CPU Timing in a C code

Examine this simple example :

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

int main();

int main() {
  long int i,a;
  clock_t cputime,cputime1;
  double timing,timing0;
   cputime= clock();
    for(i=0;i<10000000;i++){
       a=pow(4,2);
       a=pow(4,2);
       a=pow(4,2);
       a=pow(4,2);
       a=pow(4,2);
      }

   cputime1= clock();
   timing0=((double) cputime1-cputime);
   timing=((double) cputime1-cputime) / CLOCKS_PER_SEC;
   printf("timing =%12.9f clock per sec=%d timing0=%12.9f\n",
          timing,CLOCKS_PER_SEC,timing0);
   exit(0);
}