Jetpack Compose

    // VARIABLES
    val appName = "ComposeNotes" - inmutable
    var notificationCount = 0   - mutable

    val username:String ="Alex"
    val age:Int = 30
    val rating:Double = 4.5
    val isActive:Boolean = true

    Null: by default variables cannot hold null.
    To allow null, we can use the ? operator var name:String? = null
    Safe call operator: name?.length - returns null if name is null
    Elvis operator: 
        name?.length ?: 0 - returns 0 if name is null 
        val imageUrl = profileImageUrl ?: "default_image.png" - returns default image if profileImageUrl is null
    let: name?.let { println("Name is $it") } - executes the block only if name is not null


    

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