Golang - Udemy

Question 1

<p>Basic program</p>

Answer 1

package main
import “fmt”

func main(){ 
  fmt.Println("Helllo World......") 
} 

fmt.Println => accepts variadic parameters and returns multiple values

numBytes, err := fmt.Println(“hello’, 10, 20, “World”)

fmt.Println(a …args)(b, err)

Question 2

Keywords

Answer 2

break default func interface select
case defer go map struct
chan else goto package switch
const fallthrough if range type
continue for import return var

Question 3

Operators and Punctuations

Answer 3

+ & += &= && == != ( )
- | -= |= || < <= [ ]
* ^ *= ^= >= { }
/ &laquo_space; /= «= ++ = := , ;
% &raquo_space; %= &raquo_space;= – ! … . :
&^ &^=

Question 4

Variable Declaration

Answer 4

x := 10 => declares and assigns a variable
var x int => declares a variable and assign default

you cannot use := outside of function scope but you can use var

var x
func foo(){
  y := 20
}

x has package level scope
y has function level scope

Question 5

Default values for Primitive datatypes

Answer 5

Boolean   => false
int             => 0
float          => 0.0
string        => ""
pointers    => nil

Question 6

Variable Types

Answer 6

var x := 10
fmr.Printf(“%T”, x) ==> int

var s := “hello world”

s = x => error since you are going to assign int to string

Question 7

String Literals

Answer 7

s := hello world "how are you" ?

this will preserve the quotes and and carriage returns

Question 8

Creating your own Type

Answer 8

var a int
type foo int
var b foo

a  = 10
b = 20

a = b => error - unable to assign variable of one type to other

a = int(b) => works fine since we are Converting one type into another

Question 9

Finding about computer architecture

Answer 9

runtime. GOOS - os (linux)

runtime. GOARCH - architectures - 32/64

Question 10

String manipulations

Answer 10

s := “ABC”

for idx, v := range s{
fmt.Println(idx, v)
}

output
==
0 A
1 B
2 C

Question 11

Constants

Answer 11

const a = 10

const (
b = 20
c = 30
)

const k int = 200

Question 12

Packages

Answer 12

two types

• executable
• reusable package

executable packages

• needs to have package main declaration at the start
• needs to have func main()
• produces an executable at the end of the build step.

reusable package can have any name and it does not produce an executable at the end of the build process.

Question 13

Assigning value to a variable

Answer 13

var card string = “ace of spades”
card := “ace of spades”

both declarations are equivalent
:= is only used when you are creating a new variables and NOT when assigning values to an existing variable (you can use =)

Question 14

Functions

Answer 14

func () {

}

Question 15

Arrays

Answer 15

arrays - fixed size
slices - variable size

arr = [] string {"foo", "bar"}
arr = append(arr, "baz")

append does not modify the existing array
it creates a new array and assigns values back to arr

Question 16

Iterating over an array

Answer 16

nums = [] int {10, 20, 30, 40}

for i, num := range nums{
fmt.Prinln(i, num)
}

Question 17

Creating user defined types

Answer 17

type deck := [] string

we have declared a user defined typed which will accept an array of string

d := deck {“foo”, “bar”}

Question 18

Adding receivers (functions) to user defined types

Answer 18

type deck := [] string

func (d deck) print (){
   for _, card := range d{
      fmt.Println(card)
  }
}

d := deck{“foo”, “bar”}
d.print()

(d deck) is called receiver
any variable of type deck will not have access to function called print

receiver setups methods on variables that we create

func ( <var>) (){</var>

}</var>

Question 19

Structs

Answer 19

type person struct{
firstName string
}

adam := person{“Adam”}
sam := person{firstName: “Sam”}

Question 20

Structs within structs

Answer 20

type contactInfo struct{
zip string
}

type person struct{
firstName string
contact contactInfo
}

OR
type person struct{
  firstName string
  contactInfo
}

adam := person{“Adam”}
sam := person{firstName: “Sam”, contact: {
zip: 1234,
}}

Question 21

Print full struct Info

Answer 21

fmt.Printf(“%+v”, person)

Question 22

Structs with receiver functions

Answer 22

type person struct{
firstName string
contact contactInfo
}

func (p person) greet(){
  fmt.Println("Hello, my name is ", p.firstName)
}

adam := person{“Adam”}
adam.greet()

Question 23

Stucts in Go use pass by value !!!

Answer 23

change this to work

all functions in GO are pass by value i.e. it makes a copy of the object and manipulates it independently.

type person struct{
name string
}

func (p person) changeName(newName string){
  p.name = newName
}

alice = p{“alice”}

alice. changeName(“Foooooo”)
fmt. Println(alice.name) // alice ??????

funct (p *person) changeName(newName string){
p.name = newName
}

effectively GO will allow you to call the function with the variable and it does not required the pointer

i. e. pts = &alice
ptr. changeName(“Foooo”)

funct (p *person) changeName(newName string){
&p.name = newName
}

Question 24

Value types and Reference types

Answer 24

Value types

int, float, string, bool, structs

slices, maps, channels, pointers, functions

Question 25

Maps

Answer 25

rules
===
keys have to uniform types
values have to be of uniform types
they are pass by reference (so changes will reflect everywhere)

m := map [int]string{ 1: “Monday”, 2: “Tuesday”}
m := make (map[string]string)

m[“new_key”] := “new_value”
delete(m, 1)

Question 26

Interfaces

Answer 26

type bot interface{
greet() string
version() string
}

type englishBot struct{}
type spanishBot struct{}

func (b englishBot) greet() string{
  return "Hello"
}
func (b englishBot) version() string{
  return "2.0"
}

func (b spanishBot) greet() string {
  return "Hola"
}
func (b spanishBot) version() string{
  return "1.0"
}

//####
func sayHello(b bot){
  fmt.Println(b.greet())
}

func getVersion(b bot){
  fmt.Println(b.version())
}

func main(){
  alice := englishBot{}
  pablo := spanishBot{}

sayHello(alice)
getVersion(alice)

sayHello(pablo)
getVersion(pablo)
}