Iterate through an array

Using Arduino Programming Questions
1

Good evening all, please somebody help me with this issue.

I have an array as shown in the code below. I am interested in the third (X), and fourth (Y) column. I would like to write a loop to subtract the current value from the next value. Something like this: d = x(i+1) - xi; a = y(i+1) - yi;

struct LatLon
{
  double Lat;
  double Lon;
  double X;
  double Y;
};

static const LatLon LatLonList[] =
{
{6.86899, 7.41179, 0, 0},
{6.86898102641852, 7.41178940176106, 1.5, 2},
{6.86897205283705, 7.41178880352213, 2.5, 3},
{6.86896307925557, 7.41178820528321, 4, 5},
{6.86895410567409, 7.4117876070443, 6, 7},
{6.86894513209261, 7.4117870088054, 8, 9},
{6.86893615851114, 7.41178641056651, 10, 11},
{6.86892718492966, 7.41178581232764, 12, 13},
{6.86891821134818, 7.41178521408877, 20, 21},
{6.86890923776671, 7.41178461584992, 32, 34},
};
2 
1: 1.50 2.00
2: 1.00 1.00
3: 1.50 2.00
4: 2.00 2.00
5: 2.00 2.00
6: 2.00 2.00
7: 2.00 2.00
8: 8.00 8.00
9: 12.00 13.00

struct LatLon
{
    double Lat;
    double Lon;
    double X;
    double Y;
};


static const LatLon lats [] =
{
    {6.86899, 7.41179, 0, 0},
    {6.86898102641852, 7.41178940176106, 1.5, 2},
    {6.86897205283705, 7.41178880352213, 2.5, 3},
    {6.86896307925557, 7.41178820528321, 4, 5},
    {6.86895410567409, 7.4117876070443, 6, 7},
    {6.86894513209261, 7.4117870088054, 8, 9},
    {6.86893615851114, 7.41178641056651, 10, 11},
    {6.86892718492966, 7.41178581232764, 12, 13},
    {6.86891821134818, 7.41178521408877, 20, 21},
    {6.86890923776671, 7.41178461584992, 32, 34},
};

const int Nlat = sizeof(lats)/sizeof(LatLon);

void setup ()
{
    Serial.begin (9600);

    for (int i = 1; i < Nlat; i++)  {
        float d = lats [i].X - lats [i-1].X;
        float a = lats [i].Y - lats [i-1].Y;

        Serial.print (i);
        Serial.print (": ");
        Serial.print (d);
        Serial.print (" ");
        Serial.print (a);
        Serial.println ();
    }
}

void loop ()
{
}
3 
double d = LatLonList[i+1].X -  LatLonList[i].X;
double a = LatLonList[i+1].Y -  LatLonList[i].Y;
4

Thank you!

5

Please place solution mark to the post #2 as a more complete answer.