Update ex5_24.cpp

增加头文件以使得编译通过。
Merge pull request #5 from wgqimut/patch-2

Update ex5_24.cpp
fix a bug
Revert "fix a bug"

This reverts commit c1f744dc47b149235ca97565d8aa523f14a2ec00.
fix a bug
fix the layout
fixed #6
Merge branch 'evan617-master'

improve the answer of exercise 3.37
fixed bugs of ex6_27 and ex6_28
fix some bugs
Fix the exercise4.30
Merge branch 'master' of https://github.com/evan617/Cpp-Primer into evan617-master
Merge branch 'evan617-master'
better answer of ex4_30
fixed confilcts
Merge pull request #37 from pezy/master

fixed some bugs.