added argv support to the sqrt program

exercises/00-sqrt/go.go

@@ -3,8 +3,11 @@ package main
 import (
 	"fmt"
 	"math"
+	"os"
+	"strconv"
 )
 
+const usage = "usage: sqrt <number>"
 const min_threshold = 1e-200
 
 type ErrNegativeSqrt float64
@@ -32,16 +35,24 @@ func Sqrt(x float64, threshold float64) (z float64, iterations int, err error) {
 }
 
 func main() {
+	if len(os.Args) != 2 {
+		fmt.Fprintf(os.Stderr, "%v\n", usage)
+		os.Exit(1)
+	}
+	i, err := strconv.ParseFloat(os.Args[1], 32)
+	if err != nil {
+		panic(err)
+	}
 	threshold := 1.0
-	right_answer := math.Sqrt(2)
+	right_answer := math.Sqrt(i)
 	for threshold > min_threshold {
-		answer, iterations, err := Sqrt(2, threshold)
+		answer, iterations, err := Sqrt(i, threshold)
 		if err != nil {
 			panic(err)
 		}
-		fmt.Printf("%0.4g %0.4g %0.20f %0.20f %0.2d\n",
-			threshold, right_answer-answer, right_answer, answer,
-			iterations)
+		fmt.Printf("%0.4g %0.2d %0.20f %0.20f %0.4g\n",
+            threshold, iterations, right_answer, answer, 
+            right_answer-answer)
 		threshold = threshold / 10.0
 	}
 }