Hi, I want to compare time of execution a recursive and nonrecursive program!

I tried using function clock() but it seems that my program is so fast that I always get result 0.00000.

I did search a board but didn't find the answer how to measure very fast executions.

I wonder if this is a correct way to solve this:

I want to display time in microseconds!Code:#include <stdio.h> #include <time.h> #define MAX 1000000 long fact(int); long fact_rec(int); int main ( void ) { long res; int i; double duration; clock_t start,end; start=clock(); for(i=0;i<MAX;i++) res=fact(10); end=clock(); duration=(double)(end-start)/(double)(CLOCKS_PER_SEC); printf("Duration is %lf us!",duration); return 0; } long fact(int n) { int i; long res=1; if(n<=0) return 1; for(i=2;i<=n;i++) res*=i; return res; } long fact_rec(int n) { if(n<=0) return 1; return n*fact_rec(n-1); }

I figure that if (double)(end-start)/(double)(CLOCKS_PER_SEC) is time in seconds, all I need to do is to multiply with 1000000, and because of loop I need to divide with 1000000 to get average time. I get these results:

fact(10) => duration 0.45 us

fact_rec(10) => duration 1.842 us.

Is this a correct way of measuring time?

Interesting If I execute recursive function fact_rect and start program I wait 2-3 seconds program to finish and then I get results displayed 1.842 us that is 1.8 million part of sec (us) and I wait program to finish at least 3 seconds.

Why is that happening?

Thanks!