633 lines
15 KiB
Go
633 lines
15 KiB
Go
/*
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03-for-loops.go - Go 语言 for 循环详解
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学习目标：
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1. 掌握 for 循环的各种形式
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2. 理解 break 和 continue 的使用
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3. 学会使用标签控制嵌套循环
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4. 了解无限循环的写法
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5. 掌握循环的实际应用场景
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知识点：
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- 传统 for 循环
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- while 风格的 for 循环
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- 无限循环
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- break 和 continue
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- 标签 (label)
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- 嵌套循环
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- 循环优化技巧
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*/
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package main
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import (
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"fmt"
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"math/rand"
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"time"
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)
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func main() {
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fmt.Println("=== Go 语言 for 循环详解 ===\n")
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// 演示传统 for 循环
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demonstrateTraditionalFor()
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// 演示 while 风格的 for 循环
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demonstrateWhileStyleFor()
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// 演示无限循环
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demonstrateInfiniteLoop()
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// 演示 break 和 continue
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demonstrateBreakContinue()
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// 演示嵌套循环和标签
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demonstrateNestedLoopsAndLabels()
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// 演示循环的实际应用
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demonstratePracticalExamples()
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// 演示循环优化技巧
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demonstrateOptimizationTips()
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}
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// demonstrateTraditionalFor 演示传统 for 循环
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func demonstrateTraditionalFor() {
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fmt.Println("1. 传统 for 循环:")
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// 基本的 for 循环
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fmt.Printf(" 基本 for 循环 (0-4):\n")
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for i := 0; i < 5; i++ {
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fmt.Printf(" i = %d\n", i)
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}
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// 倒序循环
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fmt.Printf(" 倒序循环 (5-1):\n")
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for i := 5; i > 0; i-- {
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fmt.Printf(" i = %d\n", i)
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}
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// 步长为 2 的循环
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fmt.Printf(" 步长为 2 的循环:\n")
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for i := 0; i <= 10; i += 2 {
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fmt.Printf(" i = %d\n", i)
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}
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// 多个变量的循环
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fmt.Printf(" 多变量循环:\n")
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for i, j := 0, 10; i < j; i, j = i+1, j-1 {
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fmt.Printf(" i = %d, j = %d\n", i, j)
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}
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// 计算累加和
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sum := 0
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for i := 1; i <= 10; i++ {
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sum += i
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}
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fmt.Printf(" 1到10的累加和: %d\n", sum)
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// 计算阶乘
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factorial := 1
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n := 5
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for i := 1; i <= n; i++ {
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factorial *= i
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}
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fmt.Printf(" %d的阶乘: %d\n", n, factorial)
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fmt.Println()
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}
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// demonstrateWhileStyleFor 演示 while 风格的 for 循环
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func demonstrateWhileStyleFor() {
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fmt.Println("2. while 风格的 for 循环:")
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fmt.Printf(" Go 没有 while 关键字，使用 for 代替\n")
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// 模拟 while 循环
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fmt.Printf(" 模拟 while 循环:\n")
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count := 0
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for count < 5 {
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fmt.Printf(" count = %d\n", count)
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count++
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}
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// 条件判断循环
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fmt.Printf(" 条件判断循环 (猜数字):\n")
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target := 7
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guess := 1
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attempts := 0
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for guess != target {
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attempts++
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fmt.Printf(" 第 %d 次猜测: %d", attempts, guess)
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if guess < target {
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fmt.Printf(" (太小了)\n")
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guess += 2
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} else {
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fmt.Printf(" (太大了)\n")
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guess--
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}
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}
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fmt.Printf(" 恭喜！第 %d 次猜中了: %d\n", attempts+1, guess)
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// 读取用户输入直到满足条件
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fmt.Printf(" 模拟输入验证:\n")
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password := ""
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attempts = 0
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correctPassword := "123456"
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// 模拟用户输入
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inputs := []string{"111", "222", "123456"}
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for password != correctPassword && attempts < 3 {
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password = inputs[attempts] // 模拟用户输入
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attempts++
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fmt.Printf(" 第 %d 次输入密码: %s", attempts, password)
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if password == correctPassword {
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fmt.Printf(" (正确)\n")
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} else {
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fmt.Printf(" (错误)\n")
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}
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}
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if password == correctPassword {
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fmt.Printf(" 登录成功！\n")
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} else {
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fmt.Printf(" 登录失败，超过最大尝试次数\n")
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}
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fmt.Println()
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}
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// demonstrateInfiniteLoop 演示无限循环
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func demonstrateInfiniteLoop() {
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fmt.Println("3. 无限循环:")
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fmt.Printf(" 无限循环的写法: for { ... }\n")
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fmt.Printf(" 通常配合 break 使用\n")
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// 无限循环示例1: 服务器主循环模拟
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fmt.Printf(" 示例1 - 服务器主循环模拟:\n")
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requestCount := 0
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for {
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requestCount++
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fmt.Printf(" 处理第 %d 个请求\n", requestCount)
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// 模拟处理请求
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if requestCount >= 3 {
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fmt.Printf(" 服务器关闭\n")
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break
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}
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}
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// 无限循环示例2: 菜单系统
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fmt.Printf(" 示例2 - 菜单系统模拟:\n")
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menuOptions := []string{"查看余额", "转账", "退出"}
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choice := 0
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for {
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fmt.Printf(" 请选择操作:\n")
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for i, option := range menuOptions {
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fmt.Printf(" %d. %s\n", i+1, option)
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}
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// 模拟用户选择
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choice = (choice % 3) + 1
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fmt.Printf(" 用户选择: %d\n", choice)
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switch choice {
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case 1:
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fmt.Printf(" 当前余额: 1000元\n")
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case 2:
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fmt.Printf(" 转账功能暂未开放\n")
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case 3:
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fmt.Printf(" 谢谢使用，再见！\n")
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return // 或者使用 break
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}
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// 为了演示，只循环一次
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break
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}
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fmt.Println()
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}
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// demonstrateBreakContinue 演示 break 和 continue
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func demonstrateBreakContinue() {
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fmt.Println("4. break 和 continue:")
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// break 示例
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fmt.Printf(" break - 跳出循环:\n")
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for i := 0; i < 10; i++ {
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if i == 5 {
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fmt.Printf(" 遇到 %d，跳出循环\n", i)
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break
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}
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fmt.Printf(" i = %d\n", i)
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}
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// continue 示例
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fmt.Printf(" continue - 跳过当前迭代:\n")
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for i := 0; i < 10; i++ {
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if i%2 == 0 {
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continue // 跳过偶数
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}
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fmt.Printf(" 奇数: %d\n", i)
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}
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// 实际应用：处理数据时跳过无效值
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fmt.Printf(" 实际应用 - 处理数据跳过无效值:\n")
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data := []int{1, -2, 3, 0, 5, -6, 7, 8, 0, 9}
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sum := 0
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validCount := 0
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for i, value := range data {
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if value <= 0 {
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fmt.Printf(" 跳过无效值 data[%d] = %d\n", i, value)
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continue
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}
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sum += value
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validCount++
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fmt.Printf(" 处理有效值 data[%d] = %d\n", i, value)
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}
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fmt.Printf(" 有效数据个数: %d，总和: %d，平均值: %.2f\n",
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validCount, sum, float64(sum)/float64(validCount))
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// 查找第一个满足条件的元素
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fmt.Printf(" 查找第一个大于 50 的数:\n")
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numbers := []int{10, 25, 30, 55, 60, 75}
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found := false
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for i, num := range numbers {
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fmt.Printf(" 检查 numbers[%d] = %d\n", i, num)
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if num > 50 {
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fmt.Printf(" 找到第一个大于 50 的数: %d\n", num)
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found = true
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break
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}
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}
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if !found {
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fmt.Printf(" 没有找到大于 50 的数\n")
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}
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fmt.Println()
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}
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// demonstrateNestedLoopsAndLabels 演示嵌套循环和标签
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func demonstrateNestedLoopsAndLabels() {
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fmt.Println("5. 嵌套循环和标签:")
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// 基本嵌套循环
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fmt.Printf(" 基本嵌套循环 - 乘法表:\n")
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for i := 1; i <= 3; i++ {
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for j := 1; j <= 3; j++ {
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fmt.Printf(" %d × %d = %d\n", i, j, i*j)
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}
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}
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// 使用标签控制嵌套循环
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fmt.Printf(" 使用标签控制嵌套循环:\n")
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outer:
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for i := 1; i <= 3; i++ {
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for j := 1; j <= 3; j++ {
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fmt.Printf(" i=%d, j=%d\n", i, j)
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if i == 2 && j == 2 {
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fmt.Printf(" 在 i=2, j=2 时跳出外层循环\n")
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break outer
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}
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}
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}
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// 标签 continue 示例
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fmt.Printf(" 标签 continue 示例:\n")
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outerContinue:
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for i := 1; i <= 3; i++ {
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fmt.Printf(" 外层循环 i = %d\n", i)
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for j := 1; j <= 3; j++ {
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if i == 2 && j == 2 {
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fmt.Printf(" 在 i=2, j=2 时跳过外层循环的当前迭代\n")
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continue outerContinue
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}
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fmt.Printf(" 内层循环 j = %d\n", j)
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}
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fmt.Printf(" 外层循环 i = %d 结束\n", i)
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}
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// 矩阵搜索示例
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fmt.Printf(" 矩阵搜索示例:\n")
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matrix := [][]int{
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{1, 2, 3},
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{4, 5, 6},
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{7, 8, 9},
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}
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target := 5
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found := false
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search:
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for i := 0; i < len(matrix); i++ {
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for j := 0; j < len(matrix[i]); j++ {
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fmt.Printf(" 检查 matrix[%d][%d] = %d\n", i, j, matrix[i][j])
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if matrix[i][j] == target {
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fmt.Printf(" 找到目标值 %d 在位置 [%d][%d]\n", target, i, j)
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found = true
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break search
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}
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}
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}
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if !found {
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fmt.Printf(" 未找到目标值 %d\n", target)
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}
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fmt.Println()
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}
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// demonstratePracticalExamples 演示循环的实际应用
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func demonstratePracticalExamples() {
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fmt.Println("6. 循环的实际应用:")
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// 示例1: 数组/切片处理
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fmt.Printf(" 示例1 - 数组处理:\n")
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scores := []int{85, 92, 78, 96, 88, 73, 91}
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// 计算平均分
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total := 0
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for _, score := range scores {
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total += score
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}
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average := float64(total) / float64(len(scores))
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fmt.Printf(" 平均分: %.2f\n", average)
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// 找出最高分和最低分
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maxScore, minScore := scores[0], scores[0]
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for _, score := range scores {
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if score > maxScore {
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maxScore = score
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}
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if score < minScore {
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minScore = score
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}
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}
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fmt.Printf(" 最高分: %d，最低分: %d\n", maxScore, minScore)
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// 统计及格人数
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passCount := 0
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for _, score := range scores {
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if score >= 80 {
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passCount++
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}
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}
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fmt.Printf(" 及格人数: %d/%d\n", passCount, len(scores))
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// 示例2: 字符串处理
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fmt.Printf(" 示例2 - 字符串处理:\n")
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text := "Hello, 世界! 123"
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// 统计字符类型
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letters, digits, others := 0, 0, 0
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for _, char := range text {
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switch {
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case (char >= 'a' && char <= 'z') || (char >= 'A' && char <= 'Z') || char > 127:
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letters++
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case char >= '0' && char <= '9':
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digits++
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default:
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others++
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}
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}
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fmt.Printf(" 字符串: \"%s\"\n", text)
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fmt.Printf(" 字母: %d，数字: %d，其他: %d\n", letters, digits, others)
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// 示例3: 数学计算
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fmt.Printf(" 示例3 - 数学计算 (斐波那契数列):\n")
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n := 10
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fmt.Printf(" 前 %d 个斐波那契数:\n", n)
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a, b := 0, 1
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for i := 0; i < n; i++ {
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fmt.Printf(" F(%d) = %d\n", i, a)
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a, b = b, a+b
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}
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// 示例4: 模拟游戏
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fmt.Printf(" 示例4 - 简单猜数字游戏:\n")
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rand.Seed(time.Now().UnixNano())
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secretNumber := rand.Intn(10) + 1
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maxAttempts := 3
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// 模拟玩家猜测
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guesses := []int{5, 8, secretNumber}
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for attempt := 1; attempt <= maxAttempts; attempt++ {
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guess := guesses[attempt-1] // 模拟用户输入
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fmt.Printf(" 第 %d 次猜测: %d", attempt, guess)
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if guess == secretNumber {
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fmt.Printf(" - 恭喜你猜对了！\n")
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break
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} else if guess < secretNumber {
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fmt.Printf(" - 太小了\n")
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} else {
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fmt.Printf(" - 太大了\n")
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}
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if attempt == maxAttempts {
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fmt.Printf(" 游戏结束！正确答案是: %d\n", secretNumber)
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}
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}
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// 示例5: 数据验证
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fmt.Printf(" 示例5 - 批量数据验证:\n")
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emails := []string{
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"user@example.com",
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"invalid-email",
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"test@domain.org",
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"@invalid.com",
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"valid@test.net",
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}
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validEmails := 0
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for i, email := range emails {
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isValid := validateEmail(email)
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fmt.Printf(" 邮箱 %d: %-20s - ", i+1, email)
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if isValid {
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fmt.Printf("有效\n")
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validEmails++
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} else {
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fmt.Printf("无效\n")
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}
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}
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fmt.Printf(" 有效邮箱数量: %d/%d\n", validEmails, len(emails))
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fmt.Println()
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}
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// demonstrateOptimizationTips 演示循环优化技巧
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func demonstrateOptimizationTips() {
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fmt.Println("7. 循环优化技巧:")
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// 技巧1: 减少重复计算
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fmt.Printf(" 技巧1 - 减少重复计算:\n")
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data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
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// 不好的写法：每次都计算 len(data)
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fmt.Printf(" 不推荐的写法 (每次计算长度):\n")
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for i := 0; i < len(data); i++ {
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// len(data) 在每次迭代时都会被调用
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fmt.Printf(" data[%d] = %d\n", i, data[i])
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if i >= 2 { // 为了演示，只显示前几个
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break
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}
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}
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// 好的写法：预先计算长度
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fmt.Printf(" 推荐的写法 (预先计算长度):\n")
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length := len(data)
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for i := 0; i < length; i++ {
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fmt.Printf(" data[%d] = %d\n", i, data[i])
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if i >= 2 {
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break
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}
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}
|
||
|
||
// 技巧2: 使用 range 遍历
|
||
fmt.Printf(" 技巧2 - 使用 range 遍历 (更简洁):\n")
|
||
for i, value := range data {
|
||
fmt.Printf(" data[%d] = %d\n", i, value)
|
||
if i >= 2 {
|
||
break
|
||
}
|
||
}
|
||
|
||
// 技巧3: 提前退出
|
||
fmt.Printf(" 技巧3 - 提前退出优化:\n")
|
||
numbers := []int{2, 4, 6, 7, 8, 10, 12}
|
||
|
||
// 查找第一个奇数
|
||
for i, num := range numbers {
|
||
fmt.Printf(" 检查 numbers[%d] = %d", i, num)
|
||
if num%2 == 1 {
|
||
fmt.Printf(" - 找到第一个奇数: %d\n", num)
|
||
break // 找到后立即退出，不继续遍历
|
||
}
|
||
fmt.Printf(" - 偶数，继续查找\n")
|
||
}
|
||
|
||
// 技巧4: 批量处理
|
||
fmt.Printf(" 技巧4 - 批量处理:\n")
|
||
largeData := make([]int, 20)
|
||
for i := range largeData {
|
||
largeData[i] = i + 1
|
||
}
|
||
|
||
batchSize := 5
|
||
fmt.Printf(" 批量处理数据 (批次大小: %d):\n", batchSize)
|
||
|
||
for i := 0; i < len(largeData); i += batchSize {
|
||
end := i + batchSize
|
||
if end > len(largeData) {
|
||
end = len(largeData)
|
||
}
|
||
|
||
batch := largeData[i:end]
|
||
fmt.Printf(" 处理批次 %d-%d: %v\n", i, end-1, batch)
|
||
|
||
// 模拟批量处理
|
||
batchSum := 0
|
||
for _, value := range batch {
|
||
batchSum += value
|
||
}
|
||
fmt.Printf(" 批次总和: %d\n", batchSum)
|
||
}
|
||
|
||
// 技巧5: 避免不必要的操作
|
||
fmt.Printf(" 技巧5 - 避免不必要的操作:\n")
|
||
matrix2 := [][]int{
|
||
{1, 2, 3, 4},
|
||
{5, 6, 7, 8},
|
||
{9, 10, 11, 12},
|
||
}
|
||
|
||
// 只处理对角线元素
|
||
fmt.Printf(" 只处理矩阵对角线元素:\n")
|
||
for i := 0; i < len(matrix2) && i < len(matrix2[0]); i++ {
|
||
fmt.Printf(" 对角线元素 [%d][%d] = %d\n", i, i, matrix2[i][i])
|
||
}
|
||
|
||
fmt.Println()
|
||
}
|
||
|
||
// 辅助函数
|
||
func validateEmail(email string) bool {
|
||
// 简单的邮箱验证（实际应用中应该使用正则表达式）
|
||
if len(email) < 5 {
|
||
return false
|
||
}
|
||
|
||
hasAt := false
|
||
hasDot := false
|
||
atPos := -1
|
||
|
||
for i, char := range email {
|
||
if char == '@' {
|
||
if hasAt || i == 0 || i == len(email)-1 {
|
||
return false
|
||
}
|
||
hasAt = true
|
||
atPos = i
|
||
} else if char == '.' && hasAt && i > atPos+1 && i < len(email)-1 {
|
||
hasDot = true
|
||
}
|
||
}
|
||
|
||
return hasAt && hasDot
|
||
}
|
||
|
||
/*
|
||
运行这个程序：
|
||
go run 03-for-loops.go
|
||
|
||
学习要点：
|
||
1. Go 只有 for 循环，没有 while 和 do-while
|
||
2. for 循环有三种形式：传统形式、while 形式、无限循环形式
|
||
3. break 用于跳出循环，continue 用于跳过当前迭代
|
||
4. 标签可以用来控制嵌套循环的跳转
|
||
5. range 关键字提供了遍历数组、切片、字符串等的便捷方式
|
||
|
||
for 循环的三种形式：
|
||
1. for init; condition; post { ... } // 传统形式
|
||
2. for condition { ... } // while 形式
|
||
3. for { ... } // 无限循环
|
||
|
||
循环控制：
|
||
1. break: 跳出当前循环
|
||
2. continue: 跳过当前迭代，继续下一次迭代
|
||
3. 标签: 可以跳出或跳过指定的外层循环
|
||
|
||
优化建议：
|
||
1. 减少循环内的重复计算
|
||
2. 使用 range 遍历集合类型
|
||
3. 适当使用 break 提前退出
|
||
4. 考虑批量处理大量数据
|
||
5. 避免不必要的嵌套循环
|
||
|
||
常见应用场景：
|
||
1. 数组/切片遍历和处理
|
||
2. 数值计算（累加、阶乘等）
|
||
3. 字符串处理
|
||
4. 数据验证和过滤
|
||
5. 算法实现
|
||
6. 游戏循环
|
||
7. 服务器主循环
|
||
|
||
注意事项：
|
||
1. 避免无限循环（除非有明确的退出条件）
|
||
2. 注意循环变量的作用域
|
||
3. 在嵌套循环中正确使用标签
|
||
4. 考虑循环的时间复杂度
|
||
5. 合理使用 break 和 continue
|
||
*/ |