c语言time与clock区别

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

int main()
{
long i=0;
float j=0;
clock_t start_clock=clock();
time_t start_time=time(NULL);
for(i=0;i<100000000;i++)
{
j=(float)i*213124/200000;

}
//sleep(3);
printf("processor time used is:%g sec. ,j= %d \n",(clock()-start_clock)/(double) CLOCKS_PER_SEC,j);
printf("Running time :%g sec. \n",difftime(time(NULL),start_time));
return 0;
}

processor time used is:0.71 sec. ,j= 1073741824
Running time :1 sec.