for (i = 10; i >=0; i–) ---- is faster than ----- for(i = 0; i <10; i++) --- WHY?

Answer 1

There is no difference in speed that you could experience, but there actually could be.

C compilers have optimizators that in some cases use CPU assembly commands that are faster to execute.

If you select that speed is to be optimized (not size), the
for (i = 10; i >=0; i–)
could be translated in assembly code to something like
i = 10
Loop:
(code)
i--
jump if not zero to Loop

while for(i = 0; i <10; i++) is
i = 0
Loop:
(code)
i++
compare i with 10
jump if less to Loop

You see that there is an additional (compare i<10) assembly command needed and it makes the difference in speed.

Answer 2

actually your wrong because the first one goes through 11 items and the second only goes through ten.. 10 - 0 and then 0 - 9 ( you wrote < 10 not <=).

Answer 3

It shouldn't be... your first statement [ for(i=10;i>=0;i--) ] runs 11 times, while your second statement runs 10 times...

Answer 4

Just did some tests... it isn't.