The Basic of Golang

GoBasic.go

/* 
Basic Go: Learn Go in 12 Minutes
ref: https://www.youtube.com/watch?v=C8LgvuEBraI
 */

package main

import (
	"fmt"
	"errors"
	"math"
)

func main() {
	fmt.Println("Hello, World!")

// Variable
	var x int		// default 0
	var x int = 5
	x := 5

	fmt.Println(x)		// result = 5

// Condition
	if x > 6 {
		fmt.Println("More than 6")
	} else if x < 2 {

	} else {

	}

// Array
	var a [5]int
	a := [5]int{5, 4, 3, 2, 1}
	a[2] = 7

	fmt.Println(a)		// result = [5 4 7 2 1]


// Slice
	a := []int{5, 4, 3, 2, 1}
	a = append(a, 13)


// Map
	vertices := make(map[string]int)

	vertices["triangle"] = 2
	vertices["square"] = 3
	vertices["dodecagon"] = 12

	delete(vertices, "square")

	fmt.Println(vertices)				// result = map[triangle:2 square:3 dodecagon:12]
	fmt.Println(vertices["triangle"])	// result = 2


// Loop
	for i := 0; i < 5; i++ {
		fmt.Println(i)		// result = 1 2 3 4 5
	}

	// While loop
	i := 0

	for i < 5 {
		fmt.Println(i)		// result = 1 2 3 4 5
		i++
	}

	// Loop over array
	arr := []string{"a", "b", "c"}

	for index, value := range arr {
		fmt.Println("index:", index, "value:", value)
		// result = index: 0 value: a
		//			index: 1 value: b
		//			index: 2 value: c
	}

	// Loop over map
	m := make(map[string]string)
	m["a"] = "alpha"
	m["b"] = "beta"

	for key, value := range m {
		fmt.Println("key:", key, "value:", value)
		// result = key: a value: alpha
		//			key: b value: beta
	}


// Calling method 
	/* 
	func sum(x int, y int) int {
		return x + y
	}
 	*/

	result := sum(2, 3)
	fmt.Println(result)		// result = 5


// Calling method with two return type
	/* 
	(Require import errors, math)
	func sqrt(x float64) (float64, error){
		if x < 0 {
			return 0, errors.New("Undefined for negative numbers")
		}

		return math.Sqrt(x), nil
	} 
	*/

	result, err := sqrt(16)

	if err != nil {
		fmt.Println(err)		// result = Undefined for negative numbers
	} else {
		fmt.Println(result)		// result = 4
	}


// struct is simillar with the object of Java
	/*
 	type person struct {
		name string
		age int
	} 
	*/

	p := person{name: "Jake", age: 23}
	fmt.Println(p)		// result = {Jake 23} 
	fmt.Println(p.age) // result = 23


// memory address, memory reference
	/* 
	(this function get a copy of i, the original i wont change)
	func inc(x int) {
		x++
	} 
	*/
	i := 7
	inc(i)
	fmt.Println(i)	// result = 7

	/* 
	(this function use memery referece, the original i will change)
	func inc(x *int) {
		*x++
	} 
	*/
	i := 7
	inc(&i)
	fmt.Println(i)	// result = 8

}