fix the exercise 5.4
Merge pull request #43 from pezy/upstream

Improved : exercise 5.4
Update ex7_23_24_25.cpp
Update ex7_23_24_25.cpp
Update ex7_23_24_25.cpp
Merge pull request #44 from shbling/patch-7

Update ex7_23_24_25.cpp
Update ex7_23_24_25.cpp
Merge pull request #45 from shbling/patch-8

Update ex7_23_24_25.cpp
Update ex7_27.cpp
Update ex7_31.cpp
Merge pull request #48 from shbling/patch-1

Update ex7_27.cpp
Merge pull request #50 from shbling/patch-3

Update ex7_31.cpp
Merge pull request #1 from Mooophy/master

SYN
fix exercise 16.3 16.4

Add a test for exercise 16.3.
A better solution for exercise 16.4.
Merge pull request #52 from Queequeg92/master

add test code for exercise 16.3; improved 16.4.
fix bug
fix bug
Merge pull request #54 from Queequeg92/master

fix a constructor bug
A solution for exercise 16.15
Merge pull request #55 from Queequeg92/master

A solution for exercise 16.15