Finding number of data points in a single grid?

I have a data set of consisting of latitude and longitude coordinates. After plotting my grid and the coordinate points, I want to determine the number of points within a single grid. This is my code so far. However, it can only create the grid and plot the points. It's unable to determine the number of points in a grid. Any idea why my code isn't doing what I want? Thanks in advance.

 %%create grid 
N = 31; % creates a 30x30 grid 
xgrid = linspace(103.6,104,N);
ygrid = linspace(1.25,1.5,N);
[X,Y] = meshgrid(xgrid,ygrid);
figure 
hold on
plot(X,Y,'r');
plot(X',Y','r');
xlim([103.6 104])
ylim([1.25 1.5])

 %%plot coordinate points
plot(coordinates(:,2),coordinates(:,3),'.');

 %%find number of bus stops in a single grid 

 lat = coordinates(:,2); % x coordinates
 lon = coordinates(:,3); % y coordinates

 % create nested for loop 
for i = linspace(103.6,104,(1/75))
    for j = linspace(1.25,1.5,(1/120))

        % index = row number
        index = find(lat > i & lat < i + 1 & lon > j & lon < j + 1); 
        % stn = data point
        stn = coordinates(index,1);

    end
end

Answer 1

[Musa]

Atiqah,

coordinates isn't defined.

[Atiqah Zakirah]

Hey Musa,

My coordinates were from an excel file. I imported the data into Matlab as a numeric matrix called "coordinates" so there isn't a line of code that defines what the coordinates are since there's too many. Must I define it in another way?