Exercise: Loops and Functions, https://go-tour-jp.appspot.com/flowcontrol/8

main.go

package main

import (
	"fmt"
	"math"
)

// Newton-Raphson method
func Sqrt(x float64) (result float64, count int) {
	z := 1.0
	i := 0
	var prev float64 = 1.0
	init := false
	for {
		i++
	    prev = z
        z -= (z * z - x ) / (2 * z)
		//fmt.Println(z, prev, prev < z + 0.00000000001)
		if z == prev || (init && prev < z + 0.00000000001) {
		    break
		}
		init = true
	} 
    return z, i
}

func main() {
    input := float64(67000000000)
    result, count := Sqrt(input)
	fmt.Println("try", result, ", count", count)
	fmt.Println("math", math.Sqrt(input))
}