Control Flow for Kotlin lang (#26793)

* Create control_flow.md

* Rename control_flow.md to controlflow.md

* Added control flow

* Added classes

* fix: corrected indentation

* fix: corrected indentation

guide/english/kotlin/classes/index.md

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+---
+title: Classes
+---
+
+# Classes
+
+### Basic Usage
+
+#### Declaration
+
+`class` keyword is used to define the class  
+It is consisted of: class name, class header (type parameters, constructor) and class body (curly braces)  
+```kotlin
+class Person { ... }
+```
+
+#### Constructor
+
+There are multiple ways to define class constructor.  
+Primary constructor is part of the class header (name field with data type):
+```kotlin
+class Person(name: String) { ... }
+```
+
+Secondary constructor: using `constructor` keyword inside class body  
+```kotlin
+class Person {
+  constructor(parent: Person) {
+    parent.children.add(this)
+  }
+}
+```
+
+#### Usage
+
+Class instance can be created as regular function   
+There is no need for `new` keyword
+```kotlin
+val john = Person("John Wayne")
+```
+
+#### Resources
+* [Basic Syntax Reference](https://kotlinlang.org/docs/reference/basic-syntax.html)
+* [Kotlin Classes Reference](https://kotlinlang.org/docs/reference/classes.html)

guide/english/kotlin/control-flow/index.md

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+---
+title: Control Flow
+---
+
+# Control Flow
+
+### Basic Usage
+
+#### If Expression
+
+`if` can be used in same way as in other programming languages
+```kotlin
+var min: Int
+if (a < b) {
+  min = a
+} else {
+  min = b
+}
+```
+
+`else` can also be omitted if not needed
+```kotlin
+if (a < b) {
+  print("a is smaller")
+}
+```
+
+#### When Expression
+
+`when` keyword is replacing usual `switch-case` expression  
+The else branch is evaluated if none of the other branch conditions are satisfied  
+It has powerfull matching branches which support complex evaluations of input argument  
+```kotlin
+when (obj) {
+  1          -> "One"
+  1, 2       -> "One or Two"
+  "Hello"    -> "Greeting"
+  is Long    -> "Long"
+  !is String -> "Not a string"
+  else       -> "Unknown"
+}
+```
+
+Range evaluation
+```kotlin
+when (x) {
+  in 1..100 -> print("x is in the range")
+  in validNumbers -> print("x is valid")
+  !in 10..200 -> print("x is outside the range")
+  else -> print("none of the above")
+}
+```
+
+#### For Loops
+
+`for` loop can iterate through anything that provides and interator, using `in` operator
+```kotlin
+val fruits = listOf("apple", "banana", "kiwi")
+for (fruit in fruits) {
+  println(fruit)
+}
+```
+
+Iterating through range of numbers
+```kotlin
+for (i in 1..5) {
+  println(i)
+}
+```
+
+#### While Loops
+
+`while` and `do..while` are used like in most programming languages
+```kotlin
+while (a > 0) {
+  a--
+}
+
+do {
+  val b = provideData()
+} while (b != null)
+```
+
+#### Break and continue keywords
+Used like in most other programming languages
+
+#### Resources
+* [Basic Syntax Reference](https://kotlinlang.org/docs/reference/basic-syntax.html)
+* [Kotlin Control Flow Reference](https://kotlinlang.org/docs/reference/control-flow.html)