error-exercise.go

package main

import (
"fmt"
"math"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
return fmt.Sprintf("cannot Sqrt negative number: %.0f", e)
}

func Sqrt(x float64) (float64, error) {
if x < 0 {
return 0, ErrNegativeSqrt(x)
}

t, z := 0., 1.
   for {
    z, t = z - (z*z-x)/(2*z), z
    if math.Abs(t-z) < 1e-8 {
        break
       }
    }
return z, nil
}

func main() {
   fmt.Println(Sqrt(2))
   fmt.Println(Sqrt(-2))
}