C# 1001 notes

📝 What is Boxing and Unboxing?

Boxing and Unboxing both are used for type conversion but have some difference:

🔸 Boxing is the process of converting a value type data type to the object or to any interface data type which is implemented by this value type. When the CLR boxes a value means when CLR is converting a value type to Object Type, it wraps the value inside a System.Object and stores it on the heap area in application domain.

🔸 Unboxing is also a process which is used to extract the value type from the object or any implemented interface type. Boxing may be done implicitly, but unboxing have to be explicit by code.

The concept of boxing and unboxing underlines the C# unified view of the type system in which a value of any type can be treated as an object.

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✨ Here is a solution for the #challenge above

#challenge

💻 Oddish vs. Evenish | #easy

Create a function that determines whether a number is Oddish or Evenish. A number is Oddish if the sum of all of its digits is odd, and a number is Evenish if the sum of all of its digits is even. If a number is Oddish, return "Oddish". Otherwise, return "Evenish".

For example, OddishOrEvenish(121) should return "Evenish", since 1 + 2 + 1 = 4. OddishOrEvenish(41) should return "Oddish", since 4 + 1 = 5.

Examples:

OddishOrEvenish(43) ➞ "Oddish"
// 4 + 3 = 7
// 7 % 2 = 1

OddishOrEvenish(373) ➞ "Oddish"
// 3 + 7 + 3 = 13
// 13 % 2 = 1

OddishOrEvenish(4433) ➞ "Evenish"
// 4 + 4 + 3 + 3 = 14
// 14 % 2 = 0

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

#interview

📝 What is Weak Reference in C#?

The garbage collector cannot collect an object in use by an application while the application's code can reach that object. The application is said to have a strong reference to the object.

A weak reference permits the garbage collector to collect the object while still allowing the application to access the object. A weak reference is valid only during the indeterminate amount of time until the object is collected when no strong references exist.

Weak references are useful for objects that use a lot of memory, but can be recreated easily if they are reclaimed by garbage collection.

Suppose a tree view in a Windows Forms application displays a complex hierarchical choice of options to the user. If the underlying data is large, keeping the tree in memory is inefficient when the user is involved with something else in the application.

When the user switches away to another part of the application, you can use the WeakReference class to create a weak reference to the tree and destroy all strong references. When the user switches back to the tree, the application attempts to obtain a strong reference to the tree and, if successful, avoids reconstructing the tree.

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📝 What are the different types of classes in C#?

The different types of class in C# are:

🔸 Partial class – Allows its members to be divided or shared with multiple .cs files. It is denoted by the keyword Partial.

🔸 Sealed class – It is a class which cannot be inherited. To access the members of a sealed class, we need to create the object of the class. It is denoted by the keyword Sealed.

🔸 Abstract class – It is a class whose object cannot be instantiated. The class can only be inherited. It should contain at least one method. It is denoted by the keyword abstract.

🔸 Static class – It is a class which does not allow inheritance. The members of the class are also static. It is denoted by the keyword static. This keyword tells the compiler to check for any accidental instances of the static class.

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✨ Here is a solution for the #challenge above

#challenge

💻 Pentagonal Number | #easy

Write a function that takes a positive integer num and calculates how many dots exist in a pentagonal shape around the center dot on the Nth iteration.

In the image below you can see the first iteration is only a single dot. On the second, there are 6 dots. On the third, there are 16 dots, and on the fourth there are 31 dots.

Return the number of dots that exist in the whole pentagon on the Nth iteration.

Examples:

pentagonal(1) ➞ 1
pentagonal(2) ➞ 6
pentagonal(3) ➞ 16
pentagonal(8) ➞ 141

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

#interview

📝 What are the benefits of a Deferred Execution in LINQ?

In LINQ, queries have two different behaviors of execution: immediate and deferred.

Deferred execution means that the evaluation of an expression is delayed until its realized value is actually required. It greatly improves performance by avoiding unnecessary execution.
Consider:

 results = collection
  .Select(item => item.Foo)
  .Where(foo => foo < 3)
  .ToList();

With deferred execution, the above iterates your collection one time, and each time an item is requested during the iteration, performs the map operation, filters, then uses the results to build the list.

If you were to make LINQ fully execute each time, each operation (Select / Where) would have to iterate through the entire sequence. This would make chained operations very inefficient.

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📝 How we can pass parameters to a method?

There are three ways that parameters can be passed to a method:

🔸 Value parameters − This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument.

🔸 Reference parameters − This method copies the reference to the memory location of an argument into the formal parameter. This means that changes made to the parameter affect the argument.

🔸 Output parameters − This method helps in returning more than one value.

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✨ Here is a solution for the #challenge above

#challenge

💻 Letter Distance | #easy

Given two words, the letter distance is calculated by taking the absolute value of the difference in character codes and summing up the difference.

If one word is longer than another, add the difference in lengths towards the score.

To illustrate:

 "fly") = dist("h", "f") + dist("o", "l") + dist("u", "y") + dist(house.Length, fly.Length)

= |104 - 102| + |111 - 108| + |117 - 121| + |5 - 3|
= 2 + 3 + 4 + 2
= 11

Examples:

LetterDistance("sharp", "sharq") ➞ 1
LetterDistance("abcde", "Abcde") ➞ 32
LetterDistance("abcde", "bcdef") ➞ 5

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

#interview

📝 How can we check equality in .NET?

🔸 The ReferenceEquals() method - checks if two reference type variables(classes, not structs) are referred to the same memory address.

🔸 The virtual Equals() method. (System.Object) - checks if two objects are equivalent.

🔸 The static Equals() method - is used to handle problems when there is a null value in the check.

🔸 The Equals method from IEquatable interface.

🔸 The comparison operator == - usually means the same as ReferenceEquals, it checks if two variables point to the same memory address. The gotcha is that this operator can be override to perform other types of checks. In strings, for instance, it checks if two different instances are equivalent.

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