Why LINQ depends on extension methods in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an extension method for IEnumerable<int>.

C Sharp (C#)

public static class Extensions {
    public static int Sum(this IEnumerable<int> [1]) {
        int total = 0;
        foreach (var num in source) {
            total += num;
        }
        return total;
    }
}

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

Asource

Bitem

Clist

Dcollection

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name that is not descriptive or not valid as an identifier.

Forgetting the this keyword before the parameter.

The parameter name for the extension method must be a valid identifier. Here, source is commonly used to represent the input collection.

2fill in blank

medium

Complete the code to call the extension method on a list.

C Sharp (C#)

var numbers = new List<int> {1, 2, 3};
int total = numbers.[1]();

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AAdd

BSort

CCount

DSum

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods that do not return a sum like Add or Sort.

Forgetting that extension methods appear as if they are instance methods.

The Sum method is an extension method that calculates the total of all elements in the list.

3fill in blank

hard

Fix the error in the extension method declaration.

C Sharp (C#)

public static int CountItems([1]) {
    int count = 0;
    foreach (var item in source) {
        count++;
    }
    return count;
}

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Athis IEnumerable<int> source

Bthis source

Csource

DIEnumerable<int> this source

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the this keyword.

Placing this after the type or parameter name incorrectly.

Extension methods must have the this keyword before the first parameter's type to indicate the method extends that type.

4fill in blank

hard

Fill both blanks to create an extension method that filters even numbers.

C Sharp (C#)

public static IEnumerable<int> [1](this IEnumerable<int> source) {
    foreach (var num in source) {
        if (num [2] 2 == 0) {
            yield return num;
        }
    }
}

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AWhereEven

BSum

C%

DAdd

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names like Sum or Add.

Using wrong operators like + instead of modulus.

The method name WhereEven describes filtering even numbers. The modulus operator % checks divisibility.

5fill in blank

hard

Fill all three blanks to create an extension method that converts strings to uppercase and filters by length.

C Sharp (C#)

public static IEnumerable<string> [1](this IEnumerable<string> source, int minLength) {
    foreach (var str in source) {
        var upper = str.[2]();
        if (upper.Length [3] minLength) {
            yield return upper;
        }
    }
}

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

AFilterAndUpper

BToUpper

C>=

DToLower

Attempts:

3 left

💡 Hint

Common Mistakes

Using ToLower instead of ToUpper.

Using wrong comparison operators like <.

The method name FilterAndUpper describes the operation. ToUpper() converts strings to uppercase. The operator >= filters strings with length greater or equal to minLength.