plotting trouble

can anyone help me see what im doing wrong here i want to plot this with a for loop

for i=1:20
    x= i
    y=x
end
plot(x,y)

but when i plot it,there is no graph in the figure window and the graph has a really weird range that i didnt input however when i try this it works just fine why is that

x=1:1:20
    y=x
plot(x,y)

Answer 1

[Fangjun Jiang]

In your for-loop, x and y are assigned a value one at a time. x and y are always over-written. So at the end of the loop, you end up with x==20 and y==20. The plot just shows one dot.

In the second approach, x is a vector and so is y.