Golang Learning Excerpt Two: Control statements

This is a creation in Article, where the information may have evolved or changed.

If statement

i f x > 0 {   // {是强制的,且必须和if在同一行 return y} else { return x}

If and switch accept initialization statements, which are typically used to set a (local) variable.

if err := Chmod(0664); err != nil { //nil 与 C 的 NULL 类似fmt.Printf(err)  //err 的作用域被限定在 if 内return err}

Goto statement

Use Goto to jump to a label that must be defined within the current function

func myfunc() {         i := 0 Here:     // 这行的第一个词,以分号结束作为标签,标签名区分大小写        println(i)        i++        goto Here   // 跳转}

For statement

Go's for Loop has three forms, only one of which uses semicolons.

for init; condition; post { } // 和C的for一样for condition {}              // 和while一样for {}                        // 死循环1、sum := 0for i:=0; i<10; i++ {sum+=i ←sum = sum + i 的简化写法 } 2、for i,j:=0, len(a)-1; i<j; i,j=i+1,j-1 {a[i], a[j] = a[j], a[i] //平行赋值 }

Break and Continue

Use Break to exit the loop prematurely, and break terminates the current loop.

for i:=0; i<10; i++ {   if i>5{      break //终止这个循环,只打印 0 到 5   }   println(i)}

When looping through nested loops, you can specify a label after break. Use a label to determine which loop is terminated:

J: for j:=0; j<5; j++ {    for i:=0; i<10; i++ {       if i>5{           break J // 现在种植的是j循环，而不是i的那个        }        println(i)      } }

Use continue to let the loop go to the next iteration and skip over all the remaining code. The following loop prints 0 to 5.

for i:=0; i<10; i++ {     if i>5{        continue // 跳过循环中所有的代码println(i)    }    println(i)}

Range

Range can be used for loops, and support for slice, array, string, map, and Channel,range are iterators that, when called, return a key-value pair from the contents of the loop. Depending on the content, range returns different things.

// 遍历arraylist := []string {"a", "b", "c", "d", "e", "f"} for k, v := range list {   // k,v键值对：k为key，v为value}// 遍历字符串for pos, char := range "aΦx" {fmt.Printf("character '%c' starts at byte position %d\n",char, pos)}

Switch statement

The switch of Go is very flexible. The expression does not have to be a constant or an integer, and the process is performed from top to bottom until a match is found, and if switch does not have an expression, it matches true. This creates a possibility--using switch to write if-else-if-else judgment sequences.

func unhex(c byte) byte {   switch {    case '0'<=c&&c<='9': return c - '0'    case 'a'<=c&&c<='f': return c - 'a' + 10    case 'A'<=c&&c<='F': return c - 'A' + 10  }  return 0 }

It does not match the failure automatically after the attempt is made, but you can use Fallthrough to make it do so. No Fallthrough:

switch i { case 0:  // 空的case体case 1:             f() // 当i==0时，f不会被调用！}

And this:

switch i {   case 0:  fallthrough  case 1:        f() // 当i==0时，f会被调用！ }

Use default to specify the behavior when all other branches do not match.

switch i {   case 0:   case 1:          f()  default:         g() //当i不等于0或1时调用}

A branch can use a comma-delimited list.

func shouldEscape(c byte) bool {     switch c {      case ' ', '?', '&', '=', '#', '+':    // ,或者 “or”都可以                    return true    }  return false}

Example of using switch to compare byte arrays:

func Compare(a, b []byte) int {    for i:=0; i< len(a)&&i< len(b); i++ {      switch {        case a[i] > b[i]:          return 1        case a[i] < b[i]:          return -1        }    }      switch { 1        case len(a) < len(b):          return -1        case len(a) > len(b):          return 1        }  return 0}