add changes to ch12_1

ch12/1/ch12_1.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+)
+
+func PrintNumbers() {
+	const IN_CHAN_NUM = 2
+	numCh := make(chan int, 20)
+	completeCh := make(chan int)
+	defer close(numCh)
+	defer close(completeCh)
+	for i := 0; i < IN_CHAN_NUM; i++ {
+		go func() {
+			for j := 0; j < 10; j++ {
+				numCh <- (rand.Int() % 100)
+			}
+		}()
+	}
+	go func() {
+		i := 0
+		for num := range numCh {
+			fmt.Println(num)
+			i++
+			if i == 20 {
+				break
+			}
+		}
+		completeCh <- 1
+	}()
+	select {
+	case <-completeCh:
+	}
+}
+
+func main() {
+	PrintNumbers()
+}