for loop i=0:0.5:pi;
This is no valid Matlab syntax. You can run code directly in the forum's interface and you will get an error message for this. A valid loop would be:
for i=0:0.5:pi
This creates i=0, i=0.5, ... iteratively. Of course all i are scalars - this is the purpose of a loop counter.
Your pseudo-code contains the solution of your problem already: Simply omit the for loop, but define the output directly:
i=0:0.5:pi;
Now you can access w.g. i(2) and i(3).
I suggest the free Matlab tutorial to learn such basics: https://www.mathworks.com/learn/tutorials/matlab-onramp.html
