way to declare a Task<int> that returns the number 5 asynchronously?

easy

A. Task<int> t = Task.Run(() => 5);

B. Task<int> t = new Task<int>(5);

C. Task<int> t = Task<int>.Run(5);

D. Task<int> t = Task.Run<int>(5);

Solution

1. Step 1: Check correct Task<T> creation syntax

   Use Task.Run(() => value) to create and start a task returning a value.

2. Step 2: Validate each option

   Task<int> t = Task.Run(() => 5); uses Task.Run(() => 5), which is correct. Options A, B, and C use invalid constructors or methods.

3. Final Answer:

   Task<int> t = Task.Run(() => 5); -> Option A

4. Quick Check:

   Correct Task creation syntax = Task<int> t = Task.Run(() => 5); [OK]

Hint: Use Task.Run with lambda to return values asynchronously [OK]

Common Mistakes:

• Trying to pass value directly to Task constructor
• Using non-existent Task.Run overloads
• Confusing Task and Task<T> creation

3. What will be the output of this C# code?

async Task<int> GetNumberAsync() { return 10; }

var task = GetNumberAsync();
Console.WriteLine(task.Result);

medium

A. Task<int>

B. 10

C. Compilation error

D. Deadlock or runtime error

Solution

1. Step 1: Understand async method returning Task<int>

   The method returns a Task that completes with value 10.

2. Step 2: Accessing task.Result

   Accessing Result blocks until the task finishes and returns 10.

3. Final Answer:

   10 -> Option B

4. Quick Check:

   Task.Result blocks and returns value = 10 [OK]

Hint: Task.Result blocks and returns the result value [OK]

Common Mistakes:

• Expecting Task<int> printed instead of value
• Thinking async method returns int directly
• Assuming runtime error without synchronization context

4. Identify the error in this code snippet:

Task<int> task = Task.Run(() => 42);
int result = await task;

medium

A. Task<int> must be declared as void

B. Task.Run cannot return int

C. Cannot use await outside an async method

D. Missing parentheses in Task.Run

Solution

1. Step 1: Check usage of await keyword

   await can only be used inside methods marked with async.

2. Step 2: Analyze code context

   The snippet does not show an async method, so using await here causes a compile error.

3. Final Answer:

   Cannot use await outside an async method -> Option C

4. Quick Check:

   Await requires async method = Cannot use await outside an async method [OK]

Hint: Always mark method async to use await inside it [OK]

Common Mistakes:

• Assuming Task.Run cannot return int
• Thinking Task<int> can be void
• Ignoring async keyword requirement for await

5. You want to run two tasks in parallel: one returns an int, the other returns a string. How do you wait for both and get their results efficiently?

hard

A. Use Task.WaitAll(task1, task2) and cast results to correct types.

B. Call task1.Wait() and task2.Wait() sequentially, then get results.

C. Use await task1 then await task2 one after another.

D. Use await Task.WhenAll(task1, task2) then access task1.Result and task2.Result.

Solution

1. Step 1: Understand parallel task waiting

   Task.WhenAll waits for all tasks to complete concurrently.

2. Step 2: Access results after waiting

   After await Task.WhenAll(...), you can safely access each task's Result without blocking.

3. Final Answer:

   Use await Task.WhenAll(task1, task2) then access task1.Result and task2.Result. -> Option D

4. Quick Check:

   Parallel wait with Task.WhenAll = Use await Task.WhenAll(task1, task2) then access task1.Result and task2.Result. [OK]

Hint: Use Task.WhenAll to await multiple tasks efficiently [OK]

Common Mistakes:

• Waiting tasks sequentially losing parallelism
• Using blocking Wait() causing deadlocks
• Casting results instead of accessing Task<T>.Result