private ["_i"];
for [{_i=0},{_i<100},{_i=_i+1}] do {
ctrlSetText [100,format["%1",_i]];
_i = _i - 1;
sleep 1;
};
The string in "For" {_i=_i+1} increases your zero by 1 while "_i=_i -1;" reduces by 1.
So 0 + 1 - 1 = 0.
Change the above to:
private ["_i"];
for [{_i=0},{_i<100},{_i=_i-1}] do {
ctrlSetText [100,format["%1",_i]];
sleep 1;
};
and it will start at 0 and go down by 1 each second.
if you want it to start at 100 and go down replace the {_i=0} with {_i=100};
Hope that helps.
Luke