update lesson2

Author: jincheng9

workspace/lesson2/array.go

@@ -0,0 +1,9 @@
+package main
+
+import "fmt"
+
+func main() {
+    a := [5]int{}
+    a[0] = 1
+    fmt.Println(a)
+}

workspace/lesson2/readme.md

@@ -19,6 +19,47 @@
         }
         ```
 
+    * **注意**：string是immutable的，不能在初始化string变量后，修改string里的值，除非对string变量重新赋值
+
+        ```go
+        package main
+        
+        import "fmt"
+        
+        func main() {
+            str := "abc"
+            str = "def" // ok
+            /* 下面的就不行，编译报错：cannot assign to str[0] (strings are immutable)
+            str[0] = "d"
+            */
+            fmt.Println(str)
+        }
+        ```
+
+    * 字符串里字符的访问可以通过str[index]下标索引或者range迭代的方式进行访问
+
+        ```go
+        package main
+        
+        import "fmt"
+        
+        func main() {
+            str := "abc"
+            /*下标访问*/
+            size := len(str)
+            for i:=0; i<size; i++ {
+                fmt.Printf("%d ", str[i])
+            }
+            fmt.Println()
+            
+            /*range迭代访问*/
+            for _, value := range str {
+                fmt.Printf("%d ", value)
+            }
+            fmt.Println()
+        }
+        ```
+
 
 
 * bool

workspace/lesson2/string.go

@@ -0,0 +1,12 @@
+package main
+
+import "fmt"
+
+func main() {
+    str := "abc"
+    str = "def" // ok
+    /* 下面的就不行，编译报错：cannot assign to str[0] (strings are immutable)
+    str[0] = "d"
+    */
+    fmt.Println(str[0])
+}

workspace/lesson2/string2.go

@@ -0,0 +1,19 @@
+package main
+
+import "fmt"
+
+func main() {
+    str := "abc"
+    /*下标访问*/
+    size := len(str)
+    for i:=0; i<size; i++ {
+        fmt.Printf("%d ", str[i])
+    }
+    fmt.Println()
+    
+    /*range迭代访问*/
+    for _, value := range str {
+        fmt.Printf("%d ", value)
+    }
+    fmt.Println()
+}