Go Tour: Exercise: Loops and Functions (http://tour.golang.org/flowcontrol/8)

sqrt.go

package main

import (
	"fmt"
	"math"
)

func Sqrt(x float64) float64 {
	z := 1.0
	// var a,b,c,d,e float64
	for i := 1; i <= 50; i++ {
		tmp := z
		// a = math.Pow(z,2)
		// b = math.Pow(z,2) - x
		// c = 2*z
		// d = ((math.Pow(z,2) - x) / (2*z))
		// e = z - ((math.Pow(z,2) - x) / (2*z))
		// fmt.Println(a,b,c,d,e)
		z = z - ((math.Pow(z,2) - x) / (2*z))
		fmt.Println(i,"-->",z)

		delta := math.Abs(math.Abs(z) - math.Abs(tmp))
		if delta < 0.000001 {
			break
		}
	}
	return z
}

func guessSqrt(x float64) {
	fmt.Println("Guess:", Sqrt(x), " Actual: ",  math.Sqrt(x),  "\n")
}

func main() {
	guessSqrt(2)
	guessSqrt(9)
	guessSqrt(612)
	guessSqrt(90000000000)
	guessSqrt(160000000000)
}