Why extension methods are needed in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an extension method for string that returns the first character.

C Sharp (C#)

public static class StringExtensions {
    public static char [1](this string str) {
        return str[0];
    }
}

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

AFirstChar

BGetFirst

CStartChar

DCharAt

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not clearly describe its purpose.

The method name 'FirstChar' clearly describes the extension method's purpose.

2fill in blank

medium

Complete the code to call the extension method on a string variable.

C Sharp (C#)

string name = "Alice";
char first = name.[1]();

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AGetFirst

BCharAt

CStartChar

DFirstChar

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the method as a static method instead of an instance method.

The extension method 'FirstChar' is called like a normal method on the string instance.

3fill in blank

hard

Fix the error in the extension method definition by completing the missing keyword.

C Sharp (C#)

public static class StringExtensions {
    public static char FirstChar([1] string str) {
        return str[0];
    }
}

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

Apublic

Bstatic

Cthis

Dreadonly

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the 'this' keyword, which causes the method not to be an extension method.

The 'this' keyword before the first parameter marks it as an extension method.

4fill in blank

hard

Complete the code to create an extension method that checks if a string contains only digits.

C Sharp (C#)

public static bool [1](this string str) {
    return str.All(c => char.IsDigit(c));
}

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

AIsDigitsOnly

B=>

C=>=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect lambda syntax or method name.

The method name 'IsDigitsOnly' describes the check, and '=>' is the lambda arrow used in the All method.

5fill in blank

hard

Fill all three blanks to create an extension method that repeats a string n times.

C Sharp (C#)

public static string [1](this string str, int [2]) {
    return string.Concat(Enumerable.[3](str, [2]));
}

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

ARepeat

Bcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names or method names.

Not using Enumerable.Repeat correctly.

The method name is 'Repeat', the parameter is 'count', and the Enumerable method is 'Repeat' to repeat the string.