C# 1001 notes

📝 What is namespace in C#?

A namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace does not conflict with the same class names declared in another.

🔸 NET uses namespaces to organize its many classes.

🔸 Declaring your own namespaces can help you control the scope of class and method names in larger programming projects.

 SampleNamespace
{
    class SampleClass
    {
        public void SampleMethod()
        {
            System.Console.WriteLine(
              "SampleMethod inside SampleNamespace");
        }
    }
}

#post

✨ Here is a solution for the #challenge above

#challenge

💻 Compounding Letters | #easy

Create a function that takes a string and returns a new string with each new character accumulating by +1. Separate each set with a dash.

Capitalize the first letter of each set.

Examples:

Accum("abcd") ➞ "A-Bb-Ccc-Dddd"
Accum("RqaEzty") ➞ "R-Qq-Aaa-Eeee-Zzzzz-Tttttt-Yyyyyyy"
Accum("cwAt") ➞ "C-Ww-Aaa-Tttt"

🏆 Leave your solutions in the comments. The solution will be posted below in a couple of hours 👇

#interview

📝 How to implement the Where method in C#?

The yield keyword actually does quite a lot here. It creates a state machine "under the covers" that remembers where you were on each additional cycle of the function and picks up from there.

The function returns an object that implements the IEnumerable<T> interface. If a calling function starts foreaching over this object, the function is called again until it "yields" result based on some predicate.

This is syntactic sugar introduced in C# 2.0. In earlier versions you had to create your own IEnumerable and IEnumerator objects to do stuff like this.

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📝 What is an Abstract Class?

The abstract modifier indicates that the thing being modified has a missing or incomplete implementation. The abstract modifier can be used with classes, methods, properties, indexers, and events.

An Abstract class is a class which is denoted by abstract keyword and can be used only as a Base class.

Abstract classes have the following features:

🔸 An abstract class cannot be instantiated.

🔸 An abstract class may contain abstract methods and accessors.

🔸 It is not possible to modify an abstract class with the sealed modifier because the two modifiers have opposite meanings. The sealed modifier prevents a class from being inherited and the abstract modifier requires a class to be inherited.

🔸 A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors.

#post

✨ Here is a solution for the #challenge above

💬 At first blush, it seems tricky but, in my opinion, this solution is really graceful

#challenge

💻 Largest Gap | #easy

Given an array of integers, return the largest gap between elements of the sorted version of that array.

Here's an illustrative example. Consider the array:

9, 4, 26, 26, 0, 0, 5, 20, 6, 25, 5

... which, after sorting, becomes the array:

0, 0, 4, 5, 5, 6, 9, 20, 25, 26, 26

... so that we now see that the largest gap in the array is the gap of 11 between 9 and 20.

Examples:

LargestGap(new int[] { 9, 4, 26, 26, 0, 0, 5, 20, 6, 25, 5 }) ➞ 11
// After sorting get { 0, 0, 4, 5, 5, 6, 9, 20, 25, 26, 26 }
// Largest gap of 11 between 9 and 20

LargestGap(new int[] { 14, 13, 7, 1, 4, 12, 3, 7, 7, 12, 11, 5, 7 }) ➞ 4
// After sorting get { 1, 3, 4, 5, 7, 7, 7, 7, 11, 12, 12, 13, 14 }
// Largest gap of 4 between 7 and 11

🏆 Leave your solutions in the comments. The solution will be posted below in a couple of hours 👇

#interview

All of these interfaces inherit from IEnumerable. That interface basically lets you use the class in a foreach statement (in C#).

🔸 ICollection is the most basic of the interfaces you listed. It's an enumerable interface that supports a Count and that's about it.

🔸 IList is everything that ICollection is, but it also supports adding and removing items, retrieving items by index, etc. It's the most commonly-used interface for "lists of objects".

🔸 IQueryable is an enumerable interface that supports LINQ. You can always create an IQueryable from an IList and use LINQ to Objects, but you also find IQueryable used for deferred execution of SQL statements in LINQ to SQL and LINQ to Entities.

🔸 IDictionary is a different animal in the sense that it is a mapping of unique keys to values. It is also enumerable in that you can enumerate the key/value pairs, but otherwise it serves a different purpose than the others you listed.

#post

📝 What is the difference between a Struct and a Class in C#?

Class and struct both are the user defined data type but have some major difference:

Struct

🔸 The struct is value type in C# and it inherits from System.Value Type.

🔸 Struct is usually used for smaller amounts of data.

🔸 Struct can't be inherited to other type.

🔸 A structure can't be abstract.

Class

🔸 The class is reference type in C# and it inherits from the System.Object Type.

🔸 Classes are usually used for large amounts of data.

🔸 Classes can be inherited to other class.

🔸 A class can be abstract type.

🔸 We can create a default constructor.

#post

✨ Here is a solution for the #challenge above

#challenge

💻 Is the Input Factorial of an Integer? | #easy

Create a function that checks if a given integer is exactly the factorial of an integer or not. true if it is, false otherwise.

Examples:

isFactorial(2) ➞ true
// 2 = 2 * 1 = 2!

isFactorial(27) ➞ false

isFactorial(24) ➞ true
// 24 = 4 * 3 * 2 * 1 = 4!

🏆 Leave your solutions in the comments. The solution will be posted below in a couple of hours 👇

#interview

📝 You have defined a destructor but it never executed. Why?

The runtime environment automatically invokes the destructor of a class to release the resources that are occupied by variables and methods of an object.

However, in C#, programmers cannot control the timing for invoking destructors, as Garbage Collector is only responsible for releasing the resources used by an object.

Garbage Collector automatically gets information about unreferenced objects from .NET's runtime environment and then invokes the Finalize() method.

Although, it is not preferable to force Garbage Collector to perform garbage collection and retrieve all inaccessible memory (programmers can use the Collect() method of the Garbage Collector class to forcefully execute Garbage Collector).

Take notice that the destructor doesn't (and can't) have a public modifier in-front of it, it's sort of an hint that you can't explicitly call the destructor of an object.

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📝 What are Property Accessors?

The get and set portions or blocks of a property are called accessors.

These are useful to restrict the accessibility of a property.

🔸 The set accessor specifies that we can assign a value to a private field in a property and without the set accessor property it is like a read-only field.

🔸 By the get accessor we can access the value of the private field. A Get accessor specifies that we can access the value of a field publicly.

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