Unnecessary toUpperCase() and toLowerCase() functions with Kotlin

main.kt

fun main() {
    print("Enter your name: ")

    val input = readLine()
    if (input != null) {
        println("Name: $input")

        // print the result using our 'String.toUpperCase()' func
        println("toUpperCase  : ${input.toUpperCase()}")

        // print the result using our 'String.toLowerCase()' func
        println("toLowerCase  : ${input.toLowerCase()}")
    }
}

fun String.toUpperCase(): String {
    // we will collect the output in 'output' variable
    // because we need to modify this variable on runtime, we define it as 'var'
    var output = ""

    // first, we'll iterate the String, bcs basically a String is an array of char
    for (i in this) {

        // if the char is a lowercase letter
        if (i in 'a'..'z') {

              // then we will run our formula
              output += (i.code - 32).toChar()
        } else { 

              // else, we assume this char was already in uppercase letter
              output += i
        }
    }
    return output
}

fun String.toLowerCase(): String {
    var output = ""
    for (i in this) {

        // now we check whether the char is an uppercase letter
        if (i in 'A'..'Z') {

            // then we will run our formula
            output += (i.code + 32).toChar()
        } else {

            // else, we assume this char was already in lowercase letter
            output += i
        }
    }
    return output
}