Go by Example

网页地址Go by Example 中文版

Github仓库地址mmcgrana/gobyexample：按示例进行

HelloWorld

package main

import (
	"fmt"
)

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

Hello World 

值

package main

import (
	"fmt"
)

func main() {
	fmt.Println("go" + "lang")
	fmt.Println("1+1=", 1+1)
	fmt.Println("7.0/3.0", 7.0/3.0)

	fmt.Println(true && false)
	fmt.Println(true || false)
	fmt.Println(!true)
}

golang
1+1= 2
7.0/3.0 2.3333333333333335
false
true
false

变量

package main

import "fmt"

func main() {
	var a = "initial"
	fmt.Println(a)

	var b, c int = 1, 2
	fmt.Println(b, c)
	var d = true
	fmt.Println(d)
	var e int
	fmt.Println(e)
	f := "short"
	fmt.Println(f)
}

 initial
1 2
true
0
short

常量

package main

import (
	"fmt"
	"math"
)

const s string = "constant"

func main() {
	fmt.Println(s)

	const n = 500000000

	const d = 3e20 / n
	fmt.Println(d)
	fmt.Println(int64(d))
	fmt.Println(math.Sin(n))
}

 constant
6e+11
600000000000
-0.28470407323754404

For循环

package main

import "fmt"

func main() {
	i := 1
	for i <= 3 {
		fmt.Println(i)
		i++
	}

	for j := 7; j <= 9; j++ {
		fmt.Println(j)
	}
	for {
		fmt.Println("loop")
		break
	}
	for n := 0; n <= 5; n++ {
		if n%2 == 0 {
			continue
		}
		fmt.Println(n)
	}
}

1
2
3
7
8
9
loop
1
3
5 

 If/Else分支

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")
	}

}

 7 is odd
8 is divisible by 4
9 has 1 digit

Switch分支结构

package main

import (
	"fmt"
	"time"
)

func main() {
	i := 2
	fmt.Print("write ", i, " as ")
	switch i {
	case 1:
		fmt.Println("1")
	case 2:
		fmt.Println("2")
	case 3:
		fmt.Println("3")
	}

	switch time.Now().Weekday() {
	case time.Saturday, time.Sunday:
		fmt.Println("It's the weekend")
	default:
		fmt.Println("It's a weekday")
	}

	t := time.Now()
	switch {
	case t.Hour() < 12:
		fmt.Println("It's before noon")
	default:
		fmt.Println("It's after noon")
	}

	// 独立出来的类型判断函数
	whatAmI := func(i interface{}) {
		switch t := i.(type) {
		case bool:
			fmt.Println("I'm a bool")
		case int:
			fmt.Println("I'm an int")
		default:
			fmt.Printf("Don't know type %T\n", t)
		}
	}

	whatAmI(true)
	whatAmI(1)
	whatAmI("hey")
}

 write 2 as 2
It's the weekend
It's after noon
I'm a bool
I'm an int
Don't know type string

 数组

package main

import "fmt"

func main() {

	var a [5]int
	fmt.Println("emp:", a)

	a[4] = 100
	fmt.Println("set:", a)
	fmt.Println("get:", a[4])

	fmt.Println("len:", len(a))

	b := [5]int{1, 2, 3, 4, 5}
	fmt.Println("dcl:", 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("2d: ", twoD)
}

 emp: [0 0 0 0 0]
set: [0 0 0 0 100]
get: 100
len: 5
dcl: [1 2 3 4 5]
2d:  [[0 1 2] [1 2 3]]

切片

package main

import "fmt"

func main() {

    s := make([]string, 3)
    fmt.Println("emp:", s)

    s[0] = "a"
    s[1] = "b"
    s[2] = "c"
    fmt.Println("set:", s)
    fmt.Println("get:", s[2])

    fmt.Println("len:", len(s))

    s = append(s, "d")
    s = append(s, "e", "f")
    fmt.Println("apd:", s)

    c := make([]string, len(s))
    copy(c, s)
    fmt.Println("cpy:", c)

    l := s[2:5]
    fmt.Println("sl1:", l)

    l = s[:5]
    fmt.Println("sl2:", l)

    l = s[2:]
    fmt.Println("sl3:", l)

    t := []string{"g", "h", "i"}
    fmt.Println("dcl:", t)

    twoD := make([][]int, 3)
    for i := 0; i < 3; i++ {
        innerLen := i + 1
        twoD[i] = make([]int, innerLen)
        for j := 0; j < innerLen; j++ {
            twoD[i][j] = i + j
        }
    }
    fmt.Println("2d: ", twoD)
}

 emp: [  ]
set: [a b c]
get: c
len: 3
apd: [a b c d e f]
cpy: [a b c d e f]
sl1: [c d e]
sl2: [a b c d e]
sl3: [c d e f]
dcl: [g h i]
2d:  [[0] [1 2] [2 3 4]]