Add a for loop for each file as follows:
for k = 1:numel(N)
baseFileName = N{k};
%for k = 1 : length(theFiles)
% baseFileName = theFiles(k).name;
fullFileName = fullfile(myFolder, baseFileName);
fprintf(1, 'Now reading %s\n', fullFileName);
data{k}=dlmread(fullFileName);
for s = 1:size(data{k},2)/2
x=data{k}(:,2*s-1);
y=data{k}(:,2*s);
xm = mean(x);
ym = mean(y);
x = x - xm;
y = y - ym;
% summations for CCW boundary
xp = x( [2:end 1] );
yp = y( [2:end 1] );
a = x.*yp - xp.*y;
l=t*k;
A{k,s} = sum( a ) /2;
xc{k,s} = sum( (x+xp).*a ) /6/A{k,s};
yc{k,s} = sum( (y+yp).*a ) /6/A{k,s};
% replace mean of vertices
x_cen{k,s} = xc{k,s} + xm;
y_cen{k,s} = yc{k,s} + ym;
fprintf(fileID,'\n%f %d %f %f\n',l,s, x_cen{k,s}, y_cen{k,s});
end
end
fclose(fileID);
return
