go学习代码

[TOC]

声明变量

package main

import "fmt"

func main() {

    //1.
    var a int = 520
    fmt.Println(a)

    //2.
    b := 1314
    fmt.Println(b)

    //3
    var (
        c int = 959
        d int = 244
    )
    fmt.Println(c + d)

    //4
    var e = 2023
    fmt.Println(e)
}

常量(模拟枚举)

package main

import "fmt"

//模拟枚举
/*
iota,每行递增
*/
const (
    A = iota
    B
    C
    D = 20
    E
    F = iota
    G = "adh"
)

func main() {
    //设置const常量
    //不能使用自动类型推导
    const a int = 10
    const b = 20
    fmt.Println(a)
    fmt.Println(b)
    fmt.Println(A)
    fmt.Println(F)
    fmt.Println(G)
}

多返回值(三种)

func add(a int, b int) (int, int, int) {
    return a, b, a + b
}

func add1(a int, b int) (c, d int) {
    return
}

func add2(a int, b int) (sum int) {
    sum = a + b
    return sum
}

func main() {
    a, b, sum := add(1, 4)
    fmt.Printf("%v+%v=%v", a, b, sum)

    c, d := add1(1, 2)
    fmt.Println(c, d)

    sum1 := add2(2, 4)
    fmt.Println(sum1)

}

切片的声明

func main() {
    //直接声明并且初始化
    ints := []int{1, 2, 3}
    for _, v := range ints {
        fmt.Println(v)
    }

    //先声明再创建空间
    var ints2 []int
    ints2 = make([]int, 2)
    for _, v := range ints2 {
        fmt.Println(v)
    }
    fmt.Println(ints)

    ints3 := [3]int{1, 2, 4}
    fmt.Println(ints3)

}

容量和长度

//容量和长度

func main() {
    ints := make([]int, 2)
    fmt.Printf("len:%d   cap:%d   ints:%v", len(ints), cap(ints), ints)
    ints = append(ints, 1)
    fmt.Printf("len:%d   cap:%d   ints:%v", len(ints), cap(ints), ints)
    ints = append(ints, 2)
    ints = append(ints, 3)
    fmt.Printf("len:%d   cap:%d   ints:%v", len(ints), cap(ints), ints)

}	

数组，切片的截取

//声明切片的几个方法

func main() {
    ints := []int{1, 2, 3, 4, 5}

    fmt.Println(ints[0:2]) //[0,2)

    fmt.Println(ints[0:len(ints)]) //打印全部的切片

    ints2 := [5]int{1, 2, 3, 4, 5}
    fmt.Println(ints2)
    fmt.Println(ints2[0:2])  //数组的=也可以截取

}

map的声明

// map的声明
func main() {
    //第一种方式
    map1 := map[string]int{
        "one":   1,
        "two":   2,
        "three": 3,
    }
    fmt.Println(map1)

    //第二种形式
    var map2 map[string]int = make(map[string]int, 4)
    fmt.Println(map2)

    //第三种方式
    map3 := make(map[string]int, 6)
    fmt.Println(map3)
}

delete的使用

func main() {
    maps := map[string]int{
        "one": 1,
        "two": 2,
    }
    v, isHave := maps["two"]
    if isHave == true {
        fmt.Println(v)
    }

    delete(maps, "two")

    v, isHave = maps["two"]

    if isHave != true {
        fmt.Println("this is no value")
    }

}