how to graph using loop?

I want to calculate a problem and graph it

I want to graph i and area but it only show one point on my graph

% question1
clear all
a = 1
vectori = []    
areavec = []
figure;
for i = 0:20
    a = a + a
    area = a *(1/8).^i
    scatter(i,area)
end

Answer 1

[the cyclist]

Put the command

hold on

on the line after figure.

See the documentation for the hold command for details.

Answer 2

[Setsuna Yuuki.]

You must change this:

clear all
a = 1
vectori = []% ??
areavec = []
figure;
for i = 0:20
    a = a + a
    areavec(i+1) = a *(1/8).^i %area --> areavec and areavec is a vector, not a scalar
end
i = 0:20;
scatter(i,areavec) %area --> areavec and graph must be out of cycle

[Khang Nguyen]

this is what the out put says for me "Array indices must be positive integers or logical values." on line 9

[the cyclist]

vectori is not used in the rest of the code. I commented it out completely, and the code runs.

[Setsuna Yuuki.]

I edited my answer, now this works :D

[Khang Nguyen]

lovely: thanks