benchmarking code

[itcplpl]

hi,
I am trying to write a benchmark program that takes about 20 minutes to complete because the actual functions needs to be called plenty(unknown variable) times.

I have the following code

struct timeval start, end;
  long mtime, seconds, useconds;
gettimeofday(&start, NULL);
 usleep(2000);
gettimeofday(&end,NULL);
 seconds =end.tv_sec - start.tv_sec;
 useconds=end.tv_usec - start.tv_usec;
 mtime=((seconds)*1000 + useconds/1000)+0.5;
 cout<<"elapsed time is:"<<mtime<<" milliseconds\n";

but I am required to write it in such a way that the output deduces the best units to use for the elapsed time and displays the results in those units.
do I need to write an if-else for that?

[kbw]

Yes. You need to determine the range of the number you want to display and use the appropriate format.

[itcplpl]

does that mean something like this

  (mtime>1000)?cout<<"elapsed time in seconds:"<<setprecision(8)<<mtime/1000<<" seconds\n":cout<<"elapsed time in milliseconds: "<<setprecision(3)<<mtime<<" milliseconds\n"; 

also, can you please tell me if mtime should be a long or int or double?