time.h library

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

#define N 1000000000

clock_t start,stop;

main()
{
    int i;
    double x;

    start = clock();

    for (i=0;i<N;i++)
        x=x*3;

    stop = clock();

    printf("%d %f \n",N,(double) (stop-start)/(CLOCKS_PER_SEC));
}