example of pointer's usage. In general, all methods on a given type should have either value or pointer receivers, but not a mixture of both.

pointer.go

package main

import (
	"fmt"
)

type counter struct {
	I int
}

func (c counter) Plus() int {
	return c.I
}

func (c *counter) Minus() int {
	c.I--

	return c.I
}

func plus(c counter) int {
	return c.I
}

func minus(c *counter) int {
	c.I--

	return c.I
}

func main() {
	c := counter{I: 10}
	fmt.Println(c.Minus())
	fmt.Println(c.Plus())

	c2 := &counter{I: 10}
	fmt.Println(minus(c2))
	fmt.Println(plus(*c2))

	c3 := counter{I: 10}
	fmt.Println(minus(&c3))
	fmt.Println(plus(c3))

}