Accept an arg for the number of fibs to generate.

exercises/03-fibonacci/fibonacci.go

@@ -1,6 +1,13 @@
 package main
 
-import "fmt"
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+var usage string = "usage: " + os.Args[0] + " <number of fibs>"
 
 // fibonacci is a function that returns
 // a function that returns an int.
@@ -22,8 +29,18 @@ func fibonacci() func() int {
 }
 
 func main() {
+	flag.Parse()
+	if len(flag.Args()) != 1 {
+		fmt.Fprintln(os.Stderr, usage)
+		os.Exit(1)
+	}
+	count, err := strconv.Atoi(flag.Arg(0))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s\n", err.Error())
+		os.Exit(1)
+	}
 	f := fibonacci()
-	for i := 0; i < 20; i++ {
+	for i := 0; i < count; i++ {
 		fmt.Println(f())
 	}
 }