Kotlin Cheat Sheet

1. Function

   fun main() {
   	myFunction("Abigail")
   }
      
   fun myFunction(name: String) {
       println("Hello, $name!")
   }
   

2. Declaration

   // val: read-only
   val firstName: String = "Abigail" // type declaration can be omitted because Kotlin has type inference
   // var: read and write
   var myBool: Boolean = false
   var myDouble: Double = 2.5
   

3. String Operations

   val myString = "Kotlin"
   println(myString.length)
   println(myString[0]) // index, starting from 0
   println(myString.substring(2, 4)) // slice, equals `myString[2:4]` in Python
   println(myString.isEmpty())
   println("The string is $myString") // string interpolation
   

4. print

   println("Hello World!") // with '\n' in the end
   print("Hello World!") // No '\n' in the end
   

5. Collections

    val names = listOf("friend1", "friend2", "friend3") // cannot add or remove elements
       
    val mutableNames = mutableListOf<String>("mfriend1", "mfriend2", "mfriend3")
    mutableNames.add("mfriend4") // OK, names is a mutable list of type String
    mutableNames.add(80) // Error, type mismatch
   

6. Condition

    val examScore = 88
    if (examScore > 70) {
        println("You passed!")
    } else {
        println("You failed :(")
    }
   

7. For Loop

   val mutableNames = mutableListOf<String>("mfriend1", "mfriend2", "mfriend3")
   for (name in mutableNames) {
       println(name)
   }
      
   for (i in 1..5) {
       println(i)
   }
   

8. Nullability

   val instagramBio: String? = null
   if (instagramBio != null) {
       println(instagramBio.toUpperCase())
   }
   println(instagramBio?.toUpperCase())
   

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