"A Tour of Go"

Errors.go

/*
Exercise: Errors

Copy your Sqrt function from the earlier exercises and modify it to return an error value.

Sqrt should return a non-nil error value when given a negative number, as it doesn't support complex numbers.

Create a new type

type ErrNegativeSqrt float64
and make it an error by giving it a

func (e ErrNegativeSqrt) Error() string
method such that ErrNegativeSqrt(-2).Error() returns "cannot Sqrt negative number: -2".

Note: a call to fmt.Print(e) inside the Error method will send the program into an infinite loop. You can avoid this by converting e first: fmt.Print(float64(e)). Why?

Change your Sqrt function to return an ErrNegativeSqrt value when given a negative number.
*/
package main

import (
    "fmt"
    "math"
)

type ErrNegativeSqrt float64

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


func Sqrt(x float64) (float64, error) {
    if x<0.0 {
    	return 0,ErrNegativeSqrt(x)
    }
    
    z := 1.0
    
	for i := 1; i < 100; i++ {
		z = z - ((math.Pow(z, 2) - x) / (2 * x))
	}
	return z,nil
}

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