'for loop' for beginners?

I'm having trouble figuring out a for loop command. I'm trying to make a matlab script that allows the user to input a row vector, and then it outputs a new vector of 0's and 1's. 0's for negative numbers and 1's for non negative numbers.

so far what i have is:

v=input('Enter elements of vector: \n');
 % after entering v,run below code
 for i = 1:length(v)
     if v(i) > 0
        sprintf('v(%i)>0',i)
     elseif v(i) <0
        sprintf('v(%i)<0',i)
     end
 end

but when I finish, i get "Error: Unexpected MATLAB expression." So I guess I just need to know where I'm going wrong and what I need to do differently. I'm not sure how to make the loop output it when it's done either. Thanks in advance for your help!

edit: I also tried:

v=input('Enter elements of vector: \n');
 % after entering v,run below code
 for i = 1:length(v)
     if v(i) > 0
        v(i)=1
     elseif v(i) <0
        v(i)=0
     else
        v(i)=0
     end
 end

which also doesn't work. I'm not sure how to get the program to replace the values from the old vector with 0's and 1's based on whether or not they are positive. Thanks again.

Answer 1

[Image Analyst]

Here's one way that works.

str = input('Enter elements of vector: \n', 's');
v = cell2mat(textscan(str, '%f,'))
% After entering v,run below code
for i = 1:length(v)
     if v(i) > 0
        v(i)=1
     elseif v(i) <= 0
        v(i)=0
     end
end

Of course the for loop could be replaced by a vectorized solution

v = v>0;

[Andrew Ardolino]

This is helpful, but just displays the numbers that are non-zero. Is there a way to make it from like

v=[1 0 -3 6 2 -7]
to 
v= [1 1 0 1 1 0]

1's being true for non-zero numbers?

[Image Analyst]

It does do that if you put commas between the numbers and omit the brackets.

[Andrew Ardolino]

Errr what do you mean? Sorry I'm incompetent and super new to matlab.

[Image Analyst]

At the prompt when it's waiting for your input, type

1, 0, -3, 6, 2, -7

instead of

[1 0 -3 6 2 -7]

[Andrew Ardolino]

oh wow, jeez thank you so much.

Answer 2

[Iain]

The error is because you're trying to get the user to enter a list of numbers with a function that only allows ONE number to be input.

If you replace:

 v=input('Enter elements of vector: \n');

with

 v = [4 5 3 6 1 -34 -56];

How you get the list of numbers from the user is up to you - you can either put it in a loop (while loop), or you can change your code to accept an input, then have the user call it, like sin([0 pi/2 pi])

You'll see that it works.