Returning values from async methods in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an async method that returns an integer.

C Sharp (C#)

public async Task<[1]> GetNumberAsync() {
    return 42;
}

Drag options to blanks, or click blank then click option'

ATask

Bvoid

Cstring

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using void as return type for async methods that return a value.

Using Task without specifying the type parameter.

The method returns a Task wrapping an integer, so the return type is Task<int>.

2fill in blank

medium

Complete the code to await an async method and get its result.

C Sharp (C#)

int result = await GetNumberAsync();
Console.WriteLine([1]);

Drag options to blanks, or click blank then click option'

Aawait

BGetNumberAsync()

Cresult

DTask<int>

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to print the method call instead of the awaited result.

Using await inside Console.WriteLine without storing the result.

You should print the variable result which holds the awaited value.

3fill in blank

hard

Fix the error in the async method to correctly return a string value.

C Sharp (C#)

public async Task<string> GetMessageAsync() {
    [1] "Hello";
}

Drag options to blanks, or click blank then click option'

Areturn

Byield

Cawait

Dthrow

Attempts:

3 left

💡 Hint

Common Mistakes

Using await without returning a value.

Using yield in an async method.

Async methods returning a value must use return to send back the result.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that filters async results.

C Sharp (C#)

var results = new Dictionary<string, int> {
    {"score", [1],
    {"count", [2]
};

Drag options to blanks, or click blank then click option'

Aawait GetScoreAsync()

Bawait GetCountAsync()

CGetScoreAsync()

DGetCountAsync()

Attempts:

3 left

💡 Hint

Common Mistakes

Using async method calls without await, resulting in Task objects instead of values.

Mixing awaited and non-awaited calls.

To get the actual values from async methods, you must await them.

5fill in blank

hard

Fill all three blanks to create an async method that returns a dictionary with awaited values.

C Sharp (C#)

public async Task<Dictionary<string, int>> GetDataAsync() {
    return new Dictionary<string, int> {
        {"a", [1],
        {"b", [2],
        {"c", [3]
    };
}

Drag options to blanks, or click blank then click option'

Aawait GetAAsync()

Bawait GetBAsync()

Cawait GetCAsync()

DGetAAsync()

Attempts:

3 left

💡 Hint

Common Mistakes

Returning Tasks instead of awaited results.

Forgetting to await one or more async calls.

Each async method call must be awaited to get the integer values before returning the dictionary.

Practice

1. What type should an async method return if it needs to return a value of type int?

easy

A. void

B. Task

C. int

D. Task<int>

Solution

1. Step 1: Understand async method return types

   Async methods that return a value must return Task<T> where T is the value type.

2. Step 2: Match the return type to the value type

   Since the method returns an int, the return type should be Task<int>.

3. Final Answer:

   Task<int> -> Option D

4. Quick Check:

   Async method returning int uses Task<int> [OK]

Hint: Async methods returning values use Task<T> [OK]

Common Mistakes:

• Using void for async methods that return values
• Returning int directly from async method
• Using Task without generic type for returning values

2. Which of the following is the correct syntax to declare an async method that returns a string value?

easy

A. async Task<string> GetNameAsync()

B. string async Task GetNameAsync()"

C. Task async string GetNameAsync()

D. async string GetNameAsync()

Solution

1. Step 1: Identify correct async method syntax

   An async method returning a value must have the signature: async Task<T> MethodName().

2. Step 2: Check each option

   async Task<string> GetNameAsync() matches the correct syntax: async Task<string> GetNameAsync(). Others have wrong order or missing Task<T>.

3. Final Answer:

   async Task<string> GetNameAsync() -> Option A

4. Quick Check:

   Async method returning string uses async Task<string> [OK]

Hint: Async method syntax: async Task<T> MethodName() [OK]

Common Mistakes:

• Placing async after return type
• Using string directly without Task<>
• Mixing order of async and Task keywords

3. What will be the output of the following code?

async Task<int> GetNumberAsync() { return 5; }

async Task Main()
{
    int result = await GetNumberAsync();
    Console.WriteLine(result);
}

medium

A. Task<int>

B. 5

C. Compilation error

D. 0

Solution

1. Step 1: Understand async method return and await

   The method GetNumberAsync returns a Task<int> with value 5. Await unwraps the value.

2. Step 2: Check what is printed

   The awaited result is 5, so Console.WriteLine(result) prints 5.

3. Final Answer:

   5 -> Option B

4. Quick Check:

   Await unwraps Task<int> to int value 5 [OK]

Hint: Await unwraps Task<T> to get the value [OK]

Common Mistakes:

• Printing Task<int> instead of awaited int
• Expecting compilation error due to async
• Assuming default int value 0 is printed

4. Identify the error in this async method:

async Task<int> CalculateAsync()
{
    int value = 10;
    return Task.FromResult(value);
}

medium

A. No error, code is correct

B. Method should return int, not Task<int>

C. Missing await keyword before Task.FromResult

D. Returning Task.FromResult inside async method causes nested Task

Solution

1. Step 1: Analyze return statement in async method

   Async methods can return Task<T> directly, such as Task.FromResult(value), which is a common and valid pattern for completed tasks.

2. Step 2: Verify the code runs correctly

   The async state machine properly handles the returned Task<int>, producing a single Task<int> with value 10 for the caller. No nesting or errors occur.

3. Final Answer:

   No error, code is correct -> Option A

4. Quick Check:

   Task.FromResult is valid in async Task<int> methods [OK]

Hint: Task.FromResult(value) is valid in async Task<T> methods [OK]

Common Mistakes:

• Misunderstanding that Task.FromResult causes nested Tasks
• Thinking async methods must return T directly, not Task<T>
• Believing await is required before Task.FromResult

5. You want to write an async method that fetches user data and returns the user's name as a string. The fetching is simulated by a delay. Which of the following implementations correctly returns the name without blocking the caller?

hard

A. async string GetUserNameAsync() { await Task.Delay(1000); return \"Alice\"; }

B. Task<string> GetUserNameAsync() { return \"Alice\"; }

C. async Task<string> GetUserNameAsync() { await Task.Delay(1000); return \"Alice\"; }

D. async Task GetUserNameAsync() { await Task.Delay(1000); return \"Alice\"; }"

Solution

1. Step 1: Check method signature and return type

   The method must be async and return Task<string> to return a string asynchronously.

2. Step 2: Verify method body and return statement

   async Task<string> GetUserNameAsync() { await Task.Delay(1000); return \"Alice\"; } uses await Task.Delay(1000) to simulate delay and returns the string correctly. Others have wrong return types or missing async.

3. Final Answer:

   async Task<string> GetUserNameAsync() { await Task.Delay(1000); return "Alice"; } -> Option C

4. Quick Check:

   Async method returning string uses async Task<string> with await [OK]

Hint: Async method returning value uses async Task<T> with await [OK]

Common Mistakes:

• Returning string directly without Task
• Using async with wrong return type
• Missing await causing blocking