Bishop Move

we need to calculate the allowed move for Bishop by the given position

we start with a Bishop on c6, what positions can it reach in one move? => output should include b5, a4, b7, a8

// this function draw the chess positions
static IEnumerable<string> GetBoardPositions()
{
//draw rows 
    return Enumerable.Range('a', 8).
//draw columns 
    SelectMany(
        x => Enumerable.Range('1', 8), (f, r) => 
// string format for showing position
            String.Format("{0}{1}",(char)f, (char)r));
}

the 64 positions list

// calculate the allowed move by given (startPosition=> that can move)
// and targetPostion => that current position of Bishop
static bool BishopCanMoveTo(string startPos, string targetPos)
{

    var dx = Math.Abs(startPos[0] - targetPos[0]);
    var dy = Math.Abs(startPos[1] - targetPos[1]);
    return dx == dy && dx != 0;
}

// the result
GetBoardPositions().Where(p => BishopCanMoveTo(p,"c6"))

the allowed position that Bishop can move