Language C : What Does Comparision of three Numbers retuen.

Well, it doesn't always return 0.

Sometimes it will return 1;  for example if a =2, b = 1, c = 0.

It's executed as if it were written:

x = (a > b) > c;

The bracketed expression returns 1 (for true) if a > b or 0 (for false) if a <= b.

This result is then compared with c using the same principles.

So for the above values of a, b and c, we have:

2 > 1  => true => returns 1
1 > 0  => true => returns 1

If we'd had a = 0, b = 1, c = 2, the result would have been 0 as follows:

0 > 1 => false => returns 0
0 > 2 => false => returns 0