Instead of naming your variables dynamically, which is almost always a bad idea, store your data in cell arrays. Then the length of the cell array will be the number of calls of the loop:
rng default
% Make up three datasets, stored in cell arrays
C{1} = sort(rand(3,1));
V{1} = rand(3,1);
C{2} = sort(rand(2,1));
V{2} = rand(2,1);
C{3} = sort(rand(5,1));
V{3} = rand(5,1);
% There could be more. Even if you uncomment this to get a new dataset, the
% plotting routine doesn't need to change.
% C{4} = sort(rand(5,1));
% V{4} = rand(5,1);
% Plot, looping over the cell array
figure
hold on
for n = 1:length(C)
plot(C{n},V{n})
end
