if x < 0 {
return sqrt(-x) + "i"
}
// 同 for 一样， if 语句可以在条件表达式前执行一个简单的语句。 该语句声明的变量作用域仅在 if 之内。
if v := math.Pow(x, n); v < lim {
return v
} else {
fmt.Printf("%g >= %g\n", v, lim)
}package main
import (
"fmt"
"runtime"
)
func main() {
fmt.Print("Go runs on ")
switch os := runtime.GOOS; os {
case "darwin":
fmt.Println("OS X.")
fallthrough
case "linux":
fmt.Println("Linux.")
default:
// freebsd, openbsd,
// plan9, windows...
fmt.Printf("%s.\n", os)
}
}
没有条件的switch
package main
import (
"fmt"
"time"
)
func main() {
t := time.Now()
switch {
case t.Hour() < 12:
fmt.Println("Good morning!")
case t.Hour() < 17:
fmt.Println("Good afternoon.")
default:
fmt.Println("Good evening.")
}
}
package main
import "fmt"
func main() {
defer fmt.Println("world")
fmt.Println("hello")
}
var p *inti := 42
p = &ifmt.Println(*p) // 通过指针 p 读取 i
*p = 21 // 通过指针 p 设置 ipackage main
import "fmt"
type Vertex struct
func main() {
v := Vertex{1, 2}
v1 = Vertex{1, 2} // 创建一个 Vertex 类型的结构体
v2 = Vertex{X: 1} // Y:0 被隐式地赋予
v3 = Vertex{} // X:0 Y:0
p = &Vertex{1, 2} // 创建一个 *Vertex 类型的结构体（指针）
v.X = 4
fmt.Println(v.X)
}
package main
import "fmt"
type Vertex struct
func main() {
v := Vertex{1, 2}
p := &v
//如果我们有一个指向结构体的指针 p，那么可以通过 (*p).X 来访问其字段 X。不过这么写太啰嗦了，所以语言也允许我们使用隐式间接引用，直接写 p.X 就可以。
p.X = 1e9
fmt.Println(v)
}
package main
import "fmt"
func main() {
var a [2]string
a[0] = "Hello"
a[1] = "World"
fmt.Println(a[0], a[1])
fmt.Println(a)
primes := [6]int{2, 3, 5, 7, 11, 13}
fmt.Println(primes)
}
package main
import "fmt"
func main() {
primes := [6]int{2, 3, 5, 7, 11, 13}
var s []int = primes[1:4]
fmt.Println(s)
}
package main
import "fmt"
func main() {
q := []int{2, 3, 5, 7, 11, 13}
fmt.Println(q)
r := []bool{true, false, true, true, false, true}
fmt.Println(r)
s := []struct {
i int
b bool
}{
{2, true},
{3, false},
{5, true},
{7, true},
{11, false},
{13, true},
}
fmt.Println(s)
}
忽略上下界
var a [10]inta[0:10]
a[:10]
a[0:]
a[:]package main
import "fmt"
func main() {
s := []int{2, 3, 5, 7, 11, 13}
printSlice(s)
// 截取切片使其长度为 0
s = s[:0]
printSlice(s)
// 拓展其长度
s = s[:4]
printSlice(s)
// 舍弃前两个值
s = s[2:]
printSlice(s)
}
func printSlice(s []int) {
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}
// 可以一次性添加多个元素
s = append(s, 2, 3, 4)package main
import "golang.org/x/tour/pic"
func Pic(dx, dy int) [][]uint8 {
var r [][]uint8
for x := 0; x < dx; x++ {
var temp []uint8
r = append(r, temp)
for y := 0; y < dy; y++ {
//r[x] = append(r[x], uint8((float64(x)math.Log(float64(y)))))
//r[x] = append(r[x], uint8(x%(y+1)))
//r[x] = append(r[x], uint8(x^y))
//r[x] = append(r[x], uint8(xy))
r[x] = append(r[x], uint8((x+y)/2))
}
}
return r
}
func main() {
pic.Show(Pic)
}
for range
package main
import "fmt"
type Vertex struct {
Lat, Long float64
}
var m map[string]Vertex
func main() {
m = make(map[string]Vertex)
m["Bell Labs"] = Vertex{
40.68433, -74.39967,
}
fmt.Println(m["Bell Labs"])
}
var m = map[string]Vertex{
"Bell Labs": Vertex{
40.68433, -74.39967,
},
"Google": Vertex{
37.42202, -122.08408,
},
}
var m = map[string]Vertex{
"Bell Labs": {40.68433, -74.39967},
"Google": {37.42202, -122.08408},
}
delete(m, key)elem, ok = m[key]package main
import (
"fmt"
"math"
)
func compute(fn func(float64, float64) float64) float64 {
return fn(3, 4)
}
func main() {
hypot := func(x, y float64) float64 {
return math.Sqrt(xx + yy)
}
fmt.Println(hypot(5, 12))
fmt.Println(compute(hypot))
fmt.Println(compute(math.Pow))
}
package main
import "fmt"
func adder() func(int) int {
sum := 0
return func(x int) int {
sum += x
return sum
}
}
func main() {
pos, neg := adder(), adder()
for i := 0; i < 10; i++ {
fmt.Println(
pos(i),
neg(-2*i),
)
}
}
0 0
1 -2
3 -6
6 -12
10 -20
15 -30
21 -42
28 -56
36 -72
45 -90 <div style="color: inherit; fill: inherit;">
<div style="display: flex;">
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