文章目录
- [一. Switch语句](#一. Switch语句)
-
- [1. Default case](#1. Default case)
- [2. Multiple expressions in case](#2. Multiple expressions in case)
- [3. Expressionless switch](#3. Expressionless switch)
- [4. Fallthrough](#4. Fallthrough)
- [5. break](#5. break)
- [6. break for loop](#6. break for loop)
- [二. Arrays数组](#二. Arrays数组)
-
- [1. when arrays are passed to functions as parameters](#1. when arrays are passed to functions as parameters)
- [2. Iterating arrays using range](#2. Iterating arrays using range)
- [3.Multidimensional arrays 多维数组](#3.Multidimensional arrays 多维数组)
- [三. Slices切片](#三. Slices切片)
-
- [1. Creating a slice](#1. Creating a slice)
- [2. Modifying a slice](#2. Modifying a slice)
- [3. Length and capacity of a slice](#3. Length and capacity of a slice)
- [4. Creating a slice using make](#4. Creating a slice using make)
- [5. Appending to a slice](#5. Appending to a slice)
- [6. Passing a slice to a function](#6. Passing a slice to a function)
- [7. Multidimensional slices](#7. Multidimensional slices)
- [7. Memory Optimisation](#7. Memory Optimisation)
一. Switch语句
1. Default case
go
复制代码
finger := 6
fmt.Printf("Finger %d is ", finger)
switch finger {
case 1:
fmt.Println("Thumb")
case 2:
fmt.Println("Index")
case 3:
fmt.Println("Middle")
case 4: // 不能出现相同的数字
fmt.Println("Ring")
case 5:
fmt.Println("Pinky")
default: //default case 如果没有则执行默认
fmt.Println("incorrect finger number")
}
/// 输出： Finger 6 is incorrect finger number
2. Multiple expressions in case
go
复制代码
letter := "a"
fmt.Printf("Letter %s is a ", letter)
switch letter {
case "a", "b", "c", "d":
fmt.Println("Vowel")
default:
fmt.Println("No Vowel")
}
/// 输出 Letter a is a Vowel
3. Expressionless switch
go
复制代码
num := 75
switch { // expression is omitted
case num >= 0 && num <= 50:
fmt.Printf("%d is greater than 0 and less than 50", num)
case num >= 51 && num <= 100:
fmt.Printf("%d is greater than 51 and less than 100", num)
case num >= 101:
fmt.Printf("%d is greater than 100", num)
}
/// 75 is greater than 51 and less than 100
4. Fallthrough
go
复制代码
switch num := 25; {
case num < 50:
fmt.Printf("%d is lesser than 50\n", num)
fallthrough // 关键字
case num > 100: // 当这句是错误的 也会继续运行下一句
fmt.Printf("%d is greater than 100\n", num)
}
/// 25 is lesser than 50
/// 25 is greater than 100
5. break
go
复制代码
switch num := -7; {
case num < 50:
if num < 0 {
break // 小于0就被break了
}
fmt.Printf("%d is lesser than 50\n", num)
fallthrough
case num < 100:
fmt.Printf("%d is lesser than 100\n", num)
fallthrough
case num < 200:
fmt.Printf("%d is lesser than 200", num)
}
6. break for loop
go
复制代码
randloop:
for {
switch i := rand.Intn(100); { // 100以内随机数
case i%2 == 0: // 能被2整除的i
fmt.Printf("Generated even number %d", i)
break randloop // 必须添加break
}
}
/// Generated even number 86
二. Arrays数组
go
复制代码
var a [3]int // int array with length 3
a[0] = 11
a[1] = 12
a[2] = 13
b := [3]int{15, 16, 17} // 注意声明了int类型就不能是别的类型
c := [3]int{18}
d := [...]int{19, 20, 21}
e := [...]string{"USA", "China", "India", "Germany", "France"}
f := e // a copy of e is assigned to f
f[0] = "Singapore"
fmt.Println("a is ", a)
fmt.Println("b is ", b)
fmt.Println(b) // [15 16 17]
fmt.Println(a) // [11 12 13]
fmt.Println(c) // [18 0 0]
fmt.Println(d) // [19 20 21]
fmt.Println(e) // [USA China India Germany France]
fmt.Println(f) // [Singapore China India Germany France]
fmt.Println(len(f)) // 5 Length of an array
1. when arrays are passed to functions as parameters
go
复制代码
package main
import "fmt"
func changeLocal(num [5]int) {
num[0] = 22
fmt.Println("inside function ", num)
}
func main() {
num := [...]int{33, 44, 55, 66, 77}
fmt.Println("bebore passing to function", num)
changeLocal(num) // num is passing by value
fmt.Println("after passing to function", num)
}
// bebore passing to function [33 44 55 66 77]
// inside function [22 44 55 66 77]
// after passing to function [33 44 55 66 77]
2. Iterating arrays using range
go
复制代码
a := [...]float64{13.14, 14.13, 15.20, 21, 52}
for i := 0; i < len(a); i++ {
fmt.Printf("%d th element of a is %.2f\n", i, a[i])
}
// 0 th element of a is 13.14
// 1 th element of a is 14.13
// 2 th element of a is 15.20
// 3 th element of a is 21.00
// 4 th element of a is 52.00
a := [...]float64{13.14, 14.13, 15.20, 21, 52}
sum := float64(0)
for i, v := range a { //range returns both the index and value
fmt.Printf("%d the element of a is %.2f\n", i, v)
sum += v
}
fmt.Println("\nsum of all elements of a", sum)
// 0 the element of a is 13.14
// 1 the element of a is 14.13
// 2 the element of a is 15.20
// 3 the element of a is 21.00
// 4 the element of a is 52.00
// sum of all elements of a 115.47
3.Multidimensional arrays 多维数组
go
复制代码
a := [...]float64{13.14, 14.13, 15.20, 21, 52}
for i := 0; i < len(a); i++ {
fmt.Printf("%d th element of a is %.2f\n", i, a[i])
}
// 0 th element of a is 13.14
// 1 th element of a is 14.13
// 2 th element of a is 15.20
// 3 th element of a is 21.00
// 4 th element of a is 52.00
a := [...]float64{13.14, 14.13, 15.20, 21, 52}
sum := float64(0)
for i, v := range a { //range returns both the index and value
fmt.Printf("%d the element of a is %.2f\n", i, v)
sum += v
}
fmt.Println("\nsum of all elements of a", sum)
// 0 the element of a is 13.14
// 1 the element of a is 14.13
// 2 the element of a is 15.20
// 3 the element of a is 21.00
// 4 the element of a is 52.00
// sum of all elements of a 115.47
三. Slices切片
1. Creating a slice
go
复制代码
c := []int{555, 666, 777}
fmt.Println(c) // [555 666 777]
a := [5]int{76, 77, 78, 79, 80}
var b []int = a[1:4] // creates a slice from a[1] to a[3]
fmt.Println(b) // [77 78 79]
2. Modifying a slice
go
复制代码
darr := [...]int{57, 89, 90, 82, 100, 78, 67, 69, 59}
dslice := darr[2:5] // 90 82 100
fmt.Println("array before", darr) // array before [57 89 90 82 100 78 67 69 59]
for i := range dslice {
dslice[i]++ // 每一位数字+1
}
fmt.Println("array after", darr) // array after [57 89 91 83 101 78 67 69 59]
// 实例2
numa := [3]int{78, 79, 80}
nums1 := numa[:] //creates a slice which contains all elements of the array
nums2 := numa[:]
fmt.Println("array before change 1", numa) // [78 79 80]
nums1[0] = 100
fmt.Println("array after modification to slice nums1", numa) // [100 79 80]
nums2[1] = 101
fmt.Println("array after modification to slice nums2", numa) // [100 101 80]
3. Length and capacity of a slice
go
复制代码
fruitarray := [...]string{"apple", "orange", "grape", "mango", "water melon", "pine apple", "chikoo"}
fruitslice := fruitarray[1:3]
fmt.Printf("length of slice %d capacity %d", len(fruitslice), cap(fruitslice)) //length of fruitslice is 2 and capacity is 6
fruitslice = fruitslice[:cap(fruitslice)]
fmt.Println(fruitslice) // [orange grape mango water melon pine apple chikoo]
fmt.Println("After re-slicing length is", len(fruitslice), "and capacity is ", cap(fruitslice)) // After re-slicing length is 6 and capacity is 6
4. Creating a slice using make
go
复制代码
package main
import (
"fmt"
)
func main() {
i := make([]int, 5, 5)
fmt.Println(i)
}
5. Appending to a slice
go
复制代码
cars := []string{"Ferrari", "Honda", "Ford"}
fmt.Println("cars:", cars, "has old length", len(cars), "and capacity", cap(cars)) //capacity of cars is 3
cars = append(cars, "Toyota")
fmt.Println("cars:", cars, "has new length", len(cars), "and capacity", cap(cars)) //capacity of cars is doubled to 6 容量自动变大
// 实例2
var names []string //zero value of a slice is nil
if names == nil { // nil == None
fmt.Println("Slice is nil going to append")
names = append(names, "John", "Like", "Lisa")
fmt.Println("names contents:", names) // names contents: [John Like Lisa]
}
6. Passing a slice to a function
go
复制代码
func SubtactOne(numbers []int) {
for i := range numbers { // i = index numbers = values
fmt.Println(i, numbers)
numbers[i] -= 2 // 每次循环-2
}
}
func main() {
nos := []int{4, 5, 6}
fmt.Println("slice before function call", nos) // [4 5 6]
SubtactOne(nos) //function modifies the slice
fmt.Println("slice after function call", nos) // [2 3 4]
}
7. Multidimensional slices
go
复制代码
pls := [][]string{
{"C", "C--"},
{"Python"},
{"JavaScript"},
{"Go", "Rust"},
}
for _, v1 := range pls {
for _, v2 := range v1 {
fmt.Printf("%s", v2)
}
fmt.Printf("\n")
}
7. Memory Optimisation
go
复制代码
func Countries() []string {
countries := []string{"China", "USA", "Singapore", "Germany", "India", "Australia"} // len:6, cap:6
neededCountries := countries[:len(countries)-2] // len:4, cap:6
countriesCpy := make([]string, len(neededCountries)) // len:4, cap:4
copy(countriesCpy, neededCountries) // copy the make cap , values is neededCountries
return countriesCpy // return list
}
func main() {
countriesNeeded := Countries() // 赋值
fmt.Println(countriesNeeded) // [China USA Singapore Germany]
}