2.arrays

package main

import "fmt"

func main() {
	// Declare an array of five strings that is initialized
	// to its zero value.
	var strings [5]string
	strings[0] = "Apple"
	strings[1] = "Orange"
	strings[2] = "Banana"
	strings[3] = "Grape"
	strings[4] = "Plum"

	// Iterate over the array of strings.
	for index, fruit := range strings {
		fmt.Println(index, fruit)
	}

	// Declare an array of 4 integers that is initialized
	// with some values.
	numbers := [4]int{10, 20, 30, 40}

	for i := 0; i < len(numbers); i++ {
		fmt.Println(i, numbers[i])
	}
}

不同类型

//  Sample program to show how arrays of different sizes are
//  not of the same type.
//  示例程序演示不同大小的数组。
//  不是同一类型的。
package main

import "fmt"

func main() {
	// Declare an array of 5 integers that is initialized
	// to its zero value.
	var five [5]int

	// Declare an array of 4 integers that is initialized
	// with some values.
	four := [4]int{10, 20, 30, 40}

	// Assign one array to the other
	five = four

	// ./example2.go:21: cannot use four (type [4]int) as type [5]int in assignment

	fmt.Println(four)
	fmt.Println(five)
}

数组大小决定其寻址能力

// All material is licensed under the Apache License Version 2.0, January 2004
// http://www.apache.org/licenses/LICENSE-2.0

// Sample program to show how the behavior of the for range and
// how memory for an array is contiguous.
package main

import "fmt"

func main() {
	// Declare an array of 5 strings initialized with values.
	five := [5]string{"Annie", "Betty", "Char", "Doug", "Edra"}

	// Iterate over the array displaying the value and
	// address of each element.
	for i, v := range five {
		fmt.Printf("value[%s] Address[%p] IndexAddr[%p]\n", v, &v, &five[i])
	}
	/*
	 数组地址没有改变，但是下标地址一直改变
		value[Annie] Address[0xc42000e1d0] IndexAddr[0xc4200840f0]
		value[Betty] Address[0xc42000e1d0] IndexAddr[0xc420084100]
		value[Char] Address[0xc42000e1d0] IndexAddr[0xc420084110]
		value[Doug] Address[0xc42000e1d0] IndexAddr[0xc420084120]
		value[Edra] Address[0xc42000e1d0] IndexAddr[0xc420084130]

	*/
}

值传递

// Sample program to show how the for range has both value and pointer semantics.
// 示例程序，以显示for range如何具有值和指针语义。
package main

import "fmt"

func main() {

	// Using the pointer semantic form of the for range.
	five := [5]string{"Annie", "Betty", "Charley", "Doug", "Edward"}
	fmt.Printf("Bfr[%s] : ", five[1])

	for i := range five {
		five[1] = "Jack"
		if i == 1 {
			fmt.Printf("Aft[%s]\n", five[1])
		}
	}

	// Using the value semantic form of the for range.
	five = [5]string{"Annie", "Betty", "Charley", "Doug", "Edward"}
	fmt.Printf("Bfr[%s] : ", five[1])
	for i, v := range five { // 块级别作用域，
		five[1] = "Jack"

		if i == 1 {
			fmt.Printf("v[%s]\n", v)
		}
	}

	// Using the value semantic form of the for range but with pointer
	// semantic access. DON'T DO THIS.

	five = [5]string{"Annie", "Betty", "Charley", "Doug", "Edward"}
	fmt.Printf("Bfr[%s] : ", five[1])

	for i, v := range &five { // 指针值 最终取到的是值
		five[1] = "Jack"

		if i == 1 {
			fmt.Printf("v[%s]\n", v)
		}
	}

	/* 以上示例说明go是传值，值复制（拷贝副本）*/

}

/*
Bfr[Betty] : Aft[Jack]
Bfr[Betty] : v[Betty]
Bfr[Betty] : v[Jack]
*/

练习

// All material is licensed under the Apache License Version 2.0, January 2004
// http://www.apache.org/licenses/LICENSE-2.0

// Declare an array of 5 strings with each element initialized to its zero value.
//
// Declare a second array of 5 strings and initialize this array with literal string
// values. Assign the second array to the first and display the results of the first array.
// Display the string value and address of each element.
package main

import (
	"fmt"
)

// Add imports.

func main() {

	// Declare an array of 5 strings set to its zero value.
	var fivestring [5]string
	fmt.Printf(fivestring[0])

	// Declare an array of 5 strings and pre-populate it with names.
	five_s := [5]string{"1s", "2s", "3s", "4s", "5s"}
	println(five_s[0])

	// Assign the populated array to the array of zero values. 将已填充的数组分配为零值数组。
	var name [5]string
	name = five_s
	println(name[0])
	fmt.Println("\n")
	fmt.Println("\n")

	// Iterate over the first array declared.
	// Display the string value and address of each element.

	for i, v := range name {
		fmt.Println(v, &name[i])
	}
}

/*
1s 0xc4200840f0
2s 0xc420084100
3s 0xc420084110
4s 0xc420084120
5s 0xc420084130


*/