update lesson6 and lesson7

Author: jincheng9

workspace/lesson6/switch.go

@@ -32,4 +32,17 @@ func main() {
 		result = "exception"
 	}
 	println("gender:", gender, "result:", result) // the value of result is "better"
+
+
+	switch {
+	case grade >= 90:
+		level = "A"
+	case grade >= 80 && grade < 90:
+		level = "B"
+	case grade >= 60 && grade <80:
+		level = "C"
+	case grade <60:
+		level = "D"
+	}
+	println("grade:", grade, "level:", level)
 }

workspace/lesson7/control-each.go

@@ -0,0 +1,18 @@
+package main
+
+func main() {
+	str := "abcdefg"
+	for index, char := range str {
+		println("index=", index, "char=", char)
+	}
+
+	numbers := [6]int{1, 2, 3, 5} // size为6的数组，第5个和第6个元素的值是默认值0
+	for index, value := range numbers {
+		println("index=", index, "value=", value)
+	}
+
+	strings := []string{"google", "nb"} // 2个元素的字符串数组
+	for index, value := range strings {
+		println("index=", index, "value=", value)
+	}
+}

workspace/lesson7/control.go

@@ -0,0 +1,28 @@
+package main
+
+const num int = 10
+
+func main() {
+	var sum = 0
+	for i:=1; i<=num; i++ {
+		sum +=i
+	}
+
+	var sum2 = 0
+	var j int = 0
+	for j<=10 {
+		sum2 += j
+		j++
+	}
+	println("sum2=", sum2)
+
+	for {
+		println("test infinite loop")
+		break
+	}
+
+	for true {
+		println("test infinite loop2")
+		break
+	}
+}

workspace/lesson7/goto.go

@@ -0,0 +1,21 @@
+package main
+
+import "fmt"
+
+func main() {
+	LOOP: 
+		println("Enter your age:")
+		var age int
+		_, err := fmt.Scan(&age) // 接受控制台输入
+		if err != nil {
+			println("error:", err)
+			goto LOOP
+		}
+		if age < 18 {
+			println("You are not eligible to vote!")
+			goto LOOP
+		} else {
+			println("You are eligible to vote!")
+		}
+		println("all finish")
+}

workspace/lesson7/readme.md

@@ -0,0 +1,88 @@
+# f循环控制
+
+* for的4种用法
+
+  * 用法1: 类似C++的for(int i=0; i<100; i++)
+
+    ```go
+    for init; condition; post {
+      do sth
+    }
+    for ; condition; { // 类似用法2
+      do sth
+    }
+    ```
+
+  * 用法2：类似C++的while循环
+
+    ```go
+    for condition {
+      do sth
+    }
+    ```
+
+  * 用法3: 死循环，类似C++的for(;;)
+
+    ```go
+    for {
+      do sth
+    }
+    ```
+
+  * 用法4: For-each range循环, 类似python的 for k,v in dict.items()
+
+    可以对slice，map，数组和字符串等数据类型进行For-each迭代循环
+
+    ```go
+    for key, value := range map1 { // 遍历map
+      do sth
+    }
+    for index, value := range list { // 遍历数组
+      do sth
+    }
+    for index, character := range str { // 遍历字符串
+      do sth
+    }
+    ```
+
+  * break：跳出for循环或者switch控制逻辑
+
+  * continue：结束当前循环，继续下一轮循环
+
+* goto：类似C++里的goto
+
+  * 语法
+
+  ```go
+  label: statement
+  goto label
+  ```
+
+  * 代码示例
+
+  ```go
+  package main
+  
+  import "fmt"
+  
+  func main() {
+  	LOOP: 
+  		println("Enter your age:")
+  		var age int
+  		_, err := fmt.Scan(&age) // 接受控制台输入
+  		if err != nil {
+  			println("error:", err)
+  			goto LOOP
+  		}
+  		if age < 18 {
+  			println("You are not eligible to vote!")
+  			goto LOOP
+  		} else {
+  			println("You are eligible to vote!")
+  		}
+  		println("all finish")
+  }
+  ```
+
+  
+