diff --git a/.vscode/settings.json b/.vscode/settings.json
index 230b7cf9..73603a7f 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,4 +1,5 @@
 {
+    "editor.formatOnSave": true,
     "files.associations": {
         "vector": "cpp",
         "iosfwd": "cpp",
diff --git a/ch06/README.md b/ch06/README.md
index 5ad4727c..2919c007 100644
--- a/ch06/README.md
+++ b/ch06/README.md
@@ -223,7 +223,7 @@ Error (Clang):
 
 ## Exercise 6.31
 
-when you can find the preexited object that the reference refered.
+when you can find the preexisted object that the reference refered.
 
 ## Exercise 6.32
 
diff --git a/ch06/ex6_04.cpp b/ch06/ex6_04.cpp
index 0582ff6f..36c5066e 100644
--- a/ch06/ex6_04.cpp
+++ b/ch06/ex6_04.cpp
@@ -1,36 +1,31 @@
-/*
-=================================================================================
-C++ Primer 5th Exercise Answer Source Code
-Copyright (C) 2014-2015 github.com/pezy/CppPrimer
+// Write a function that interacts with the user, asking for a number and
+// generating the factorial of that number. Call this function from main.
 
-Write a function that interacts with the user, asking for a number and
-generating the factorial of that number. Call this function from main.
-
-About the magic number(13): https://github.com/Mooophy/Cpp-Primer/pull/172
-
-If you have questions, try to connect with me: pezy<pezy.dev@gmail.com>
-=================================================================================
-*/
+// About the magic number(13): https://github.com/Mooophy/Cpp-Primer/pull/172
 
 #include <iostream>
 #include <string>
 
+using std::cin;
+using std::cout;
+using std::endl;
+
 int fact(int val)
 {
-	int ret = 1;
-	while (val > 1)
-		ret *= val--;
-	return ret;
+    int ret = 1;
+    while (val > 1) ret *= val--;
+    return ret;
 }
 
-void factorial_with_interacts() {
-	for (int val = 0; std::cout << "Enter a number within [0, 13): ", std::cin >> val; ) {
-		if (val < 0 || val > 12) continue;
-		std::cout << val << "! =" << fact(val) << std::endl;
-	}
+void factorial_with_interacts()
+{
+    for (int val = 0; cout << "Enter a number within [0, 13): ", cin >> val;) {
+        if (val < 0 || val > 12) continue;
+        cout << val << "! =" << fact(val) << endl;
+    }
 }
 
 int main()
 {
-	factorial_with_interacts();
+    factorial_with_interacts();
 }
\ No newline at end of file
diff --git a/ch06/ex6_10.cpp b/ch06/ex6_10.cpp
index 251fa407..4a92680d 100644
--- a/ch06/ex6_10.cpp
+++ b/ch06/ex6_10.cpp
@@ -1,28 +1,25 @@
-//!@Yue wang
-//!
-//! Exercise 6.10:
-//! Using pointers, write a function to swap the values of two ints.
-//! Test the function by calling it and printing the swapped values.
-//!
+// Using pointers, write a function to swap the values of two ints.
+// Test the function by calling it and printing the swapped values.
+
 #include <iostream>
-#include <string>
 #include <stdexcept>
+#include <string>
 
-void swap(int* lhs, int* rhs)
+using std::cin;
+using std::cout;
+using std::endl;
+
+void swap(int* const lhs, int* const rhs)
 {
-    int tmp;
-    tmp = *lhs;
+    auto tmp = *lhs;
     *lhs = *rhs;
     *rhs = tmp;
 }
 
 int main()
 {
-    for (int lft, rht;
-         std::cout << "Please Enter:\n", std::cin >> lft >> rht;) {
-        swap(&lft, &rht);
-        std::cout << lft << " " << rht << std::endl;
+    for (int lht, rht; cout << "Please Enter:\n", cin >> lht >> rht;) {
+        swap(&lht, &rht);
+        cout << lht << " " << rht << endl;
     }
-
-    return 0;
 }
diff --git a/ch06/ex6_11.cpp b/ch06/ex6_11.cpp
index 0e20bd9d..2694d0fa 100644
--- a/ch06/ex6_11.cpp
+++ b/ch06/ex6_11.cpp
@@ -10,5 +10,4 @@ int main()
     int i = 42;
     reset(i);
     std::cout << i << std::endl;
-    return 0;
 }
diff --git a/ch06/ex6_12.cpp b/ch06/ex6_12.cpp
index d442f86f..1484ba2e 100644
--- a/ch06/ex6_12.cpp
+++ b/ch06/ex6_12.cpp
@@ -1,28 +1,26 @@
-//!@Yue Wang
-//!
-//! Exercise 6.12:
-//! Rewrite the program from exercise 6.10 in § 6.2.1 (p. 210) to use
-//! references instead of pointers to swap the value of two ints. Which
-//! version do you think would be easier to use and why?
-//  The version using reference is easier.
-//!
+// Rewrite the program from exercise 6.10 in 6.2.1 (p. 210) to use
+// references instead of pointers to swap the value of two ints. Which
+// version do you think would be easier to use and why?
+// The version using reference is easier.
+
 #include <iostream>
 #include <string>
 
+using std::cin;
+using std::cout;
+using std::endl;
+
 void swap(int& lhs, int& rhs)
 {
-    int temp = lhs;
+    auto tmp = lhs;
     lhs = rhs;
-    rhs = temp;
+    rhs = tmp;
 }
 
 int main()
 {
-    for (int left, right;
-         std::cout << "Please Enter:\n", std::cin >> left >> right;) {
+    for (int left, right; cout << "Please Enter:\n", cin >> left >> right;) {
         swap(left, right);
-        std::cout << left << " " << right << std::endl;
+        cout << left << " " << right << endl;
     }
-
-    return 0;
 }
diff --git a/ch06/ex6_21.cpp b/ch06/ex6_21.cpp
index 5be53b5e..883d98fb 100644
--- a/ch06/ex6_21.cpp
+++ b/ch06/ex6_21.cpp
@@ -1,15 +1,10 @@
-//! @Alan
-//!
-//! Exercise 6.21:
-//! Write a function that takes an int and a pointer to an int and
-//! returns the larger of the int value or the value to which the
-//! pointer points. What type should you use for the pointer?
-//!
+// Write a function that takes an int and a pointer to an int and
+// returns the larger of the int value or the value to which the
+// pointer points. What type should you use for the pointer?
 
 #include <iostream>
-using std::cout;
 
-int LargerOne(const int i, const int* ip)
+int LargerOne(int i, const int* const ip)
 {
     return (i > *ip) ? i : *ip;
 }
@@ -17,7 +12,5 @@ int LargerOne(const int i, const int* ip)
 int main()
 {
     int c = 6;
-    cout << LargerOne(7, &c);
-
-    return 0;
+    std::cout << LargerOne(7, &c) << std::endl;
 }
diff --git a/ch06/ex6_22.cpp b/ch06/ex6_22.cpp
index 91bfdd9e..9779c9df 100644
--- a/ch06/ex6_22.cpp
+++ b/ch06/ex6_22.cpp
@@ -1,24 +1,19 @@
-//! @Yue Wang
-//!
-//! Exercise 6.22:
-//! Write a function to swap two int pointers.
-//!
+// Write a function to swap two int pointers.
+
 #include <iostream>
 
-void swap(int*& lft, int*& rht)
+void swap(const int*& lhs, const int*& rhs)
 {
-    auto tmp = lft;
-    lft = rht;
-    rht = tmp;
+    auto temp = lhs;
+    lhs = rhs;
+    rhs = temp;
 }
 
 int main()
 {
-    int i = 42, j = 99;
-    auto lft = &i;
-    auto rht = &j;
-    swap(lft, rht);
-    std::cout << *lft << " " << *rht << std::endl;
-
-    return 0;
+    const int i = 42, j = 99;
+    auto lhs = &i;
+    auto rhs = &j;
+    swap(lhs, rhs);
+    std::cout << *lhs << " " << *rhs << std::endl;
 }
diff --git a/ch06/ex6_23.cpp b/ch06/ex6_23.cpp
index bf2c6b83..04205616 100644
--- a/ch06/ex6_23.cpp
+++ b/ch06/ex6_23.cpp
@@ -1,11 +1,16 @@
+// Write your own versions of each of the print functions
+// presented in this section. Call each of these functions to print i and j
+// defined as follows:
+// int i = 0, j[2] = {0, 1};
+
 #include <iostream>
 
-using std::cout;
-using std::endl;
 using std::begin;
+using std::cout;
 using std::end;
+using std::endl;
 
-void print(int* pi)
+void print(int* const pi)
 {
     if (pi) cout << *pi << endl;
 }
@@ -19,19 +24,20 @@ void print(const char* p)
 
 void print(const int* beg, const int* end)
 {
-    while (beg != end) cout << *beg++ << endl;
+    while (beg != end) cout << *beg++ << " ";
+    cout << endl;
 }
 
 void print(const int ia[], size_t size)
 {
-    for (size_t i = 0; i != size; ++i) {
-        cout << ia[i] << endl;
-    }
+    for (size_t i = 0; i != size; ++i) cout << ia[i] << " ";
+    cout << endl;
 }
 
-void print(const int(&arr)[2])
+void print(const int (&arr)[2])
 {
-    for (auto i : arr) cout << i << endl;
+    for (auto i : arr) cout << i << " ";
+    cout << endl;
 }
 
 int main()
diff --git a/ch06/ex6_25_26.cpp b/ch06/ex6_25_26.cpp
index 77917f27..dc8ae6eb 100644
--- a/ch06/ex6_25_26.cpp
+++ b/ch06/ex6_25_26.cpp
@@ -1,11 +1,8 @@
-//! @Yue Wang
-//!
-//! Exercise 6.25: Write a main function that takes two arguments.
-//! Concatenate the supplied arguments and print the resulting string.
-//!
-//! Exercise 6.26: Write a program that accepts the options presented
-//! in this section. Print the values of the arguments passed to main.
-//!
+// Write a main function that takes two arguments.
+// Concatenate the supplied arguments and print the resulting string.
+
+// Write a program that accepts the options presented
+// in this section. Print the values of the arguments passed to main.
 
 #include <iostream>
 #include <string>
@@ -19,5 +16,4 @@ int main(int argc, char** argv)
     }
 
     std::cout << str << std::endl;
-    return 0;
 }
diff --git a/ch06/ex6_27.cpp b/ch06/ex6_27.cpp
index 4823eb6a..7041a9b0 100644
--- a/ch06/ex6_27.cpp
+++ b/ch06/ex6_27.cpp
@@ -1,7 +1,7 @@
-#include <iostream>
 #include <initializer_list>
+#include <iostream>
 
-int sum(std::initializer_list<int> il)
+int sum(const std::initializer_list<int>& il)
 {
     int sum = 0;
     for (auto i : il) sum += i;
@@ -11,5 +11,4 @@ int sum(std::initializer_list<int> il)
 int main(void)
 {
     std::cout << sum({1, 2, 3, 4, 5}) << std::endl;
-    return 0;
 }
diff --git a/ch06/ex6_33.cpp b/ch06/ex6_33.cpp
index 60b4a8c7..230d854a 100644
--- a/ch06/ex6_33.cpp
+++ b/ch06/ex6_33.cpp
@@ -1,8 +1,10 @@
+// Write a recursive function to print the contents of a vector
+
 #include <iostream>
 #include <vector>
 
-using std::vector;
 using std::cout;
+using std::vector;
 using Iter = vector<int>::iterator;
 
 void print(Iter beg, Iter end)
@@ -17,5 +19,4 @@ int main()
 {
     vector<int> vec{1, 2, 3, 4, 5, 6, 7, 8, 9};
     print(vec.begin(), vec.end());
-    return 0;
 }
diff --git a/ch06/ex6_42.cpp b/ch06/ex6_42.cpp
index 50f8c6ba..bbd917f0 100644
--- a/ch06/ex6_42.cpp
+++ b/ch06/ex6_42.cpp
@@ -1,20 +1,13 @@
-//! @creator by Wang Yue
-//! @refactor by pezy
-//!
-//! @date 27, July. 2015
-//!
-//! @question
-//! Give the second parameter of make_plural (§ 6.3.2, p. 224) a default
-//! argument of 's'. Test your program by printing singular and plural versions
-//! of the words success and failure.
-//!
+// Give the second parameter of make_plural (6.3.2, p. 224) a default
+// argument of 's'. Test your program by printing singular and plural versions
+// of the words success and failure.
 
 #include <iostream>
 #include <string>
 
-using std::string;
 using std::cout;
 using std::endl;
+using std::string;
 
 string make_plural(size_t ctr, const string& word, const string& ending = "s")
 {
@@ -27,6 +20,4 @@ int main()
          << make_plural(1, "failure") << endl;
     cout << "plural : " << make_plural(2, "success", "es") << " "
          << make_plural(2, "failure") << endl;
-
-    return 0;
 }
diff --git a/ch06/ex6_44.cpp b/ch06/ex6_44.cpp
index 8dfec775..06e21c17 100644
--- a/ch06/ex6_44.cpp
+++ b/ch06/ex6_44.cpp
@@ -1,8 +1,4 @@
-//! @Alan
-//!
-//! Exercise 6.44: Rewrite the isShorter function from § 6.2.2 (p. 211) to be
-//! inline.
-//!
+// Rewrite the isShorter function from 6.2.2 (p. 211) to be inline.
 
 #include <iostream>
 #include <string>
diff --git a/ch06/ex6_47.cpp b/ch06/ex6_47.cpp
index 97f25a21..e7627c58 100644
--- a/ch06/ex6_47.cpp
+++ b/ch06/ex6_47.cpp
@@ -1,16 +1,14 @@
-//
-//  main.cpp
-//  Test
-//
-//  Created by pezy on 14/10/30.
-//  Copyright (c) 2014 pezy. All rights reserved.
-//
+// Revise the program you wrote in the exercises in 6.3.2 (p.
+// 228) that used recursion to print the contents of a vector to conditionally
+// print information about its execution. For example, you might print the size
+// of the vector on each call. Compile and run the program with debugging turned
+// on and again with it turned off.
 
 #include <iostream>
 #include <vector>
-using std::vector;
 using std::cout;
 using std::endl;
+using std::vector;
 
 //#define NDEBUG
 
@@ -32,6 +30,4 @@ int main()
     vector<int> vec{1, 2, 3, 4, 5, 6, 7, 8, 9};
     printVec(vec);
     cout << endl;
-
-    return 0;
 }
diff --git a/ch06/ex6_51.cpp b/ch06/ex6_51.cpp
index f238c6c1..efb14da1 100644
--- a/ch06/ex6_51.cpp
+++ b/ch06/ex6_51.cpp
@@ -1,3 +1,8 @@
+// Write all four versions of f. Each function should print a
+// distinguishing message. Check your answers for the previous exercise. If your
+// answers were incorrect, study this section until you understand why your
+// answers were wrong.
+
 #include <iostream>
 using std::cout;
 using std::endl;
@@ -24,10 +29,8 @@ void f(double, double)
 
 int main()
 {
-    f(2.56, 42); // error: 'f' is ambiguous.
+    // f(2.56, 42); // error: 'f' is ambiguous.
     f(42);
     f(42, 0);
     f(2.56, 3.14);
-
-    return 0;
 }
diff --git a/ch06/ex6_54_55_56.cpp b/ch06/ex6_54_55_56.cpp
index 0cc022e2..39293e17 100644
--- a/ch06/ex6_54_55_56.cpp
+++ b/ch06/ex6_54_55_56.cpp
@@ -1,5 +1,3 @@
-//! @Yue Wang
-//!
 //! Exercise 6.54:
 //! Write a declaration for a function that takes two int
 //! parameters and returns an int, and declare a vector whose
@@ -17,8 +15,8 @@
 #include <iostream>
 #include <string>
 #include <vector>
-using std::vector;
 using std::cout;
+using std::vector;
 
 //!
 //! @brief Exercise 6.54