(Probably elementary) Plotting problem

I have some problem with plotting.

Basically I have a vector

a=1:0.2:10

for n=1:1:length(a)
while ... %a bunch of calculations using a(n)
b(n)=b(n)+1
end
end

I want to plot b against a, so I wrote

plot(a,b)

but it doesn't plot the results I got by entering values individually-- when I didn't have the outer for loop . Could somebody please help?

Thank you.

[per isakson]

Looks ok to me. Any error message? Preallocate b = nan(size(a)). The size of a and b?

[Richard]

@per isakson: There isn't an error message. It plots something, but not the right thing...

[per isakson]

@Richard: Put the code in a function and debug your code. Set a break point on the first line and step line by line. Check the values. The problem is hardly with the plot command. Try plot(a,b,'.').