用c++实现获取程序运行的时间

看代码:
 1 #include<iostream>
 2 #include<ctime>
 3 using namespace std;
 4 int main()
 5 {
 6     int i;
 7     time_t begin,end;
 8     begin=clock();
 9     cout<<"**************************





I love you!




**************************"<<endl;
10     i = 0;
11     while(i++ < 1000000000) ;
12     end=clock();
13     cout<<"runtime:"<<double(end-begin)/CLOCKS_PER_SEC<<"s"<<endl;
14 
15     begin = time(NULL);
16     cout<<"**************************





I love you!




**************************"<<endl;
17     i = 0;
18     while(i++ < 1000000000) ;
19     end = time(NULL);
20     cout << difftime(end, begin) << 's' << endl;
21 }