KOTLIN-BASICS

Variable decleartion ------------------------->>

 we have main function first of all 

fun main (){
    print("hello world")
}

here 'fun' defining a function whose name is main
print("text_here") use to print text in kotline

we can define variable by keyword var which are changable

fun main(){
    var myName = "DDaku"
    myName  = "Suppandi"
    print("Hello "+ myName)
}

output will be : Hello Suppandi

Now variable declare by keyword val are cannot be changed for example 

fun main(){
    val myName = "DDaku"
    myName = "Suppandi"        ::::: will throw an error : val can not be reassigned
}

comment :: // this is a comment nothing to do with logic and code but covers only single line 

                :: /* this is a multiline comment also have nothing to do with
                    but can spread to multiple lines */

 

Data Types ------------------------------>> 

variable types  : number type

var myName = "Suppandi" // type string 

var myAge = 31 // type int 32 bit 
var myByte : Byte = 13 // 8but
var myShort ; Short= 125// 16bit
var myInt : Int  = 19 // 32 bit
var myLong : Long= 100000000000 // 64 bit 

val myFloat : Float = 13.37 //default is double  by giving Float we assign it a float
val myDouble : Double = 3.1415155556 

Variable type boolean : 

var isSunny : Boolean = true
isSunny = false 

//character type 

val letterChar = 'A'
val digitChar = '1'

// string type 

val myStr = "Hello World"
val fristCharInStr = myStr[0]
val lastCharInStr= myStr[myStr.length - 1]

print("first Character of myStr string is " + firstCharInStr)
print("Last Character of myStr string is " + lastCharInStr)

String Manipulation ------------------------------------->>

print("first Character of myStr string is $firstCharInStr")
print("Last Character of myStr string is $lastCharInStr")
print("\n Length of myStr is ${myStr.length}")

Arithmatic Operators ----------------------------------->>

var resutl = 5+3 ;
result *=2
print(result)

Comparison operator --------------------------------------->>

val isEqual = 5==4
println("isEqual is  $isEqual ")
var myNum =5
myNum +=3
myNum *=4
println("myNum is $myNum")

increment and decrement operator
println("myNum is ${myNum++}")
println("myNum +2 is ${++myNum}")

If else conditions _--------------------------------------------->>

val age = 17
if(age>=21){
    println(" now you may drink in the US")
}
else if(age >=18){
    println("you may vote now ")
}
else if(age >=16) {
    println("you may drive now ")
}
else {
    print("you are too young to die")
}

if statments include a boolean variable inside it if true then execute other wise else statment gets the controle

Switch Case In Kotline ------------------------------------------>>

Switch Statments :are  much faster than if-else ledder
var season = 3
when(season){
    1 -> println("Spring")
    2 -> println("Summer")
    3 -> { println("fall")
                println("Autmn") }
    4 -> println("winter")
    else -> println("Invalid Season")
}

another way of switch case logic in kotline

var month =3

when(month){
    in 3..5 -> println("Spring")
    in 6..8 -> println("Summer")
    in 9..11-> println("Autmn")
    12,1,2 -> println("winter")
}

A very good example to go through for switch case type in kotline
var  x : Any  = 13.37f
when(x){
    is Int -> println("$x is an Int ")
    is Float -> println("$x is a float ")
    is Double -> println("$x is a double ")
    is Char -> println ("$x is a character ")
    is String -> println ("$x is a string ")
    else -> println("$x is something which is not char , int , float , double , string")

}

//---LOOPS ---------------------------------->> 

    while loop
var x =1
while ( x<=10){
    println("$x")
    x++
}

    do while loops
do{
    print("$x")
    x++
}while( x<10)

for loops

for (num  in 1..10){
    print("$num")
}

for ( i in 1 until 10) {
    print("$i ")
}

for (i in 10 down to 1 step 2){
    print("$i ")
}

The BREAK and CONTINUE statments --------------------->>

for(i in 1 untill 20){
    print("$i ")
    if( i/2 == 5 ){
       continue // telling theme to continue without listing to the code below it , ie start next iteration while break will ends this loop right here when condition is met
    }

    print("$i ")
}
println("Done with the loop")

Creating New Fuctions ----------------------->>

fun function_name ( arguments of that function ) : return_type{
    //code inside
}

fun addition ( x:Int , y:Int ) : Int {
    return (x+y)
}

fun main(){
    var a =1
    var b =2
    var add
add = addition( a, b )
    println("addition of a and b is $add ")
}

// Nullables in Kotline
null reference ,

fun main(){
    var name :String = "Suppandi"
    // name = null 
    var nullableName : String? = "Ddaku"
    nullableName = null
   
    var lengthOfName = name.length
    

if( nullableName != null){
    var len2 = nullableName.length
}else{
    null
}
    the above nullable code is same as the statment below 

var len2 = nullableName?.length

so
println(nullableName?.toLowerCase())
if empty return null
if have a string in it return it with all letters to lowercase if possible

Elvis Operator :------------------>>

val name = nullableName ?: "Guest"
means name contains value insite nullableName variable have stored in unless it is null
if it is null then the value will going to store in name variable is "Guest"

elvis operator is    ?:

nullableName!!.tolowercase() // if we are sure that nullableName is not Null

example
var name = "Suppandi"
var nullableName  : String? ="Devesh"
nullableName = null

println(" hello $name \n hello ${nullableName?:"DDaku"} ") / /will print hello Suppandi (next line) hello DDaku as nullableName is null