How to find the points in specific areas of the graph

When i plug this into matlab i am trying to get the amount of dots per area in the graph produced. (ar1...ar4). I tried to find the area above and below sections of the lines that run through the graph but I keep messing it up. What can I change to correct this issue?

n = 
for k = 1:20
x = 8 * rand(1,n);
y = 8 * rand(1,n); 
hold off
scatter (x,y)

hold on 
u = [0:0.01:8];
for i = 1: length(u)
    v1(i) = u(i);
    if u(i) <= 8
        v2(i) = 8-u(i); 
        u(i) - u(i);
    end
end
plot(u,v1,u,v2)
 ar1 = 0;
 ar2 = 0; 
 ar3 = 0;
 ar4 = 0;
for  i = 1:length(x)
    if y(i) > x(i) 
        ar1 = ar1 +1;
    else
        if y(i)< 8-x(i)
        ar2 = ar2 +1;
        else
            ar3= ar3+1;
        end
    end
    
end
    end

Answer 1

[KSSV]

YOu have the lines/ boundaries of your required area in hand. Use inpolygon to get the points/ dots that lie inside the give area. Read about inpolygon.