计算程序运行时间

#include <iostream>  
#include <time.h>
int main(void)   
{  
    int sum = 0;
    time_t t,t1;        time(&t);        //t = time(NULL);
    std::cout<<ctime(&t);        //单位为秒

    int star = clock();                //单位毫秒
    for (int i=1; i <=10000; ++i) 
    {  
        sum = sum+i;
    }  
    std::cout<<sum<<std::endl;
    int stop = clock();
    std::cout<<stop - star<<"毫秒"<<std::endl;
    time(&t1);        
    int t3 = t1-t;
    std::cout<<t3<<" 秒"<<std::endl;
    std::cout<<ctime(&t1);        
    system("pause");
    return 0;  
}