Operating System question

/* Program to demonstrate time taken by function fun() */ #include <stdio.h> #include <time.h> // A function that terminates when enter key is pressed void fun() { printf("fun() starts \n"); printf("Press enter to stop fun \n"); while(1) { if (getchar()) break; } printf("fun() ends \n"); } // The main program calls fun() and measures time taken by fun() int main() { // Calculate the time taken by fun() struct timespec start, finish; double elapsed; clock_t t; t = clock(); clock_gettime(CLOCK_MONOTONIC, &start); printf("start %ld\n", start.tv_sec); fun(); clock_gettime(CLOCK_MONOTONIC, &finish); printf("finish %ld\n", finish.tv_sec); //printf("CLOCKSPERSEC %ld\n", CLOCKS_PER_SEC); //double time_taken = ((double)t)*1000.0/CLOCKS_PER_SEC; // in seconds elapsed = (finish.tv_sec - start.tv_sec); //Alternative with more precision: //elapsed += (finish.tv_nsec - start.tv_nsec) / 1000000000.0; printf("fun() took %f seconds to execute \n", elapsed); return 0; }