grade_report.kt in Kotlin

Report cards from a data class roster, a when ladder, and format strings.

// Average each student's scores and print a letter-grade report card.

data class Student(val name: String, val scores: List<Int>)

val ROSTER = listOf(
    Student("Ada", listOf(92, 88, 97)),
    Student("Grace", listOf(84, 91, 78)),
    Student("Alan", listOf(70, 66, 74)),
    Student("Edsger", listOf(58, 67, 61)),
)

fun letter(avg: Double): Char = when {
    avg >= 90 -> 'A'
    avg >= 80 -> 'B'
    avg >= 70 -> 'C'
    avg >= 60 -> 'D'
    else -> 'F'
}

fun main() {
    println("student  avg grade")
    for (s in ROSTER.sortedBy { it.name }) {
        val avg = s.scores.average()
        println("%-8s %4.1f  %c".format(s.name, avg, letter(avg)))
    }
    val classAvg = ROSTER.flatMap { it.scores }.average()
    println("Class average: %.1f".format(classAvg))
}

How it works

1. Student is a data class; ROSTER holds four of them.
2. letter maps an average to a grade with a subjectless when.
3. flatMap pools every score for the class average at the end.

Keywords and builtins used here

• Char
• Double
• Int
• String
• Student
• class
• data
• else
• for
• fun
• in
• it
• letter
• main
• val
• when

The run, in numbers

Lines

28

Characters to type

706

Tokens

232

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 214 seconds.

Type this snippet

Step 2 of 3 in Encore, step 26 of 27 in Language basics.

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