Question about switch/case inside loop

gpeddino

In a loop like this, shouldn't the switch/case changes in the iX and iY values happen separately? When I use this, they add up to one another (case 1, then case 1 + case 2, etc). I tried using if/elses but the same thing happened. Is there something here I'm not seeing? I'm trying to create a chess game and this script is supposed to check the availability of spaces around the king.

                int xCount = 1;
                for (xCount = 1; xCount <= 8; xCount++)
                {
                    switch (xCount)
                    {
                        case 1: iY++; break; /// Forward
                        case 2: iX++; break; /// Forward + Right
                        case 3: iY--; break; /// Right
                        case 4: iY--; break; /// Backward + Right
                        case 5: iX--; break; /// Backward
                        case 6: iX--; break; /// Backward + Left
                        case 7: iY++; break; /// Left
                        case 8: iY++; break; /// Forward + Left
                    }

ForSerious

Usually for a chess game you would have a 2D array that defines the board. In the array, you would store the locations of all the pieces. Since your loop is not checking against such an array, nothing happens except some counting.

Melkior

The ++ and -- operators actually add or subtract one from the control variables, so subtracting one later on won't make the variable point to the place which you're probably thinking it would point to, unless you're resetting the iX and iY variables before re-starting each iteration through the loop.

A better way is to have "interim" variables which take the value of iX and iY after either adding or subtracting one, as required. This will leave the iX and iY variables unchanged so that they don't need to be re-set on each pass.

// define iX1 and iY1 earlier in the code as integers
// do the preliminaries including the loop and opening the select case statement

case 1: iX1=iX+1; iY1=iY; break; // Right
case 2: iX1=iX+1; iY1=iY+1; break; // Right and Down
case 3: iX1=iX; iY1=iY+1; break; // Down
case 4: iX1=iX-1; iY1=iY; break; // Left
case 5: iX1=iX-1; iY1=iY+1; break; // Left and Down
case 6: iX1=iX-1; iY1=iY-1; break; // Left and Up
case 7: iX1=iX; iY1=iY-1; break; // Up
case 8: iX1=iX+1; iY1=iY-1; break; // Right and Up

// close the select case statement
// do whatever operations are required

You use iX1 and iY1 instead of iX and iY, so that you don't disturb the values of the original iX and iY variables.

Melkior

Putting it more simply, using "iX++;" has the same result as using "iX=iX+1" except that the ++ version generally compiles into shorter code for reasons related to how the machine code instructions work.
Because you're going through the loop eight times, the instructions on every line get done once, so by the time the loop ends, the value in the variables will wind up being the sum of all of those increments and decrements.
If I manually add and subtract all of those lines, as would happen if the loop ran 8 times, then by the time the loop ends, iX will wind up being one less than it was while iY will wind up being one more than it was. If that's not what you intended, then there's the source of your problem.
In the interim, the values of iX and iY will probably wind up with them pointing to the wrong places.
(Note that when I made the above code, I assumed an array starting at the top, left rather than bottom left. You'll need to reverse the + and - for the values of iY if your code assumes starting at bottom left)