Go语言基础: Switch语句、Arrays数组、Slices切片 详细教程案例

一. Switch语句

1. Default case

	finger := 6fmt.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

	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

	num := 75switch { // expression is omittedcase 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

	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

	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)fallthroughcase num < 100:fmt.Printf("%d is lesser than 100\n", num)fallthroughcase num < 200:fmt.Printf("%d is lesser than 200", num)
}

6. break for loop

	randloop:for {switch i := rand.Intn(100); {	// 100以内随机数case i%2 == 0:	// 能被2整除的ifmt.Printf("Generated even number %d", i)break randloop	// 必须添加break}}///  Generated even number 86

二. Arrays数组

	var a [3]int //	int array with length 3a[0] = 11a[1] = 12a[2] = 13b := [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 ff[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

    package mainimport "fmt"func changeLocal(num [5]int) {  num[0] = 22fmt.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 valuefmt.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

    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 52.00a := [...]float64{13.14, 14.13, 15.20, 21, 52}sum := float64(0)for i, v := range a { //range returns both the index and valuefmt.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

    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 52.00a := [...]float64{13.14, 14.13, 15.20, 21, 52}sum := float64(0)for i, v := range a { //range returns both the index and valuefmt.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

	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

	darr := [...]int{57, 89, 90, 82, 100, 78, 67, 69, 59}dslice := darr[2:5]               // 90 82 100fmt.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2numa := [3]int{78, 79, 80}nums1 := numa[:] //creates a slice which contains all elements of the arraynums2 := numa[:]fmt.Println("array before change 1", numa) // [78 79 80]nums1[0] = 100fmt.Println("array after modification to slice nums1", numa) // [100 79 80]nums2[1] = 101fmt.Println("array after modification to slice nums2", numa) //  [100 101 80]

3. Length and capacity of a slice

	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 6fruitslice = 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

	package mainimport (  "fmt")func main() {  i := make([]int, 5, 5)fmt.Println(i)}

5. Appending to a slice

	cars := []string{"Ferrari", "Honda", "Ford"}fmt.Println("cars:", cars, "has old length", len(cars), "and capacity", cap(cars)) //capacity of cars is 3cars = 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2var names []string	//zero value of a slice is nilif names == nil { // nil == Nonefmt.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

	func SubtactOne(numbers []int) {for i := range numbers { // i = index numbers = valuesfmt.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 slicefmt.Println("slice after function call", nos)  //  [2 3 4]}

7. Multidimensional slices

	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

	func Countries() []string {countries := []string{"China", "USA", "Singapore", "Germany", "India", "Australia"} // len:6, cap:6neededCountries := countries[:len(countries)-2]                                     // len:4, cap:6countriesCpy := make([]string, len(neededCountries))                                // len:4, cap:4copy(countriesCpy, neededCountries)                                                 // copy the make cap , values is neededCountriesreturn countriesCpy                                                                 // return list}func main() {countriesNeeded := Countries() // 赋值fmt.Println(countriesNeeded)   // [China USA Singapore Germany]}