A tour to go Exercise

go_exercise.go

/*
https://tour.golang.org/flowcontrol/8
http://go-tour-zh.appspot.com/flowcontrol/8
*/

/* Exercise: Loops and Functions #43 */
/* Exercise: Loops and Functions #43 */
package main

import (
	"fmt"
	"math"
)

func Abs(x float64) float64 {
	if x < 0 {
		x = -x
	}
	return x
}

func Sqrt(x float64) (float64, int) {

	z := float64(1)
	tmp := float64(0)
	times := int(0)

	for {
		times++
		z = z - (z*z-x)/(2*z)
		if Abs(z-tmp) < 1e-15 {
			//fmt.Printf("loop %d times\n", times)
			break
		}
		tmp = z
	}

	return z, times
}

func main() {

	for i := float64(1); i < 10; i++ {
		attempt, times := Sqrt(i)

		expected := math.Sqrt(i)

		fmt.Printf("sqrt %g times %d --- attempt= %g (expected = %g) error = %g\n", i, times, attempt, expected, Abs(attempt-expected))
	}

}
/* console outprint */
/*
sqrt 1 times 2 --- attempt= 1 (expected = 1) error = 0
sqrt 2 times 6 --- attempt= 1.414213562373095 (expected = 1.4142135623730951) error = 2.220446049250313e-16
sqrt 3 times 6 --- attempt= 1.7320508075688774 (expected = 1.7320508075688772) error = 2.220446049250313e-16
sqrt 4 times 7 --- attempt= 2 (expected = 2) error = 0
sqrt 5 times 7 --- attempt= 2.23606797749979 (expected = 2.23606797749979) error = 0
sqrt 6 times 7 --- attempt= 2.449489742783178 (expected = 2.449489742783178) error = 0
sqrt 7 times 7 --- attempt= 2.6457513110645907 (expected = 2.6457513110645907) error = 0
sqrt 8 times 7 --- attempt= 2.82842712474619 (expected = 2.8284271247461903) error = 4.440892098500626e-16
sqrt 9 times 7 --- attempt= 3 (expected = 3) error = 0
*/