diff --git a/code/2/2.1.nullptr.cpp b/code/2/2.01.nullptr.cpp
similarity index 100%
rename from code/2/2.1.nullptr.cpp
rename to code/2/2.01.nullptr.cpp
diff --git a/code/2/2.2.constexpr.cpp b/code/2/2.02.constexpr.cpp
similarity index 100%
rename from code/2/2.2.constexpr.cpp
rename to code/2/2.02.constexpr.cpp
diff --git a/code/2/2.3.if.switch.cpp b/code/2/2.03.if.switch.cpp
similarity index 100%
rename from code/2/2.3.if.switch.cpp
rename to code/2/2.03.if.switch.cpp
diff --git a/code/2/2.4.initializer.list.cpp b/code/2/2.04.initializer.list.cpp
similarity index 100%
rename from code/2/2.4.initializer.list.cpp
rename to code/2/2.04.initializer.list.cpp
diff --git a/code/2/2.5.structured.binding.cpp b/code/2/2.05.structured.binding.cpp
similarity index 100%
rename from code/2/2.5.structured.binding.cpp
rename to code/2/2.05.structured.binding.cpp
diff --git a/code/2/2.6.auto.cpp b/code/2/2.06.auto.cpp
similarity index 100%
rename from code/2/2.6.auto.cpp
rename to code/2/2.06.auto.cpp
diff --git a/code/2/2.7.decltype.cpp b/code/2/2.07.decltype.cpp
similarity index 100%
rename from code/2/2.7.decltype.cpp
rename to code/2/2.07.decltype.cpp
diff --git a/code/2/2.8.tail.return.type.cpp b/code/2/2.08.tail.return.type.cpp
similarity index 100%
rename from code/2/2.8.tail.return.type.cpp
rename to code/2/2.08.tail.return.type.cpp
diff --git a/code/2/2.9.decltype.auto.cpp b/code/2/2.09.decltype.auto.cpp
similarity index 100%
rename from code/2/2.9.decltype.auto.cpp
rename to code/2/2.09.decltype.auto.cpp
diff --git a/code/2/2.4.cpp b/code/2/2.4.cpp
deleted file mode 100644
index c9cd59d..0000000
--- a/code/2/2.4.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-//
-// 2.4.cpp
-// c++1x tutorial
-//
-// created by changkun at changkun.de
-//
-// 区间迭代
-
-#include <iostream>
-#include <vector>
-
-int main() {
-    int array[] = {1,2,3,4,5};
-    for(auto &x : array) {
-        std::cout << x << std::endl;
-    }
-
-    // 传统 C++ 写法
-    std::vector<int> arr(5, 100);
-    for(std::vector<int>::iterator i = arr.begin(); i != arr.end(); ++i) {
-        std::cout << *i << std::endl;
-    }
-    
-    // C++11 写法
-    // & 启用了引用, 如果没有则对 arr 中的元素只能读取不能修改
-    for(auto &i : arr) {
-        std::cout << i << std::endl;
-    }
-    return 0;
-}
diff --git a/code/2/todo/2.6.autox.cpp b/code/2/todo/2.6.autox.cpp
deleted file mode 100644
index e87c8fe..0000000
--- a/code/2/todo/2.6.autox.cpp
+++ /dev/null
@@ -1,49 +0,0 @@
-//
-// 2.3.cpp
-// c++1x tutorial
-//
-// created by changkun at changkun.de
-//
-// auto/decltype/尾返回类型/返回类型推导
-
-
-#include <iostream>
-
-// 传统 C++
-template <typename R, typename T, typename U>
-R add1(T x, U y) {
-    return x+y;
-}
-
-// 尾返回类型
-template <typename T, typename U>
-auto add2(T x, U y) -> decltype(x+y) {
-    return x+y;
-}
-
-// C++14 返回类型推导
-template <typename T, typename U>
-auto add3(T x, U y) {
-    return x+y;
-}
-
-int main() {
-    auto i = 5;
-    
-    int arr[10] = {0};
-    auto auto_arr = arr;        // 正确，对整个类型进行推导
-    // auto auto_arr2[10] = arr;   // 错误,  无法推导数组元素类型
-
-    auto x = 1;
-    auto y = 2;
-    decltype(x+y) z1;
-    //auto z2;                  // 错误, 无法推导
-
-    
-    std::cout << add1<int, int, int>(1,1) << std::endl;
-    std::cout << add1<int, int>(1,1) << std::endl;
-    std::cout << add1<int, int>(1,1) << std::endl;
-    
-    
-    return 0;
-}
diff --git a/code/2/2.6.cpp b/code/2/todo/2.6.cpp
similarity index 100%
rename from code/2/2.6.cpp
rename to code/2/todo/2.6.cpp