Add errors

sqrterr.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"fmt"
+)
+type ErrNegativeSqrt float64
+
+func (e ErrNegativeSqrt) Error() string {
+	return fmt.Sprintf("cannot Sqrt negative number: %f", float64(e))
+}
+
+func Sqrt(x float64) (float64, error) {
+	if x < 0 {
+		return 0, ErrNegativeSqrt(x)
+	}
+	z := 1.0
+	for count := 0; count < 10; count++ {
+		z -= (z*z - x) / (2*z)
+	}
+	return z, nil
+}
+
+func main() {
+	fmt.Println(Sqrt(2))
+	fmt.Println(Sqrt(-2))
+}