Added solution using timer.AfterFunc and a duration flag. (#33)

Author: kalexmills

students/kalexmills/main.go

@@ -0,0 +1,112 @@
+package main
+
+import (
+"encoding/csv"
+"flag"
+"fmt"
+"log"
+"os"
+"time"
+)
+
+var (
+	filename  string
+	timelimit time.Duration
+)
+
+func init() {
+	flag.StringVar(&filename, "in", "problems.csv", "filename where problems are read from")
+	flag.DurationVar(&timelimit, "time", 30*time.Second, "time to allot for quiz")
+}
+
+
+// problem represents a prompt and the correct response
+type problem struct {
+	prompt   string
+	response string
+}
+
+// printResults prints a prompt to the user explaining the results achieved.
+func printResults(nWrong, nTotal int) {
+	nRight := nTotal - nWrong
+	fmt.Printf("You answered %d out of %d questions correctly.\n", nRight, nTotal)
+}
+
+// readFile reads from the file, sending back a slice of problems.
+func readFile() []problem {
+	file, err := os.Open(filename)
+	if err != nil {
+		log.Fatal("Error opening file: %s", err.Error())
+	}
+
+	r := csv.NewReader(file)
+	records, err := r.ReadAll()
+
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Construct a slice of problems for later consumption
+	result := make([]problem, len(records))
+	var i int
+	for idx, rec := range records {
+		if len(rec) < 2 {
+			fmt.Println("Ignoring faulty or missing record from line %d", idx)
+			continue
+		}
+		result[i] = problem{rec[0], rec[1]}
+		i++
+	}
+
+	return result
+}
+
+func main() {
+	flag.Parse()
+
+	problems := readFile()
+
+	var nWrong, nDone int
+	// timeout is used to signal that the timer has elapsed
+	timeout := make(chan bool, 2)
+	timer := time.AfterFunc(timelimit, func() {
+		timeout <- true // signal that a timeout occurred
+	})
+
+	startTime := time.Now()
+	// Ask each question and get a response
+	for _, prob := range problems {
+		fmt.Printf("%s\n > ", prob.prompt)
+
+		// A separate goroutine must be used to accept input from each question. At first I tried to just read from
+		// Stdin on the main thread. That was a mistake. If you want to be able to interrupt the prompt when the time
+		// expires, you need to have your main thread waiting on a response from either the timer or the answer thread.
+		//
+		// Lesson is to treat user input as an asynchronous message!
+		answerCh := make(chan string)
+		go func() {
+			var answer string
+			fmt.Scanf("%s\n", &answer)
+			answerCh <- answer
+		}()
+
+		select {
+		case <-timeout:
+			fmt.Println("\nTimes up!")
+			nWrong += len(problems) - nDone // All remaining problems are marked wrong
+			printResults(nWrong, len(problems))
+			os.Exit(0)
+		case response := <-answerCh:
+			nDone++
+			if prob.response != response {
+				nWrong++
+			}
+		}
+	}
+
+	if timer.Stop() {
+		fmt.Printf("You completed the quiz with %s remaining\n", (timelimit - time.Since(startTime)).String())
+
+		printResults(nWrong, len(problems))
+	}
+}

students/kalexmills/problems.csv

@@ -0,0 +1,13 @@
+5+5,10
+7+3,10
+1+1,2
+8+3,11
+1+2,3
+8+6,14
+3+1,4
+1+4,5
+5+1,6
+2+3,5
+3+3,6
+2+4,6
+5+2,7