c ++简单if语句不检查？

Question

i have a 'mouse reader' class which can turn rotations into x,y,z. (It's a kind of first person camera) But i don't want the person to look directly at his axis, so i did this:

if (!(Altitude  +  MouseCoordChange[1] > 269) && !(Altitude  +  MouseCoordChange[1] < 91))
{

I couted the checking and it's perfect, it prevents you from going too much up and down, but some times, it goes under 91 and 269, how is this possible?

Thank You

Answer 1

You've fallen foul of De Morgen's Law

in other words:

!A && !B = !(A || B)

I suspect what you wanted was:

if (!((Altitude  +  MouseCoordChange[1] > 269) || 
      (Altitude  +  MouseCoordChange[1] < 91)))
{

Or even clearer:

if ((Altitude  +  MouseCoordChange[1] <= 269) && 
    (Altitude  +  MouseCoordChange[1] >= 91)))
{

Answer 2

Ok, just for debugging, Try this inverse logic.

if (  (Altitude  +  MouseCoordChange[1] < 91) &&  (Altitude  +  MouseCoordChange[1] > 269)  )
{

  //Do nothing here
}
else
{

  //Do stuff here

}

Answer 3

Range-checking happens quite often so a template will be useful for that:

template< typename _T > bool inrange(_T first, _T last, _T value)
{
    return ((value>=first) && (value<=last));
}

In your case:

if (inrange(91, 269, (Altitude  +  MouseCoordChange[1]))
{
    //is in the range - do something
}
else
{
    //is outside the range - do something
}