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select中case的使用

请问以下程序的输出结果？

func case1() {c1 := make(chan int)c2 := make(chan int)close(c1)close(c2)select {case <-c1:fmt.Println("c1")case c2 <- 1:fmt.Println("c2")default:fmt.Println("default")}
}

非阻塞select

以下程序输出结果？

func case2() {c := make(chan int, 1)done := falsefor !done {select {case <-c:print(1)c = nilcase c <- 1:print(2)default:print(3)done = true}}
}

有4个goroutine，按编号1、2、3、4循环打印

func case3() {ch := make([]chan int, 4)for i := range ch {ch[i] = make(chan int)go func(i int) {for {v := <-ch[i]fmt.Println(v + 1)time.Sleep(time.Second)ch[(i+1)%4] <- (v + 1) % 4}}(i)}ch[0] <- 0select {}
}

使用三个协程，每秒钟打印cat dog fish

func case4() {chCat := make(chan struct{})chDog := make(chan struct{})chFish := make(chan struct{})go func() {for {<-chCatfmt.Println("cat")time.Sleep(time.Second)chDog <- struct{}{}}}()go func() {for {<-chDogfmt.Println("dog")time.Sleep(time.Second)chFish <- struct{}{}}}()go func() {for {<-chFishfmt.Println("fish")time.Sleep(time.Second)chCat <- struct{}{}}}()chCat <- struct{}{}select {}
}

实现两个goroutine轮流输出A 1 B 2 C 3…Z 26

func case5() {byteCh := make(chan struct{}, 1)intCh := make(chan struct{}, 1)byteCh <- struct{}{}go func() {for {for i := 'A' - 0; i <= 'Z'-0; i++ {<-byteChfmt.Println(string(i))intCh <- struct{}{}}}//return}()go func() {for {for i := 1; i <= 26; i++ {<-intChfmt.Println(i)byteCh <- struct{}{}}}//return}()time.Sleep(time.Second)
}

用N个goroutine去按顺序打印数字

func case6() {const n = 5ch := make([]chan int, n)for i := 0; i < n; i++ {ch[i] = make(chan int, 1)}for i := 0; i < n; i++ {go printNum(i, ch[i])}count := 0for i := 0; i < 100; i++ {for j := 0; j < n; j++ {ch[j] <- countcount++time.Sleep(time.Second * 1)}}
}func printNum(gid int, ch chan int) {for {fmt.Printf("g:%d，num:%d\n", gid, <-ch)}
}

有一个数组，用两个协程，一个打印所有偶数的和，一个打印所有奇数的和，要用for channel机制

func case7() {nums := [5]int{1, 2, 32, 41, 5}oneCh := make(chan int, 1)twoCh := make(chan int, 1)go printOld(oneCh, nums[:])go printNew(twoCh, nums[:])fmt.Println(<-oneCh)fmt.Println(<-twoCh)
}func printOld(ch chan int, arr []int) {sum := 0for _, v := range arr {if v%2 == 0 {sum += v}}ch <- sum
}func printNew(ch chan int, arr []int) {sum := 0for _, v := range arr {if v%2 != 0 {sum += v}}ch <- sum
}