用C写的计算运行时间

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main( void )
{
   long     i = 10000000L;
   clock_t start, finish;
   double   duration;
   printf( "Time to do %ld empty loops is ", i ); 

   start = clock();
   while( i-- )       ;
   finish = clock(); 

   duration = (double)(finish - start) / CLOCKS_PER_SEC;
   printf( "%f seconds", duration );
   system("pause");
}