Calculate execution time in C

exec_time.c

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

/* https://www.educative.io/edpresso/what-is-clockt-in-c */
int main() {
  clock_t start_ticks = clock();

  size_t n_iters = pow(10, 9);
  for (size_t i = 0; i < n_iters; i++) {
    log(10);
  }

  clock_t end_ticks = clock();
  clock_t elapsed_ticks = end_ticks - start_ticks;

  float duration = (float) elapsed_ticks / CLOCKS_PER_SEC;
  printf("Exec. time: %f s\n", duration);

  return 0;
}