01-hello
package main
import (
"fmt"
)
func main() {
fmt.Println("Hello World")
}
02-var
package main
import (
"fmt"
"math"
_ "math"
)
func main() {
var a = "initial"
var b, c int = 1, 2
var d = true
var e float64
f := float32(e)
g := a + "apple"
fmt.Println(a, b, c, d, e, f) // initial 1 2 true 0 0
fmt.Println(g) //initialapple
const s string = "constant"
const h = 500000000
const i = 3e20 / h
fmt.Println(s, h, i, math.Sin(h), math.Sin(i))
}
03-for
package main
import (
"fmt"
)
func main() {
i := 1
for {
fmt.Println("loop")
break
}
fmt.Println("======")
for j := 1; j <= 10; j++ {
fmt.Println(j)
}
fmt.Println("======")
for n := 0; n < 5; n++ {
if n%2 == 0 {
continue
}
fmt.Println(n)
}
fmt.Println("======")
for i <= 3 {
fmt.Println(i)
i++
}
}
04-if
package main
import "fmt"
func main() {
if 7%2 == 0 {
fmt.Println("7 is even")
} else {
fmt.Println("7 is odd")
}
if 8%4 == 0 {
fmt.Println("8 is divisible by 4")
}
if num := 9; num < 0 {
fmt.Println(num, "is negative")
} else if num < 10 {
fmt.Println(num, "has 1 digit")
} else {
fmt.Println(num, "has multiple digits")
}
}
05-switch
package main
import (
"fmt"
"time"
)
func main() {
a := 2
switch a {
case 1:
fmt.Println("one")
case 2:
fmt.Println("two")
case 3:
fmt.Println("three")
case 4, 5:
fmt.Println("four or five")
default:
fmt.Println("other")
}
t := time.Now()
switch {
case t.Hour() < 12:
fmt.Println("It's before noon")
default:
fmt.Println("It's after noon")
}
}
06-array
package main
import (
"fmt"
)
func main() {
var a [5]int
a[4] = 100
fmt.Println("Gets:", a[4])
fmt.Println("len:", len(a))
b := [5]int{1, 2, 3, 4, 5}
fmt.Println(b)
var twoD [2][3]int
for i := 0; i < 2; i++ {
for j := 0; j < 3; j++ {
twoD[i][j] = i + j
}
}
fmt.Println("twoD:", twoD)
}
07-slice
package main
import "fmt"
func main() {
s := make([]string, 3)
s[0] = "a"
s[1] = "b"
s[2] = "c"
fmt.Println(s[2]) //c
fmt.Println(len(s)) //3
s = append(s, "d")
s = append(s, "e", "f")
fmt.Println(s) //[a,b,c,d,e,f]
c := make([]string, len(s))
copy(c, s)
fmt.Println(c) //[a,b,c,d,e,f]
fmt.Println(s[2:5])
fmt.Println(s[:5])
fmt.Println(s[2:])
good := []string{"g", "o", "o", "d"}
fmt.Println(good)
}
08-map
package main
import "fmt"
func main() {
m := make(map[string]int)
m["one"] = 1
m["two"] = 2
fmt.Println(m)
fmt.Println(len(m)) //map[one:1 two:2]
fmt.Println(m["one"]) //1
fmt.Println(m["two"]) //2
fmt.Println(m["unknow"]) //0
r, ok := m["unknow"]
fmt.Println(r, ok) //0 false
delete(m, "one")
m2 := map[string]int{"one": 1, "two": 2}
var m3 = map[string]int{"one": 1, "two": 2}
fmt.Println(m2, m3)
}
09-range
package main
import "fmt"
func main() {
nums := []int{1, 2, 3, 4, 5}
sum := 0
for i, num := range nums {
sum += num
if num == 2 {
fmt.Println("index:", i, "num:", num)
}
}
fmt.Println("sum:", sum)
m := map[string]string{"a": "A", "b": "B"}
for k, v := range m {
fmt.Println(k, v)
}
for k := range m {
fmt.Println("key:", k)
}
}
10-func
package main
import "fmt"
func add(a int, b int) int {
return a + b
}
func add2(a, b int) int {
return a + b
}
func exists(m map[string]string, k string) (v string, ok bool) {
v, ok = m[k]
return v, ok
}
func main() {
res := add(1, 2)
fmt.Println(res)
v, ok := exists(map[string]string{"a": "A"}, "a")
fmt.Println(v, ok) // A True
}
11-point
package main
import "fmt"
func add2(a int) {
a += 2
}
func add2ptr(a *int) {
*a += 2
}
func main() {
n := 5
add2(n)
fmt.Println(n)
add2ptr(&n)
fmt.Println(n)
}
12-struct
package main
import "fmt"
type user struct {
name string
password string
}
func main() {
a := user{name: "wang", password: "1024"}
b := user{"wang", "1024"}
c := user{name: "wang"}
c.password = "1024"
var d user
d.name = "wang"
d.password = "1024"
fmt.Println(a, b, c, d) // {wang 1024} {wang 1024} {wang 1024} {wang 1024}
fmt.Println(checkPassword(a, "haha")) // false
fmt.Println(checkPassword2(&a, "haha")) // false
}
func checkPassword(u user, password string) bool {
return u.password == password
}
func checkPassword2(u *user, password string) bool {
return u.password == password
}
13-struct-method
package main
import "fmt"
type user struct {
name string
password string
}
func (u user) checkPassword(password string) bool {
return u.password == password
}
func (u *user) resetPassword(password string) {
u.password = password
}
func main() {
a := user{name: "wang", password: "1024"}
a.resetPassword("2048")
fmt.Println(a.checkPassword("2048")) // true
}
14-error
package main
import (
"errors"
"fmt"
)
type user struct {
name string
password string
}
func findUser(users []user, name string) (v *user, err error) {
for _, u := range users {
if u.name == name {
return &u, nil
}
}
return nil, errors.New("Not Found")
}
func main() {
u, err := findUser([]user{
{"wang", "1024"}}, "wang")
if err != nil {
fmt.Println(err)
return
}
fmt.Println(u.name)
if u, err := findUser([]user{
{"wang", "1024"}}, "li"); err != nil {
fmt.Println(err) // not found
return
} else {
fmt.Println(u.name)
}
}
15-string
package main
import (
"fmt"
"strings"
)
func main() {
a := "hello"
fmt.Println(strings.Contains(a, "ll")) //true
fmt.Println(strings.Count(a, "l")) //2
fmt.Println(strings.HasPrefix(a, "he")) //true
fmt.Println(strings.Index(a, "ll")) //2
fmt.Println(strings.Join([]string{"he", "llo"}, "-")) //he-llo
fmt.Println(strings.Repeat(a, 2)) //hellohello
fmt.Println(strings.Replace(a, "e", "E", -1)) //hEllo
fmt.Println(strings.Split("a-b-c", "-")) //[a b c]
fmt.Println(strings.ToLower("HELLO")) //hello
fmt.Println(strings.ToUpper(a)) //HELLO
fmt.Println(len(a)) //5
fmt.Println(len("你好")) //6
}
16-fmt
package main
import "fmt"
type point struct {
x, y int
}
func main() {
s := "hello"
n := 123
p := point{1, 2}
fmt.Println(s, n) // hello 123
fmt.Println(p) // {1 2}
fmt.Printf("s=%v\n", s) // s=hello
fmt.Printf("n=%v\n", n) // n=123
fmt.Printf("p=%v\n", p) // p={1 2}
fmt.Printf("p=%+v\n", p) // p={x:1 y:2}
fmt.Printf("p=%#v\n", p) // p=main.point{x:1, y:2}
f := 3.141592653
fmt.Println(f) // 3.141592653
fmt.Printf("%.2f\n", f) // 3.14
}
17-json
package main
import (
"encoding/json"
"fmt"
)
type userInfo struct {
Name string
Age int `json:"age"`
Hobby []string
}
func main() {
a := userInfo{Name: "wang", Age: 18, Hobby: []string{"Golang", "TypeScript"}}
buf, err := json.Marshal(a)
if err != nil {
panic(err)
}
fmt.Println(buf) // [123 34 78 97...]
fmt.Println(string(buf)) // {"Name":"wang","age":18,"Hobby":["Golang","TypeScript"]}
buf, err = json.MarshalIndent(a, "", "\t")
if err != nil {
panic(err)
}
fmt.Println(string(buf))
var b userInfo
err = json.Unmarshal(buf, &b)
if err != nil {
panic(err)
}
fmt.Printf("%#v\n", b) // main.userInfo{Name:"wang", Age:18, Hobby:[]string{"Golang", "TypeScript"}}
}
18-time
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println(now) // 2022-03-27 18:04:59.433297 +0800 CST m=+0.000087933
t := time.Date(2022, 3, 27, 1, 25, 36, 0, time.UTC)
t2 := time.Date(2022, 3, 27, 2, 30, 36, 0, time.UTC)
fmt.Println(t) // 2022-03-27 01:25:36 +0000 UTC
fmt.Println(t.Year(), t.Month(), t.Day(), t.Hour(), t.Minute()) // 2022 March 27 1 25
fmt.Println(t.Format("2006-01-02 15:04:05")) // 2022-03-27 01:25:36
diff := t2.Sub(t)
fmt.Println(diff) // 1h5m0s
fmt.Println(diff.Minutes(), diff.Seconds()) // 65 3900
t3, err := time.Parse("2006-01-02 15:04:05", "2022-03-27 01:25:36")
if err != nil {
panic(err)
}
fmt.Println(t3 == t) // true
fmt.Println(now.Unix()) // 1648738080
}
19-strconv
package main
import (
"fmt"
"strconv"
)
func main() {
f, _ := strconv.ParseFloat("1.234", 64)
fmt.Println(f) // 1.234
n, _ := strconv.ParseInt("111", 10, 64)
fmt.Println(n) // 111
n, _ = strconv.ParseInt("0x1000", 0, 64)
fmt.Println(n) // 4096
n2, _ := strconv.Atoi("123")
fmt.Println(n2) // 123
n2, err := strconv.Atoi("AAA")
fmt.Println(n2, err) // 0 strconv.Atoi: parsing "AAA": invalid syntax
}
20-env
package main
import (
"fmt"
"os"
"os/exec"
)
func main() {
// go run example/20-env/main.go a b c d
fmt.Println(os.Args) // [/var/folders/8p/n34xxfnx38dg8bv_x8l62t_m0000gn/T/go-build3406981276/b001/exe/main a b c d]
fmt.Println(os.Getenv("PATH")) // /usr/local/go/bin...
fmt.Println(os.Setenv("AA", "BB"))
buf, err := exec.Command("grep", "127.0.0.1", "/etc/hosts").CombinedOutput()
if err != nil {
panic(err)
}
fmt.Println(string(buf)) // 127.0.0.1 localhost
}