求程序耗时的一种方法

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

int main( void )
... {
time_tstart,finish;
longloop;
doubleresult,elapsed_time;

printf("Multiplying2floatingpointnumbers500milliontimes... ");

time(&start);
for(loop=0;loop<500000000;loop++)
result=3.63*5.27;
time(&finish);

elapsed_time=difftime(finish,start);//得到秒数
printf(" Programtakes%6.0fseconds. ",elapsed_time);
}