Worst run-time for 3 nested loop
I suggest you slightly modify your program, as follows:

int i, j, k, t = 0;
for (i = 0; i &lt;= n - 1; i++)
  for (j = i + 1; j &lt;= n - 1; j++)
    for (k = j + 1; k &lt;= n - 1; k++)
      t++;


Now run this program for various values of $n$ and print the corresponding values of $t$, which is your runtime $T(n)$. Make a guess at the growth rate of $T(n)$ based on this. Try to prove your guess.

Another idea is to try to understand what happens when you have only one loop, then two nested loops, and then all three nested loops. The first case in particular is pretty easy.