grade_report.swift in Swift

Report cards from a struct roster, range patterns, and format.

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

import Foundation

struct Student {
    let name: String
    let scores: [Int]

    var average: Double {
        Double(scores.reduce(0, +)) / Double(scores.count)
    }
}

let roster = [
    Student(name: "Ada", scores: [92, 88, 97]),
    Student(name: "Grace", scores: [84, 91, 78]),
    Student(name: "Alan", scores: [70, 66, 74]),
    Student(name: "Edsger", scores: [58, 67, 61]),
]

func letter(_ avg: Double) -> String {
    switch avg {
    case 90...: return "A"
    case 80...: return "B"
    case 70...: return "C"
    case 60...: return "D"
    default: return "F"
    }
}

print("student  avg grade")
for s in roster.sorted(by: { $0.name < $1.name }) {
    let name = s.name.padding(toLength: 8, withPad: " ", startingAt: 0)
    let avg = String(format: "%4.1f", s.average)
    print("\(name) \(avg)  \(letter(s.average))")
}

let allScores = roster.flatMap { $0.scores }
let classAvg = Double(allScores.reduce(0, +)) / Double(allScores.count)
print(String(format: "Class average: %.1f", classAvg))

How it works

1. Student.average is a computed property over reduce.
2. case 90...: range patterns grade the ladder.
3. flatMap pools every score for the class average.

Keywords and builtins used here

• Double
• Foundation
• Int
• String
• Student
• case
• count
• default
• for
• func
• import
• in
• let
• letter
• print
• reduce
• return
• sorted
• struct
• switch
• var

The run, in numbers

Lines

40

Characters to type

1004

Tokens

309

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 285 seconds.

Type this snippet

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

← Previous Next →