Different increment on a for loop depending on a boolean

Different increment on a for loop depending on a boolean

How can i select the increment on a for loop depending on a boolean,i am
trying to do something like this:
for (int y = iniY; isdown? (y >= endY): (y <= iniY+dy) ; isdown?
--y:y++);
the for loop accepts the termination but not the increment...
The working code i currently have is something like this:
if(isdown)
for (int y = iniY; y >= endY; --y) {
code lines...
}
else
for (int y = iniY; y <= iniY+dy; ++y) {
code lines...
}
the code can not be extracted to a new method because it works on many
variables...