From 2fbd044016c85e770477b6292a2902caf5ef5a01 Mon Sep 17 00:00:00 2001 From: Unknwon Date: Fri, 17 Jul 2015 02:23:41 +0800 Subject: [PATCH] =?UTF-8?q?=E7=B2=BE=E6=A0=A1=EF=BC=9A5.4?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- eBook/05.4.md | 152 ++++++++++++++++++++++++-------------------------- 1 file changed, 73 insertions(+), 79 deletions(-) diff --git a/eBook/05.4.md b/eBook/05.4.md index 601377e..860f5ce 100644 --- a/eBook/05.4.md +++ b/eBook/05.4.md @@ -10,9 +10,9 @@ for 初始化语句; 条件语句; 修饰语句 {} -Listing 5.6 [for1.go](examples/chapter_5/for1.go)： +示例 5.6 [for1.go](examples/chapter_5/for1.go)： -``` +```go package main import "fmt" @@ -26,13 +26,11 @@ func main() { 输出： -``` -This is the 0 iteration -This is the 1 iteration -This is the 2 iteration -This is the 3 iteration -This is the 4 iteration -``` + This is the 0 iteration + This is the 1 iteration + This is the 2 iteration + This is the 3 iteration + This is the 4 iteration 由花括号括起来的代码块会被重复执行已知次数，该次数是根据计数器（此例为 i）决定的。循环开始前，会执行且仅会执行一次初始化语句 `i := 0;`；这比在循环之前声明更为简短。紧接着的是条件语句 `i < 5;`，在每次循环开始前都会进行判断，一旦判断结果为 false，则退出循环体。最后一部分为修饰语句 `i++`，一般用于增加或减少计数器。 @@ -44,13 +42,15 @@ This is the 4 iteration 您还可以在循环中同时使用多个计数器： - for i, j := 0, N; i < j; i, j = i+1, j-1 {} +```go +for i, j := 0, N; i < j; i, j = i+1, j-1 {} +``` 这得益于 Go 语言具有的平行赋值的特性（可以查看第 7 章 string_reverse.go 中反转数组的示例）。 您可以将两个 for 循环嵌套起来： -``` +```go for i:=0; i<5; i++ { for j:=0; j<10; j++ { println(j) @@ -60,9 +60,9 @@ for i:=0; i<5; i++ { 如果您使用 for 循环迭代一个 Unicode 编码的字符串，会发生什么？ -Listing 5.7 [for_string.go](examples/chapter_5/for_string.go)： +示例 5.7 [for_string.go](examples/chapter_5/for_string.go)： -``` +```go package main import "fmt" @@ -83,46 +83,44 @@ func main() { 输出： -``` -The length of str is: 27 -Character on position 0 is: G -Character on position 1 is: o -Character on position 2 is: -Character on position 3 is: i -Character on position 4 is: s -Character on position 5 is: -Character on position 6 is: a -Character on position 7 is: -Character on position 8 is: b -Character on position 9 is: e -Character on position 10 is: a -Character on position 11 is: u -Character on position 12 is: t -Character on position 13 is: i -Character on position 14 is: f -Character on position 15 is: u -Character on position 16 is: l -Character on position 17 is: -Character on position 18 is: l -Character on position 19 is: a -Character on position 20 is: n -Character on position 21 is: g -Character on position 22 is: u -Character on position 23 is: a -Character on position 24 is: g -Character on position 25 is: e -Character on position 26 is: ! -The length of str2 is: 9 -Character on position 0 is: æ -Character on position 1 is: — -Character on position 2 is: ¥ -Character on position 3 is: æ -Character on position 4 is: œ -Character on position 5 is: ¬ -Character on position 6 is: è -Character on position 7 is: ª -Character on position 8 is: ž -``` + The length of str is: 27 + Character on position 0 is: G + Character on position 1 is: o + Character on position 2 is: + Character on position 3 is: i + Character on position 4 is: s + Character on position 5 is: + Character on position 6 is: a + Character on position 7 is: + Character on position 8 is: b + Character on position 9 is: e + Character on position 10 is: a + Character on position 11 is: u + Character on position 12 is: t + Character on position 13 is: i + Character on position 14 is: f + Character on position 15 is: u + Character on position 16 is: l + Character on position 17 is: + Character on position 18 is: l + Character on position 19 is: a + Character on position 20 is: n + Character on position 21 is: g + Character on position 22 is: u + Character on position 23 is: a + Character on position 24 is: g + Character on position 25 is: e + Character on position 26 is: ! + The length of str2 is: 9 + Character on position 0 is: æ + Character on position 1 is: — + Character on position 2 is: ¥ + Character on position 3 is: æ + Character on position 4 is: œ + Character on position 5 is: ¬ + Character on position 6 is: è + Character on position 7 is: ª + Character on position 8 is: ž 如果我们打印 str 和 str2 的长度，会分别得到 27 和 9。 @@ -139,14 +137,12 @@ Character on position 8 is: ž 创建一个程序，要求能够打印类似下面的结果（直到每行 25 个字符时为止）： -``` -G -GG -GGG -GGGG -GGGGG -GGGGGG -``` + G + GG + GGG + GGGG + GGGGG + GGGGGG 1. 使用 2 层嵌套 for 循环。 2. 使用一层 for 循环以及字符串截断。 @@ -171,7 +167,7 @@ for 结构的第二种形式是没有头部的条件判断迭代（类似其它 Listing 5.8 [for2.go](examples/chapter_5/for2.go)： -``` +```go package main import "fmt" @@ -188,14 +184,12 @@ func main() { 输出： -``` -The variable i is now: 4 -The variable i is now: 3 -The variable i is now: 2 -The variable i is now: 1 -The variable i is now: 0 -The variable i is now: -1 -``` + The variable i is now: 4 + The variable i is now: 3 + The variable i is now: 2 + The variable i is now: 1 + The variable i is now: 0 + The variable i is now: -1 ## 5.4.3 无限循环 @@ -209,7 +203,7 @@ The variable i is now: -1 无限循环的经典应用是服务器，用于不断等待和接受新的请求。 -``` +```go for t, err = p.Token(); err == nil; t, err = p.Token() { ... } @@ -221,7 +215,7 @@ for t, err = p.Token(); err == nil; t, err = p.Token() { 要注意的是，`val` 始终为集合中对应索引的值拷贝，因此它一般只具有只读性质，对它所做的任何修改都不会影响到集合中原有的值（**译者注：如果 `val` 为指针，则会产生指针的拷贝，依旧可以修改集合中的原值**）。一个字符串是 Unicode 编码的字符（或称之为 `rune`）集合，因此您也可以用它迭代字符串： -``` +```go for pos, char := range str { ... } @@ -229,9 +223,9 @@ for pos, char := range str { 每个 rune 字符和索引在 for-range 循环中是一一对应的。它能够自动根据 UTF-8 规则识别 Unicode 编码的字符。 -Listing 5.9 [range_string.go](examples/chapter_5/range_string.go)： +示例 5.9 [range_string.go](examples/chapter_5/range_string.go)： -``` +```go package main import "fmt" @@ -323,7 +317,7 @@ index int(rune) rune char bytes **练习 5.9** 以下程序的输出结果是什么？ -``` +```go for i := 0; i < 5; i++ { var v int fmt.Printf("%d ", v) @@ -335,7 +329,7 @@ for i := 0; i < 5; i++ { 1. -``` +```go for i := 0; ; i++ { fmt.Println("Value of i is now:", i) } @@ -343,7 +337,7 @@ for i := 0; ; i++ { 2. -``` +```go for i := 0; i < 3; { fmt.Println("Value of i:", i) } @@ -351,7 +345,7 @@ for i := 0; i < 3; { 3. -``` +```go s := "" for ; s != "aaaaa"; { fmt.Println("Value of s:", s) @@ -361,7 +355,7 @@ for ; s != "aaaaa"; { 4. -``` +```go for i, j, s := 0, 5, "a"; i < 3 && j < 100 && s != "aaaaa"; i, j, s = i+1, j+1, s + "a" { fmt.Println("Value of i, j, s:", i, j, s)