Create a grid and assign values - c++

Question

I would like to create a 2D squared grid of the world with a definite spacing (say d)
-180 =< j =< 180
-90 =< k =< 90
Grid[j][k]
and then assign to each cell the lon lat points that I have stored in two arrays
0 =< i < N
Lon[i]
Lat[i]
to group the observations by cells.
I was thinking of using nested loops to create the grid but I am not really sure how to to that.
Many thanks

Answer 1

You're probably going to be yelled at by the SO community for a novice question without a lot of signs of research. But here's my obligatory answer.
struct Position
{
double Lon, Lat;
}
const unsigned short lonCount = 180;
const unsigned short latCount = 360;
Position positions[lonCount][latCount];
for( unsigned short lon = -90; lon <= 90; lon++ )
{
for( unsigned short lat = -180; lat <= 180; lat++ )
{
Position* p = &positions[lon + lonCount / 2][lat + latCount / 2];
p->Lon = lon;
p->Lat = lat;
}
}
This should get you started.

Answer 2

struct Position {
double Lon, Lat;
int index;
};
int main(){
printf ("\n");
static const double arrlon[] = {100,180,180};
static const double arrlat[] = {0,2,3};
static const int arrind[] = {0,0,0};
vector<double> londat (arrlon, arrlon + sizeof(arrlon) / sizeof(arrlon[0]));
vector<double> latdat (arrlat, arrlat + sizeof(arrlat) / sizeof(arrlat[0]));
vector<int> index (arrind, arrind + sizeof(arrind) / sizeof(arrind[0]));
int N = sizeof(arrlat)/ sizeof(arrlat[0]) ;
const int lonCount = 360;
const int latCount = 180;
const int step = 5;
Position positions[lonCount+1][latCount+1];
Position* p;
int count = 0;
for(int lon = 0; lon <= 360; lon=lon+step){
for(int lat = 0; lat <= 180; lat=lat+step){
p = &positions[lon][lat];
p->Lon = lon;
p->Lat = lat;
p->index = count;
count++;
for (int i = 0; i<N ; i++){
if(londat[i] >= p->Lon && londat[i] < p->Lon+step && latdat[i] >= p->Lat && latdat[i] < p->Lat+step) index[i] = p->index;
}
}
}
for (int i = 0; i<N ; i++) cerr << i << " " << index[i] << endl;
return 0;
}